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cpython/Python/perf_jit_trampoline.c

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/*
* Python Perf Trampoline Support - JIT Dump Implementation
*
* This file implements the perf jitdump API for Python's performance profiling
* integration. It allows perf (Linux performance analysis tool) to understand
* and profile dynamically generated Python bytecode by creating JIT dump files
* that perf can inject into its analysis.
*
*
* IMPORTANT: This file exports specific callback functions that are part of
* Python's internal API. Do not modify the function signatures or behavior
* of exported functions without coordinating with the Python core team.
*
* Usually the binary and libraries are mapped in separate region like below:
*
* address ->
* --+---------------------+--//--+---------------------+--
* | .text | .data | ... | | .text | .data | ... |
* --+---------------------+--//--+---------------------+--
* myprog libc.so
*
* So it'd be easy and straight-forward to find a mapped binary or library from an
* address.
*
* But for JIT code, the code arena only cares about the code section. But the
* resulting DSOs (which is generated by perf inject -j) contain ELF headers and
* unwind info too. Then it'd generate following address space with synthesized
* MMAP events. Let's say it has a sample between address B and C.
*
* sample
* |
* address -> A B v C
* ---------------------------------------------------------------------------------------------------
* /tmp/jitted-PID-0.so | (headers) | .text | unwind info |
* /tmp/jitted-PID-1.so | (headers) | .text | unwind info |
* /tmp/jitted-PID-2.so | (headers) | .text | unwind info |
* ...
* ---------------------------------------------------------------------------------------------------
*
* If it only maps the .text section, it'd find the jitted-PID-1.so but cannot see
* the unwind info. If it maps both .text section and unwind sections, the sample
* could be mapped to either jitted-PID-0.so or jitted-PID-1.so and it's confusing
* which one is right. So to make perf happy we have non-overlapping ranges for each
* DSO:
*
* address ->
* -------------------------------------------------------------------------------------------------------
* /tmp/jitted-PID-0.so | (headers) | .text | unwind info |
* /tmp/jitted-PID-1.so | (headers) | .text | unwind info |
* /tmp/jitted-PID-2.so | (headers) | .text | unwind info |
* ...
* -------------------------------------------------------------------------------------------------------
*
* As the trampolines are constant, we add a constant padding but in general the padding needs to have the
* size of the unwind info rounded to 16 bytes. In general, for our trampolines this is 0x50
*/
#include "Python.h"
#include "pycore_ceval.h" // _PyPerf_Callbacks
#include "pycore_frame.h"
#include "pycore_interp.h"
#include "pycore_runtime.h" // _PyRuntime
#ifdef PY_HAVE_PERF_TRAMPOLINE
/* Standard library includes for perf jitdump implementation */
#include <elf.h> // ELF architecture constants
#include <fcntl.h> // File control operations
#include <stdio.h> // Standard I/O operations
#include <stdlib.h> // Standard library functions
#include <sys/mman.h> // Memory mapping functions (mmap)
#include <sys/types.h> // System data types
#include <unistd.h> // System calls (sysconf, getpid)
#include <sys/time.h> // Time functions (gettimeofday)
#include <sys/syscall.h> // System call interface
// =============================================================================
// CONSTANTS AND CONFIGURATION
// =============================================================================
/*
* Memory layout considerations for perf jitdump:
*
* Perf expects non-overlapping memory regions for each JIT-compiled function.
* When perf processes the jitdump file, it creates synthetic DSO (Dynamic
* Shared Object) files that contain:
* - ELF headers
* - .text section (actual machine code)
* - Unwind information (for stack traces)
*
* To ensure proper address space layout, we add padding between code regions.
* This prevents address conflicts when perf maps the synthesized DSOs.
*
* Memory layout example:
* /tmp/jitted-PID-0.so: [headers][.text][unwind_info][padding]
* /tmp/jitted-PID-1.so: [headers][.text][unwind_info][padding]
*
* The padding size (0x100) is chosen to accommodate typical unwind info sizes
* while maintaining 16-byte alignment requirements.
*/
#define PERF_JIT_CODE_PADDING 0x100
/* Convenient access to the global trampoline API state */
#define trampoline_api _PyRuntime.ceval.perf.trampoline_api
/* Type aliases for clarity and portability */
typedef uint64_t uword; // Word-sized unsigned integer
typedef const char* CodeComments; // Code comment strings
/* Memory size constants */
#define MB (1024 * 1024) // 1 Megabyte for buffer sizing
// =============================================================================
// ARCHITECTURE-SPECIFIC DEFINITIONS
// =============================================================================
/*
* Returns the ELF machine architecture constant for the current platform.
* This is required for the jitdump header to correctly identify the target
* architecture for perf processing.
*
*/
static uint64_t GetElfMachineArchitecture(void) {
#if defined(__x86_64__) || defined(_M_X64)
return EM_X86_64;
#elif defined(__i386__) || defined(_M_IX86)
return EM_386;
#elif defined(__aarch64__)
return EM_AARCH64;
#elif defined(__arm__) || defined(_M_ARM)
return EM_ARM;
#elif defined(__riscv)
return EM_RISCV;
#else
Py_UNREACHABLE(); // Unsupported architecture - should never reach here
return 0;
#endif
}
// =============================================================================
// PERF JITDUMP DATA STRUCTURES
// =============================================================================
/*
* Perf jitdump file format structures
*
* These structures define the binary format that perf expects for JIT dump files.
* The format is documented in the Linux perf tools source code and must match
* exactly for proper perf integration.
