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libbpf: Switch tracing and CO-RE helper macros to bpf_probe_read_kernel() 

Now that libbpf can automatically fallback to bpf_probe_read() on old kernels
not yet supporting bpf_probe_read_kernel(), switch libbpf BPF-side helper
macros to use appropriate BPF helper for reading kernel data.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/bpf/20200818213356.2629020-7-andriin@fb.com
This commit is contained in:
Andrii Nakryiko 2020-08-18 14:33:55 -07:00 committed by Alexei Starovoitov
parent 02f47faa25
commit 70785cfb19
2 changed files with 24 additions and 20 deletions
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40
tools/lib/bpf/bpf_core_read.h
View File

@ -24,27 +24,29 @@ enum bpf_field_info_kind {
#if __BYTE_ORDER == __LITTLE_ENDIAN
#define __CORE_BITFIELD_PROBE_READ(dst, src, fld) \
bpf_probe_read((void *)dst, \
__CORE_RELO(src, fld, BYTE_SIZE), \
(const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
bpf_probe_read_kernel( \
(void *)dst, \
__CORE_RELO(src, fld, BYTE_SIZE), \
(const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
#else
/* semantics of LSHIFT_64 assumes loading values into low-ordered bytes, so
* for big-endian we need to adjust destination pointer accordingly, based on
* field byte size
*/
#define __CORE_BITFIELD_PROBE_READ(dst, src, fld) \
bpf_probe_read((void *)dst + (8 - __CORE_RELO(src, fld, BYTE_SIZE)), \
__CORE_RELO(src, fld, BYTE_SIZE), \
(const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
bpf_probe_read_kernel( \
(void *)dst + (8 - __CORE_RELO(src, fld, BYTE_SIZE)), \
__CORE_RELO(src, fld, BYTE_SIZE), \
(const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
#endif
/*
* Extract bitfield, identified by s->field, and return its value as u64.
* All this is done in relocatable manner, so bitfield changes such as
* signedness, bit size, offset changes, this will be handled automatically.
* This version of macro is using bpf_probe_read() to read underlying integer
* storage. Macro functions as an expression and its return type is
* bpf_probe_read()'s return value: 0, on success, <0 on error.
* This version of macro is using bpf_probe_read_kernel() to read underlying
* integer storage. Macro functions as an expression and its return type is
* bpf_probe_read_kernel()'s return value: 0, on success, <0 on error.
*/
#define BPF_CORE_READ_BITFIELD_PROBED(s, field) ({ \
unsigned long long val = 0; \
@ -99,8 +101,8 @@ enum bpf_field_info_kind {
__builtin_preserve_field_info(field, BPF_FIELD_BYTE_SIZE)
/*
* bpf_core_read() abstracts away bpf_probe_read() call and captures offset
* relocation for source address using __builtin_preserve_access_index()
* bpf_core_read() abstracts away bpf_probe_read_kernel() call and captures
* offset relocation for source address using __builtin_preserve_access_index()
* built-in, provided by Clang.
*
* __builtin_preserve_access_index() takes as an argument an expression of
@ -115,8 +117,8 @@ enum bpf_field_info_kind {
* (local) BTF, used to record relocation.
*/
#define bpf_core_read(dst, sz, src) \
bpf_probe_read(dst, sz, \
(const void *)__builtin_preserve_access_index(src))
bpf_probe_read_kernel(dst, sz, \
(const void *)__builtin_preserve_access_index(src))
/*
* bpf_core_read_str() is a thin wrapper around bpf_probe_read_str()
@ -124,8 +126,8 @@ enum bpf_field_info_kind {
* argument.
*/
#define bpf_core_read_str(dst, sz, src) \
bpf_probe_read_str(dst, sz, \
(const void *)__builtin_preserve_access_index(src))
bpf_probe_read_kernel_str(dst, sz, \
(const void *)__builtin_preserve_access_index(src))
#define ___concat(a, b) a ## b
#define ___apply(fn, n) ___concat(fn, n)
@ -239,15 +241,17 @@ enum bpf_field_info_kind {
* int x = BPF_CORE_READ(s, a.b.c, d.e, f, g);
*
* BPF_CORE_READ will decompose above statement into 4 bpf_core_read (BPF
* CO-RE relocatable bpf_probe_read() wrapper) calls, logically equivalent to:
* CO-RE relocatable bpf_probe_read_kernel() wrapper) calls, logically
* equivalent to:
* 1. const void *__t = s->a.b.c;
* 2. __t = __t->d.e;
* 3. __t = __t->f;
* 4. return __t->g;
*
* Equivalence is logical, because there is a heavy type casting/preservation
* involved, as well as all the reads are happening through bpf_probe_read()
* calls using __builtin_preserve_access_index() to emit CO-RE relocations.
* involved, as well as all the reads are happening through
* bpf_probe_read_kernel() calls using __builtin_preserve_access_index() to
* emit CO-RE relocations.
*
* N.B. Only up to 9 "field accessors" are supported, which should be more
* than enough for any practical purpose.

4
tools/lib/bpf/bpf_tracing.h
View File

@ -289,9 +289,9 @@ struct pt_regs;
#define BPF_KRETPROBE_READ_RET_IP BPF_KPROBE_READ_RET_IP
#else
#define BPF_KPROBE_READ_RET_IP(ip, ctx) \
({ bpf_probe_read(&(ip), sizeof(ip), (void *)PT_REGS_RET(ctx)); })
({ bpf_probe_read_kernel(&(ip), sizeof(ip), (void *)PT_REGS_RET(ctx)); })
#define BPF_KRETPROBE_READ_RET_IP(ip, ctx) \
({ bpf_probe_read(&(ip), sizeof(ip), \
({ bpf_probe_read_kernel(&(ip), sizeof(ip), \
(void *)(PT_REGS_FP(ctx) + sizeof(ip))); })
#endif