*/
/*
* Jitdump file header - written once at the beginning of each jitdump file
* Contains metadata about the process and jitdump format version
*/
typedef struct {
uint32_t magic; // Magic number (0x4A695444 = "JiTD")
uint32_t version; // Jitdump format version (currently 1)
uint32_t size; // Size of this header structure
uint32_t elf_mach_target; // Target architecture (from GetElfMachineArchitecture)
uint32_t reserved; // Reserved field (must be 0)
uint32_t process_id; // Process ID of the JIT compiler
uint64_t time_stamp; // Timestamp when jitdump was created
uint64_t flags; // Feature flags (currently unused)
} Header;
/*
* Perf event types supported by the jitdump format
* Each event type has a corresponding structure format
*/
enum PerfEvent {
PerfLoad = 0, // Code load event (new JIT function)
PerfMove = 1, // Code move event (function relocated)
PerfDebugInfo = 2, // Debug information event
PerfClose = 3, // JIT session close event
PerfUnwindingInfo = 4 // Stack unwinding information event
};
/*
* Base event structure - common header for all perf events
* Every event in the jitdump file starts with this structure
*/
struct BaseEvent {
uint32_t event; // Event type (from PerfEvent enum)
uint32_t size; // Total size of this event including payload
uint64_t time_stamp; // Timestamp when event occurred
};
/*
* Code load event - indicates a new JIT-compiled function is available
* This is the most important event type for Python profiling
*/
typedef struct {
struct BaseEvent base; // Common event header
uint32_t process_id; // Process ID where code was generated
uint32_t thread_id; // Thread ID where code was generated
uint64_t vma; // Virtual memory address where code is loaded
uint64_t code_address; // Address of the actual machine code
uint64_t code_size; // Size of the machine code in bytes
uint64_t code_id; // Unique identifier for this code region
/* Followed by:
* - null-terminated function name string
* - raw machine code bytes
*/
} CodeLoadEvent;
/*
* Code unwinding information event - provides DWARF data for stack traces
* Essential for proper stack unwinding during profiling
*/
typedef struct {
struct BaseEvent base; // Common event header
uint64_t unwind_data_size; // Size of the unwinding data
uint64_t eh_frame_hdr_size; // Size of the EH frame header
uint64_t mapped_size; // Total mapped size (with padding)
/* Followed by:
* - EH frame header
* - DWARF unwinding information
* - Padding to alignment boundary
*/
} CodeUnwindingInfoEvent;
// =============================================================================
// GLOBAL STATE MANAGEMENT
// =============================================================================
/*
* Global state for the perf jitdump implementation
*
* This structure maintains all the state needed for generating jitdump files.
* It's designed as a singleton since there's typically only one jitdump file
* per Python process.
*/
typedef struct {
FILE* perf_map; // File handle for the jitdump file
PyThread_type_lock map_lock; // Thread synchronization lock
void* mapped_buffer; // Memory-mapped region (signals perf we're active)
size_t mapped_size; // Size of the mapped region
int code_id; // Counter for unique code region identifiers
} PerfMapJitState;
/* Global singleton instance */
static PerfMapJitState perf_jit_map_state;
// =============================================================================
// TIME UTILITIES
// =============================================================================
/* Time conversion constant */
static const intptr_t nanoseconds_per_second = 1000000000;
/*
* Get current monotonic time in nanoseconds
*
* Monotonic time is preferred for event timestamps because it's not affected
* by system clock adjustments. This ensures consistent timing relationships
* between events even if the system clock is changed.
*
* Returns: Current monotonic time in nanoseconds since an arbitrary epoch
*/
static int64_t get_current_monotonic_ticks(void) {
struct timespec ts;
if (clock_gettime(CLOCK_MONOTONIC, &ts) != 0) {
Py_UNREACHABLE(); // Should never fail on supported systems
return 0;
}
/* Convert to nanoseconds for maximum precision */
int64_t result = ts.tv_sec;
result *= nanoseconds_per_second;
result += ts.tv_nsec;
return result;
}
/*
* Get current wall clock time in microseconds
*
* Used for the jitdump file header timestamp. Unlike monotonic time,
* this represents actual wall clock time that can be correlated with
* other system events.
*
* Returns: Current time in microseconds since Unix epoch
*/
static int64_t get_current_time_microseconds(void) {
struct timeval tv;
if (gettimeofday(&tv, NULL) < 0) {
Py_UNREACHABLE(); // Should never fail on supported systems
return 0;
}
return ((int64_t)(tv.tv_sec) * 1000000) + tv.tv_usec;
}
// =============================================================================
// UTILITY FUNCTIONS
// =============================================================================
/*
* Round up a value to the next multiple of a given number
*
* This is essential for maintaining proper alignment requirements in the
* jitdump format. Many structures need to be aligned to specific boundaries
* (typically 8 or 16 bytes) for efficient processing by perf.
*
* Args:
* value: The value to round up
* multiple: The multiple to round up to
*
* Returns: The smallest value >= input that is a multiple of 'multiple'
*/
static size_t round_up(int64_t value, int64_t multiple) {
if (multiple == 0) {
return value; // Avoid division by zero
}
int64_t remainder = value % multiple;
if (remainder == 0) {
return value; // Already aligned
}
/* Calculate how much to add to reach the next multiple */
int64_t difference = multiple - remainder;
int64_t rounded_up_value = value + difference;
return rounded_up_value;
}
// =============================================================================
// FILE I/O UTILITIES
// =============================================================================
/*
* Write data to the jitdump file with error handling
*
* This function ensures that all data is written to the file, handling
* partial writes that can occur with large buffers or when the system
* is under load.
*
* Args:
* buffer: Pointer to data to write
* size: Number of bytes to write
*/
static void perf_map_jit_write_fully(const void* buffer, size_t size) {
FILE* out_file = perf_jit_map_state.perf_map;
const char* ptr = (const char*)(buffer);
while (size > 0) {
const size_t written = fwrite(ptr, 1, size, out_file);
if (written == 0) {
Py_UNREACHABLE(); // Write failure - should be very rare
break;
}
size -= written;
ptr += written;
}
}
/*
* Write the jitdump file header
*
* The header must be written exactly once at the beginning of each jitdump
* file. It provides metadata that perf uses to parse the rest of the file.
*
* Args:
* pid: Process ID to include in the header
* out_file: File handle to write to (currently unused, uses global state)
*/
static void perf_map_jit_write_header(int pid, FILE* out_file) {
Header header;
/* Initialize header with required values */
header.magic = 0x4A695444; // "JiTD" magic number
header.version = 1; // Current jitdump version
header.size = sizeof(Header); // Header size for validation
header.elf_mach_target = GetElfMachineArchitecture(); // Target architecture
header.process_id = pid; // Process identifier
header.time_stamp = get_current_time_microseconds(); // Creation time
header.flags = 0; // No special flags currently used
perf_map_jit_write_fully(&header, sizeof(header));
}
// =============================================================================
// DWARF CONSTANTS AND UTILITIES
// =============================================================================
/*
* DWARF (Debug With Arbitrary Record Formats) constants
*
* DWARF is a debugging data format used to provide stack unwinding information.
* These constants define the various encoding types and opcodes used in
* DWARF Call Frame Information (CFI) records.
*/
/* DWARF Call Frame Information version */
#define DWRF_CIE_VERSION 1
/* DWARF CFA (Call Frame Address) opcodes */
enum {
DWRF_CFA_nop = 0x0, // No operation
DWRF_CFA_offset_extended = 0x5, // Extended offset instruction
DWRF_CFA_def_cfa = 0xc, // Define CFA rule
DWRF_CFA_def_cfa_offset = 0xe, // Define CFA offset
DWRF_CFA_offset_extended_sf = 0x11, // Extended signed offset
DWRF_CFA_advance_loc = 0x40, // Advance location counter
DWRF_CFA_offset = 0x80 // Simple offset instruction
};
/* DWARF Exception Handling pointer encodings */
enum {
DWRF_EH_PE_absptr = 0x00, // Absolute pointer
DWRF_EH_PE_omit = 0xff, // Omitted value
/* Data type encodings */
DWRF_EH_PE_uleb128 = 0x01, // Unsigned LEB128
DWRF_EH_PE_udata2 = 0x02, // Unsigned 2-byte
DWRF_EH_PE_udata4 = 0x03, // Unsigned 4-byte
DWRF_EH_PE_udata8 = 0x04, // Unsigned 8-byte
DWRF_EH_PE_sleb128 = 0x09, // Signed LEB128
DWRF_EH_PE_sdata2 = 0x0a, // Signed 2-byte
DWRF_EH_PE_sdata4 = 0x0b, // Signed 4-byte
DWRF_EH_PE_sdata8 = 0x0c, // Signed 8-byte
DWRF_EH_PE_signed = 0x08, // Signed flag
/* Reference type encodings */
DWRF_EH_PE_pcrel = 0x10, // PC-relative
DWRF_EH_PE_textrel = 0x20, // Text-relative
DWRF_EH_PE_datarel = 0x30, // Data-relative
DWRF_EH_PE_funcrel = 0x40, // Function-relative
DWRF_EH_PE_aligned = 0x50, // Aligned
DWRF_EH_PE_indirect = 0x80 // Indirect
};
/* Additional DWARF constants for debug information */
enum { DWRF_TAG_compile_unit = 0x11 };
enum { DWRF_children_no = 0, DWRF_children_yes = 1 };
enum {
DWRF_AT_name = 0x03, // Name attribute
DWRF_AT_stmt_list = 0x10, // Statement list
DWRF_AT_low_pc = 0x11, // Low PC address
DWRF_AT_high_pc = 0x12 // High PC address
};
enum {
DWRF_FORM_addr = 0x01, // Address form
DWRF_FORM_data4 = 0x06, // 4-byte data
DWRF_FORM_string = 0x08 // String form
};
/* Line number program opcodes */
enum {
DWRF_LNS_extended_op = 0, // Extended opcode
DWRF_LNS_copy = 1, // Copy operation
DWRF_LNS_advance_pc = 2, // Advance program counter
DWRF_LNS_advance_line = 3 // Advance line number
};
/* Line number extended opcodes */
enum {
DWRF_LNE_end_sequence = 1, // End of sequence
DWRF_LNE_set_address = 2 // Set address
};
/*
* Architecture-specific DWARF register numbers
*
* These constants define the register numbering scheme used by DWARF
* for each supported architecture. The numbers must match the ABI
* specification for proper stack unwinding.
*/
enum {
#ifdef __x86_64__
/* x86_64 register numbering (note: order is defined by x86_64 ABI) */
DWRF_REG_AX, // RAX
DWRF_REG_DX, // RDX
DWRF_REG_CX, // RCX
DWRF_REG_BX, // RBX
DWRF_REG_SI, // RSI
DWRF_REG_DI, // RDI
DWRF_REG_BP, // RBP
DWRF_REG_SP, // RSP
DWRF_REG_8, // R8
DWRF_REG_9, // R9
DWRF_REG_10, // R10
DWRF_REG_11, // R11
DWRF_REG_12, // R12
DWRF_REG_13, // R13
DWRF_REG_14, // R14
DWRF_REG_15, // R15
DWRF_REG_RA, // Return address (RIP)
#elif defined(__aarch64__) && defined(__AARCH64EL__) && !defined(__ILP32__)
/* AArch64 register numbering */
DWRF_REG_FP = 29, // Frame Pointer
DWRF_REG_RA = 30, // Link register (return address)
DWRF_REG_SP = 31, // Stack pointer
#else
# error "Unsupported target architecture"
#endif
};
/* DWARF encoding constants used in EH frame headers */
static const uint8_t DwarfUData4 = 0x03; // Unsigned 4-byte data
static const uint8_t DwarfSData4 = 0x0b; // Signed 4-byte data
static const uint8_t DwarfPcRel = 0x10; // PC-relative encoding
static const uint8_t DwarfDataRel = 0x30; // Data-relative encoding
// =============================================================================
// ELF OBJECT CONTEXT
// =============================================================================
/*
* Context for building ELF/DWARF structures
*
* This structure maintains state while constructing DWARF unwind information.
* It acts as a simple buffer manager with pointers to track current position
* and important landmarks within the buffer.
*/
typedef struct ELFObjectContext {
uint8_t* p; // Current write position in buffer
uint8_t* startp; // Start of buffer (for offset calculations)
uint8_t* eh_frame_p; // Start of EH frame data (for relative offsets)
uint32_t code_size; // Size of the code being described
} ELFObjectContext;
/*
* EH Frame Header structure for DWARF unwinding
*
* This structure provides metadata about the DWARF unwinding information
* that follows. It's required by the perf jitdump format to enable proper
* stack unwinding during profiling.
*/
typedef struct {
unsigned char version; // EH frame version (always 1)
unsigned char eh_frame_ptr_enc; // Encoding of EH frame pointer
unsigned char fde_count_enc; // Encoding of FDE count
unsigned char table_enc; // Encoding of table entries
int32_t eh_frame_ptr; // Pointer to EH frame data
int32_t eh_fde_count; // Number of FDEs (Frame Description Entries)
int32_t from; // Start address of code range
int32_t to; // End address of code range
} EhFrameHeader;
// =============================================================================
// DWARF GENERATION UTILITIES
// =============================================================================
/*
* Append a null-terminated string to the ELF context buffer
*
* Args:
* ctx: ELF object context
* str: String to append (must be null-terminated)
*
* Returns: Offset from start of buffer where string was written
*/
static uint32_t elfctx_append_string(ELFObjectContext* ctx, const char* str) {
uint8_t* p = ctx->p;
uint32_t ofs = (uint32_t)(p - ctx->startp);
/* Copy string including null terminator */
do {
*p++ = (uint8_t)*str;
} while (*str++);
ctx->p = p;
return ofs;
}
/*
* Append a SLEB128 (Signed Little Endian Base 128) value
*
* SLEB128 is a variable-length encoding used extensively in DWARF.
* It efficiently encodes small numbers in fewer bytes.
*
* Args:
* ctx: ELF object context
* v: Signed value to encode
*/
static void elfctx_append_sleb128(ELFObjectContext* ctx, int32_t v) {
uint8_t* p = ctx->p;
/* Encode 7 bits at a time, with continuation bit in MSB */
for (; (uint32_t)(v + 0x40) >= 0x80; v >>= 7) {
*p++ = (uint8_t)((v & 0x7f) | 0x80); // Set continuation bit
}
*p++ = (uint8_t)(v & 0x7f); // Final byte without continuation bit
ctx->p = p;
}
/*
* Append a ULEB128 (Unsigned Little Endian Base 128) value
*
* Similar to SLEB128 but for unsigned values.
*
* Args:
* ctx: ELF object context
* v: Unsigned value to encode
*/
static void elfctx_append_uleb128(ELFObjectContext* ctx, uint32_t v) {
uint8_t* p = ctx->p;
/* Encode 7 bits at a time, with continuation bit in MSB */
for (; v >= 0x80; v >>= 7) {
*p++ = (char)((v & 0x7f) | 0x80); // Set continuation bit
}
*p++ = (char)v; // Final byte without continuation bit
ctx->p = p;
}
/*
* Macros for generating DWARF structures
*
* These macros provide a convenient way to write various data types
* to the DWARF buffer while automatically advancing the pointer.
*/
#define DWRF_U8(x) (*p++ = (x)) // Write unsigned 8-bit
#define DWRF_I8(x) (*(int8_t*)p = (x), p++) // Write signed 8-bit
#define DWRF_U16(x) (*(uint16_t*)p = (x), p += 2) // Write unsigned 16-bit
#define DWRF_U32(x) (*(uint32_t*)p = (x), p += 4) // Write unsigned 32-bit
#define DWRF_ADDR(x) (*(uintptr_t*)p = (x), p += sizeof(uintptr_t)) // Write address
#define DWRF_UV(x) (ctx->p = p, elfctx_append_uleb128(ctx, (x)), p = ctx->p) // Write ULEB128
#define DWRF_SV(x) (ctx->p = p, elfctx_append_sleb128(ctx, (x)), p = ctx->p) // Write SLEB128
#define DWRF_STR(str) (ctx->p = p, elfctx_append_string(ctx, (str)), p = ctx->p) // Write string
/* Align to specified boundary with NOP instructions */
#define DWRF_ALIGNNOP(s) \
while ((uintptr_t)p & ((s)-1)) { \
*p++ = DWRF_CFA_nop; \
}
/* Write a DWARF section with automatic size calculation */
#define DWRF_SECTION(name, stmt) \
{ \
uint32_t* szp_##name = (uint32_t*)p; \
p += 4; \
stmt; \
*szp_##name = (uint32_t)((p - (uint8_t*)szp_##name) - 4); \
}
// =============================================================================
// DWARF EH FRAME GENERATION
// =============================================================================
/*
* Initialize DWARF .eh_frame section for a code region
*
* The .eh_frame section contains Call Frame Information (CFI) that describes
* how to unwind the stack at any point in the code. This is essential for
* proper profiling as it allows perf to generate accurate call graphs.
*
* The function generates two main components:
* 1. CIE (Common Information Entry) - describes calling conventions
* 2. FDE (Frame Description Entry) - describes specific function unwinding
*
* Args:
* ctx: ELF object context containing code size and buffer pointers
*/
static void elf_init_ehframe(ELFObjectContext* ctx) {
uint8_t* p = ctx->p;
uint8_t* framep = p; // Remember start of frame data
/*
* DWARF Unwind Table for Trampoline Function
*
* This section defines DWARF Call Frame Information (CFI) using encoded macros
* like `DWRF_U8`, `DWRF_UV`, and `DWRF_SECTION` to describe how the trampoline function
* preserves and restores registers. This is used by profiling tools (e.g., `perf`)
* and debuggers for stack unwinding in JIT-compiled code.
*
* -------------------------------------------------
* TO REGENERATE THIS TABLE FROM GCC OBJECTS:
* -------------------------------------------------
*
* 1. Create a trampoline source file (e.g., `trampoline.c`):
*
* #include <Python.h>
* typedef PyObject* (*py_evaluator)(void*, void*, int);
* PyObject* trampoline(void *ts, void *f, int throwflag, py_evaluator evaluator) {
* return evaluator(ts, f, throwflag);
* }
*
* 2. Compile to an object file with frame pointer preservation:
*
* gcc trampoline.c -I. -I./Include -O2 -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -c
*
* 3. Extract DWARF unwind info from the object file:
*
* readelf -w trampoline.o
*
* Example output from `.eh_frame`:
*
* 00000000 CIE
* Version: 1
* Augmentation: "zR"
* Code alignment factor: 4
* Data alignment factor: -8
* Return address column: 30
* DW_CFA_def_cfa: r31 (sp) ofs 0
*
* 00000014 FDE cie=00000000 pc=0..14
* DW_CFA_advance_loc: 4
* DW_CFA_def_cfa_offset: 16
* DW_CFA_offset: r29 at cfa-16
* DW_CFA_offset: r30 at cfa-8
* DW_CFA_advance_loc: 12
* DW_CFA_restore: r30
* DW_CFA_restore: r29
* DW_CFA_def_cfa_offset: 0
*
* -- These values can be verified by comparing with `readelf -w` or `llvm-dwarfdump --eh-frame`.
*
* ----------------------------------
* HOW TO TRANSLATE TO DWRF_* MACROS:
* ----------------------------------
*
* After compiling your trampoline with:
*
* gcc trampoline.c -I. -I./Include -O2 -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -c
*
* run:
*
* readelf -w trampoline.o
*
* to inspect the generated `.eh_frame` data. You will see two main components:
*
* 1. A CIE (Common Information Entry): shared configuration used by all FDEs.
* 2. An FDE (Frame Description Entry): function-specific unwind instructions.
*
* ---------------------
* Translating the CIE:
* ---------------------
* From `readelf -w`, you might see:
*
* 00000000 0000000000000010 00000000 CIE
* Version: 1
* Augmentation: "zR"
* Code alignment factor: 4
* Data alignment factor: -8
* Return address column: 30
* Augmentation data: 1b
* DW_CFA_def_cfa: r31 (sp) ofs 0
*
* Map this to:
*
* DWRF_SECTION(CIE,
* DWRF_U32(0); // CIE ID (always 0 for CIEs)
* DWRF_U8(DWRF_CIE_VERSION); // Version: 1
* DWRF_STR("zR"); // Augmentation string "zR"
* DWRF_UV(4); // Code alignment factor = 4
* DWRF_SV(-8); // Data alignment factor = -8
* DWRF_U8(DWRF_REG_RA); // Return address register (e.g., x30 = 30)
* DWRF_UV(1); // Augmentation data length = 1
* DWRF_U8(DWRF_EH_PE_pcrel | DWRF_EH_PE_sdata4); // Encoding for FDE pointers
*
* DWRF_U8(DWRF_CFA_def_cfa); // DW_CFA_def_cfa
* DWRF_UV(DWRF_REG_SP); // Register: SP (r31)
* DWRF_UV(0); // Offset = 0
*
* DWRF_ALIGNNOP(sizeof(uintptr_t)); // Align to pointer size boundary
* )
*
* Notes:
* - Use `DWRF_UV` for unsigned LEB128, `DWRF_SV` for signed LEB128.
* - `DWRF_REG_RA` and `DWRF_REG_SP` are architecture-defined constants.
*
* ---------------------
* Translating the FDE:
* ---------------------
* From `readelf -w`:
*
* 00000014 0000000000000020 00000018 FDE cie=00000000 pc=0000000000000000..0000000000000014
* DW_CFA_advance_loc: 4
* DW_CFA_def_cfa_offset: 16
* DW_CFA_offset: r29 at cfa-16
* DW_CFA_offset: r30 at cfa-8
* DW_CFA_advance_loc: 12
* DW_CFA_restore: r30
* DW_CFA_restore: r29
* DW_CFA_def_cfa_offset: 0
*
* Map the FDE header and instructions to:
*
* DWRF_SECTION(FDE,
* DWRF_U32((uint32_t)(p - framep)); // Offset to CIE (relative from here)
* DWRF_U32(-0x30); // Initial PC-relative location of the code
* DWRF_U32(ctx->code_size); // Code range covered by this FDE
* DWRF_U8(0); // Augmentation data length (none)
*
* DWRF_U8(DWRF_CFA_advance_loc | 1); // Advance location by 1 unit (1 * 4 = 4 bytes)
* DWRF_U8(DWRF_CFA_def_cfa_offset); // CFA = SP + 16
* DWRF_UV(16);
*
* DWRF_U8(DWRF_CFA_offset | DWRF_REG_FP); // Save x29 (frame pointer)
* DWRF_UV(2); // At offset 2 * 8 = 16 bytes
*
* DWRF_U8(DWRF_CFA_offset | DWRF_REG_RA); // Save x30 (return address)
* DWRF_UV(1); // At offset 1 * 8 = 8 bytes
*
* DWRF_U8(DWRF_CFA_advance_loc | 3); // Advance location by 3 units (3 * 4 = 12 bytes)
*
* DWRF_U8(DWRF_CFA_offset | DWRF_REG_RA); // Restore x30
* DWRF_U8(DWRF_CFA_offset | DWRF_REG_FP); // Restore x29
*
* DWRF_U8(DWRF_CFA_def_cfa_offset); // CFA = SP
* DWRF_UV(0);
* )
*
* To regenerate:
* 1. Get the `code alignment factor`, `data alignment factor`, and `RA column` from the CIE.
* 2. Note the range of the function from the FDE's `pc=...` line and map it to the JIT code as
* the code is in a different address space every time.
* 3. For each `DW_CFA_*` entry, use the corresponding `DWRF_*` macro:
* - `DW_CFA_def_cfa_offset` → DWRF_U8(DWRF_CFA_def_cfa_offset), DWRF_UV(value)
* - `DW_CFA_offset: rX` → DWRF_U8(DWRF_CFA_offset | reg), DWRF_UV(offset)
* - `DW_CFA_restore: rX` → DWRF_U8(DWRF_CFA_offset | reg) // restore is same as reusing offset
* - `DW_CFA_advance_loc: N` → DWRF_U8(DWRF_CFA_advance_loc | (N / code_alignment_factor))
* 4. Use `DWRF_REG_FP`, `DWRF_REG_RA`, etc., for register numbers.
* 5. Use `sizeof(uintptr_t)` (typically 8) for pointer size calculations and alignment.
*/
/*
* Emit DWARF EH CIE (Common Information Entry)
*
* The CIE describes the calling conventions and basic unwinding rules
* that apply to all functions in this compilation unit.
*/
DWRF_SECTION(CIE,
DWRF_U32(0); // CIE ID (0 indicates this is a CIE)
DWRF_U8(DWRF_CIE_VERSION); // CIE version (1)
DWRF_STR("zR"); // Augmentation string ("zR" = has LSDA)
DWRF_UV(1); // Code alignment factor
DWRF_SV(-(int64_t)sizeof(uintptr_t)); // Data alignment factor (negative)
DWRF_U8(DWRF_REG_RA); // Return address register number
DWRF_UV(1); // Augmentation data length
DWRF_U8(DWRF_EH_PE_pcrel | DWRF_EH_PE_sdata4); // FDE pointer encoding
/* Initial CFI instructions - describe default calling convention */
DWRF_U8(DWRF_CFA_def_cfa); // Define CFA (Call Frame Address)
DWRF_UV(DWRF_REG_SP); // CFA = SP register
DWRF_UV(sizeof(uintptr_t)); // CFA = SP + pointer_size
DWRF_U8(DWRF_CFA_offset|DWRF_REG_RA); // Return address is saved
DWRF_UV(1); // At offset 1 from CFA
DWRF_ALIGNNOP(sizeof(uintptr_t)); // Align to pointer boundary
)
ctx->eh_frame_p = p; // Remember start of FDE data
/*
* Emit DWARF EH FDE (Frame Description Entry)
*
* The FDE describes unwinding information specific to this function.
* It references the CIE and provides function-specific CFI instructions.
*/
DWRF_SECTION(FDE,
DWRF_U32((uint32_t)(p - framep)); // Offset to CIE (backwards reference)
DWRF_U32(-0x30); // Machine code offset relative to .text
DWRF_U32(ctx->code_size); // Address range covered by this FDE (code lenght)
DWRF_U8(0); // Augmentation data length (none)
/*
* Architecture-specific CFI instructions
*
* These instructions describe how registers are saved and restored
* during function calls. Each architecture has different calling
* conventions and register usage patterns.
*/
#ifdef __x86_64__
/* x86_64 calling convention unwinding rules */
# if defined(__CET__) && (__CET__ & 1)
DWRF_U8(DWRF_CFA_advance_loc | 8); // Advance location by 8 bytes when CET protection is enabled
# else
DWRF_U8(DWRF_CFA_advance_loc | 4); // Advance location by 4 bytes
# endif
DWRF_U8(DWRF_CFA_def_cfa_offset); // Redefine CFA offset
DWRF_UV(16); // New offset: SP + 16
DWRF_U8(DWRF_CFA_advance_loc | 6); // Advance location by 6 bytes
DWRF_U8(DWRF_CFA_def_cfa_offset); // Redefine CFA offset
DWRF_UV(8); // New offset: SP + 8
#elif defined(__aarch64__) && defined(__AARCH64EL__) && !defined(__ILP32__)
/* AArch64 calling convention unwinding rules */
DWRF_U8(DWRF_CFA_advance_loc | 1); // Advance location by 1 instruction (stp x29, x30)
DWRF_U8(DWRF_CFA_def_cfa_offset); // Redefine CFA offset
DWRF_UV(16); // CFA = SP + 16 (stack pointer after push)
DWRF_U8(DWRF_CFA_offset | DWRF_REG_FP); // Frame pointer (x29) saved
DWRF_UV(2); // At offset 2 from CFA (2 * 8 = 16 bytes)
DWRF_U8(DWRF_CFA_offset | DWRF_REG_RA); // Link register (x30) saved
DWRF_UV(1); // At offset 1 from CFA (1 * 8 = 8 bytes)
DWRF_U8(DWRF_CFA_advance_loc | 3); // Advance by 3 instructions (mov x16, x3; mov x29, sp; ldp...)
DWRF_U8(DWRF_CFA_offset | DWRF_REG_FP); // Restore frame pointer (x29)
DWRF_U8(DWRF_CFA_offset | DWRF_REG_RA); // Restore link register (x30)
DWRF_U8(DWRF_CFA_def_cfa_offset); // Final CFA adjustment
DWRF_UV(0); // CFA = SP + 0 (stack restored)
#else
# error "Unsupported target architecture"
#endif
DWRF_ALIGNNOP(sizeof(uintptr_t)); // Align to pointer boundary
)
ctx->p = p; // Update context pointer to end of generated data
}
// =============================================================================
// JITDUMP INITIALIZATION
// =============================================================================
/*
* Initialize the perf jitdump interface
*
* This function sets up everything needed to generate jitdump files:
* 1. Creates the jitdump file with a unique name
* 2. Maps the first page to signal perf that we're using the interface
* 3. Writes the jitdump header
* 4. Initializes synchronization primitives
*
* The memory mapping is crucial - perf detects jitdump files by scanning
* for processes that have mapped files matching the pattern /tmp/jit-*.dump
*
* Returns: Pointer to initialized state, or NULL on failure
*/
static void* perf_map_jit_init(void) {
char filename[100];
int pid = getpid();
/* Create unique filename based on process ID */
snprintf(filename, sizeof(filename) - 1, "/tmp/jit-%d.dump", pid);
/* Create/open the jitdump file with appropriate permissions */
const int fd = open(filename, O_CREAT | O_TRUNC | O_RDWR, 0666);
if (fd == -1) {
return NULL; // Failed to create file
}
/* Get system page size for memory mapping */
const long page_size = sysconf(_SC_PAGESIZE);
if (page_size == -1) {
close(fd);
return NULL; // Failed to get page size
}
/*
* Map the first page of the jitdump file
*
* This memory mapping serves as a signal to perf that this process
* is generating JIT code. Perf scans /proc/.../maps looking for mapped
* files that match the jitdump naming pattern.
*
* The mapping must be PROT_READ | PROT_EXEC to be detected by perf.
*/
perf_jit_map_state.mapped_buffer = mmap(
NULL, // Let kernel choose address
page_size, // Map one page
PROT_READ | PROT_EXEC, // Read and execute permissions (required by perf)
MAP_PRIVATE, // Private mapping
fd, // File descriptor
0 // Offset 0 (first page)
);
if (perf_jit_map_state.mapped_buffer == NULL) {
close(fd);
return NULL; // Memory mapping failed
}
perf_jit_map_state.mapped_size = page_size;
/* Convert file descriptor to FILE* for easier I/O operations */
perf_jit_map_state.perf_map = fdopen(fd, "w+");
if (perf_jit_map_state.perf_map == NULL) {
close(fd);
return NULL; // Failed to create FILE*
}
/*
* Set up file buffering for better performance
*
* We use a large buffer (2MB) because jitdump files can be written
* frequently during program execution. Buffering reduces system call
* overhead and improves overall performance.
*/
setvbuf(perf_jit_map_state.perf_map, NULL, _IOFBF, 2 * MB);
/* Write the jitdump file header */
perf_map_jit_write_header(pid, perf_jit_map_state.perf_map);
/*
* Initialize thread synchronization lock
*
* Multiple threads may attempt to write to the jitdump file
* simultaneously. This lock ensures thread-safe access to the
* global jitdump state.
*/
perf_jit_map_state.map_lock = PyThread_allocate_lock();
if (perf_jit_map_state.map_lock == NULL) {
fclose(perf_jit_map_state.perf_map);
return NULL; // Failed to create lock
}
/* Initialize code ID counter */
perf_jit_map_state.code_id = 0;
/* Configure trampoline API with padding information */
trampoline_api.code_padding = PERF_JIT_CODE_PADDING;
return &perf_jit_map_state;
}
// =============================================================================
// MAIN JITDUMP ENTRY WRITING
// =============================================================================
/*
* Write a complete jitdump entry for a Python function
*
* This is the main function called by Python's trampoline system whenever
* a new piece of JIT-compiled code needs to be recorded. It writes both
* the unwinding information and the code load event to the jitdump file.
*
* The function performs these steps:
* 1. Initialize jitdump system if not already done
* 2. Extract function name and filename from Python code object
* 3. Generate DWARF unwinding information
* 4. Write unwinding info event to jitdump file
* 5. Write code load event to jitdump file
*
* Args:
* state: Jitdump state (currently unused, uses global state)
* code_addr: Address where the compiled code resides
* code_size: Size of the compiled code in bytes
* co: Python code object containing metadata
*
* IMPORTANT: This function signature is part of Python's internal API
* and must not be changed without coordinating with core Python development.
*/
static void perf_map_jit_write_entry(void *state, const void *code_addr,
unsigned int code_size, PyCodeObject *co)
{
/* Initialize jitdump system on first use */
if (perf_jit_map_state.perf_map == NULL) {
void* ret = perf_map_jit_init();
if(ret == NULL){
return; // Initialization failed, silently abort
}
}
/*
* Extract function information from Python code object
*
* We create a human-readable function name by combining the qualified
* name (includes class/module context) with the filename. This helps
* developers identify functions in perf reports.
*/
const char *entry = "";
if (co->co_qualname != NULL) {
entry = PyUnicode_AsUTF8(co->co_qualname);
}
const char *filename = "";
if (co->co_filename != NULL) {
filename = PyUnicode_AsUTF8(co->co_filename);
}
/*
* Create formatted function name for perf display
*
* Format: "py::<function_name>:<filename>"
* The "py::" prefix helps identify Python functions in mixed-language
* profiles (e.g., when profiling C extensions alongside Python code).
*/
size_t perf_map_entry_size = snprintf(NULL, 0, "py::%s:%s", entry, filename) + 1;
char* perf_map_entry = (char*) PyMem_RawMalloc(perf_map_entry_size);
if (perf_map_entry == NULL) {
return; // Memory allocation failed
}
snprintf(perf_map_entry, perf_map_entry_size, "py::%s:%s", entry, filename);
const size_t name_length = strlen(perf_map_entry);
uword base = (uword)code_addr;
uword size = code_size;
/*
* Generate DWARF unwinding information
*
* DWARF data is essential for proper stack unwinding during profiling.
* Without it, perf cannot generate accurate call graphs, especially
* in optimized code where frame pointers may be omitted.
*/
ELFObjectContext ctx;
char buffer[1024]; // Buffer for DWARF data (1KB should be sufficient)
ctx.code_size = code_size;
ctx.startp = ctx.p = (uint8_t*)buffer;
/* Generate EH frame (Exception Handling frame) data */
elf_init_ehframe(&ctx);
int eh_frame_size = ctx.p - ctx.startp;
/*
* Write Code Unwinding Information Event
*
* This event must be written before the code load event to ensure
* perf has the unwinding information available when it processes
* the code region.
*/
CodeUnwindingInfoEvent ev2;
ev2.base.event = PerfUnwindingInfo;
ev2.base.time_stamp = get_current_monotonic_ticks();
ev2.unwind_data_size = sizeof(EhFrameHeader) + eh_frame_size;
/* Verify we don't exceed our padding budget */
assert(ev2.unwind_data_size <= PERF_JIT_CODE_PADDING);
ev2.eh_frame_hdr_size = sizeof(EhFrameHeader);
ev2.mapped_size = round_up(ev2.unwind_data_size, 16); // 16-byte alignment
/* Calculate total event size with padding */
int content_size = sizeof(ev2) + sizeof(EhFrameHeader) + eh_frame_size;
int padding_size = round_up(content_size, 8) - content_size; // 8-byte align
ev2.base.size = content_size + padding_size;
/* Write the unwinding info event header */
perf_map_jit_write_fully(&ev2, sizeof(ev2));
/*
* Write EH Frame Header
*
* The EH frame header provides metadata about the DWARF unwinding
* information that follows. It includes pointers and counts that
* help perf navigate the unwinding data efficiently.
*/
EhFrameHeader f;
f.version = 1;
f.eh_frame_ptr_enc = DwarfSData4 | DwarfPcRel; // PC-relative signed 4-byte
f.fde_count_enc = DwarfUData4; // Unsigned 4-byte count
f.table_enc = DwarfSData4 | DwarfDataRel; // Data-relative signed 4-byte
/* Calculate relative offsets for EH frame navigation */
f.eh_frame_ptr = -(eh_frame_size + 4 * sizeof(unsigned char));
f.eh_fde_count = 1; // We generate exactly one FDE per function
f.from = -(round_up(code_size, 8) + eh_frame_size);
int cie_size = ctx.eh_frame_p - ctx.startp;
f.to = -(eh_frame_size - cie_size);
/* Write EH frame data and header */
perf_map_jit_write_fully(ctx.startp, eh_frame_size);
perf_map_jit_write_fully(&f, sizeof(f));
/* Write padding to maintain alignment */
char padding_bytes[] = "\0\0\0\0\0\0\0\0";
perf_map_jit_write_fully(&padding_bytes, padding_size);
/*
* Write Code Load Event
*
* This event tells perf about the new code region. It includes:
* - Memory addresses and sizes
* - Process and thread identification
* - Function name for symbol resolution
* - The actual machine code bytes
*/
CodeLoadEvent ev;
ev.base.event = PerfLoad;
ev.base.size = sizeof(ev) + (name_length+1) + size;
ev.base.time_stamp = get_current_monotonic_ticks();
ev.process_id = getpid();
ev.thread_id = syscall(SYS_gettid); // Get thread ID via system call
ev.vma = base; // Virtual memory address
ev.code_address = base; // Same as VMA for our use case
ev.code_size = size;
/* Assign unique code ID and increment counter */
perf_jit_map_state.code_id += 1;
ev.code_id = perf_jit_map_state.code_id;
/* Write code load event and associated data */
perf_map_jit_write_fully(&ev, sizeof(ev));
perf_map_jit_write_fully(perf_map_entry, name_length+1); // Include null terminator
perf_map_jit_write_fully((void*)(base), size); // Copy actual machine code
/* Clean up allocated memory */
PyMem_RawFree(perf_map_entry);
}
// =============================================================================
// CLEANUP AND FINALIZATION
// =============================================================================
/*
* Finalize and cleanup the perf jitdump system
*
* This function is called when Python is shutting down or when the
* perf trampoline system is being disabled. It ensures all resources
* are properly released and all buffered data is flushed to disk.
*
* Args:
* state: Jitdump state (currently unused, uses global state)
*
* Returns: 0 on success
*
* IMPORTANT: This function signature is part of Python's internal API
* and must not be changed without coordinating with core Python development.
*/
static int perf_map_jit_fini(void* state) {
/*
* Close jitdump file with proper synchronization
*
* We need to acquire the lock to ensure no other threads are
* writing to the file when we close it. This prevents corruption
* and ensures all data is properly flushed.
*/
if (perf_jit_map_state.perf_map != NULL) {
PyThread_acquire_lock(perf_jit_map_state.map_lock, 1);
fclose(perf_jit_map_state.perf_map); // This also flushes buffers
PyThread_release_lock(perf_jit_map_state.map_lock);
/* Clean up synchronization primitive */
PyThread_free_lock(perf_jit_map_state.map_lock);
perf_jit_map_state.perf_map = NULL;
}
/*
* Unmap the memory region
*
* This removes the signal to perf that we were generating JIT code.
* After this point, perf will no longer detect this process as
* having JIT capabilities.
*/
if (perf_jit_map_state.mapped_buffer != NULL) {
munmap(perf_jit_map_state.mapped_buffer, perf_jit_map_state.mapped_size);
perf_jit_map_state.mapped_buffer = NULL;
}
/* Clear global state reference */
trampoline_api.state = NULL;
return 0; // Success
}
// =============================================================================
// PUBLIC API EXPORT
// =============================================================================
/*
* Python Perf Callbacks Structure
*
* This structure defines the callback interface that Python's trampoline
* system uses to integrate with perf profiling. It contains function
* pointers for initialization, event writing, and cleanup.
*
* CRITICAL: This structure and its contents are part of Python's internal
* API. The function signatures and behavior must remain stable to maintain
* compatibility with the Python interpreter's perf integration system.
*
* Used by: Python's _PyPerf_Callbacks system in pycore_ceval.h
*/
_PyPerf_Callbacks _Py_perfmap_jit_callbacks = {
&perf_map_jit_init, // Initialization function
&perf_map_jit_write_entry, // Event writing function
&perf_map_jit_fini, // Cleanup function
};
#endif /* PY_HAVE_PERF_TRAMPOLINE */
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