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Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
2005-04-17 06:20:36 +08:00
/*
[MIPS] cpu-bugs64.c: GCC 3.3 constraint workaround Add a workaround to address warnings generated on the "n" constraint by GCC 3.3 and below. Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2007-09-18 00:11:07 +08:00
* Copyright (C) 2004, 2007 Maciej W. Rozycki
Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
2005-04-17 06:20:36 +08:00
*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*/
#ifndef _ASM_COMPILER_H
#define _ASM_COMPILER_H
MIPS: Workaround GCC __builtin_unreachable reordering bug Some versions of GCC for the MIPS architecture suffer from a bug which can lead to instructions from beyond an unreachable statement being incorrectly reordered into earlier branch delay slots if the unreachable statement is the only content of a case in a switch statement. This can lead to seemingly random behaviour, such as invalid memory accesses from incorrectly reordered loads or stores, and link failures on microMIPS builds. See this potential GCC fix for details: https://gcc.gnu.org/ml/gcc-patches/2015-09/msg00360.html Runtime problems resulting from this bug were initially observed using a maltasmvp_defconfig v4.4 kernel built using GCC 4.9.2 (from a Codescape SDK 2015.06-05 toolchain), with the result being an address exception taken after log messages about the L1 caches (during probe of the L2 cache): Initmem setup node 0 [mem 0x0000000080000000-0x000000009fffffff] VPE topology {2,2} total 4 Primary instruction cache 64kB, VIPT, 4-way, linesize 32 bytes. Primary data cache 64kB, 4-way, PIPT, no aliases, linesize 32 bytes <AdEL exception here> This is early enough that the kernel exception vectors are not in use, so any further output depends upon the bootloader. This is reproducible in QEMU where no further output occurs - ie. the system hangs here. Given the nature of the bug it may potentially be hit with differing symptoms. The bug is known to affect GCC versions as recent as 7.3, and it is unclear whether GCC 8 fixed it or just happens not to encounter the bug in the testcase found at the link above due to differing optimizations. This bug can be worked around by placing a volatile asm statement, which GCC is prevented from reordering past, prior to the __builtin_unreachable call. That was actually done already for other reasons by commit 173a3efd3edb ("bug.h: work around GCC PR82365 in BUG()"), but creates problems for microMIPS builds due to the lack of a .insn directive. The microMIPS ISA allows for interlinking with regular MIPS32 code by repurposing bit 0 of the program counter as an ISA mode bit. To switch modes one changes the value of this bit in the PC. However typical branch instructions encode their offsets as multiples of 2-byte instruction halfwords, which means they cannot change ISA mode - this must be done using either an indirect branch (a jump-register in MIPS terminology) or a dedicated jalx instruction. In order to ensure that regular branches don't attempt to target code in a different ISA which they can't actually switch to, the linker will check that branch targets are code in the same ISA as the branch. Unfortunately our empty asm volatile statements don't qualify as code, and the link for microMIPS builds fails with errors such as: arch/mips/mm/dma-default.s:3265: Error: branch to a symbol in another ISA mode arch/mips/mm/dma-default.s:5027: Error: branch to a symbol in another ISA mode Resolve this by adding a .insn directive within the asm statement which declares that what comes next is code. This may or may not be true, since we don't really know what comes next, but as this code is in an unreachable path anyway that doesn't matter since we won't execute it. We do this in asm/compiler.h & select CONFIG_HAVE_ARCH_COMPILER_H in order to have this included by linux/compiler_types.h after linux/compiler-gcc.h. This will result in asm/compiler.h being included in all C compilations via the -include linux/compiler_types.h argument in c_flags, which should be harmless. Signed-off-by: Paul Burton <paul.burton@mips.com> Fixes: 173a3efd3edb ("bug.h: work around GCC PR82365 in BUG()") Patchwork: https://patchwork.linux-mips.org/patch/20270/ Cc: James Hogan <jhogan@kernel.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: linux-mips@linux-mips.org
2018-08-21 06:36:18 +08:00
/*
* With GCC 4.5 onwards we can use __builtin_unreachable to indicate to the
* compiler that a particular code path will never be hit. This allows it to be
* optimised out of the generated binary.
*
* Unfortunately at least GCC 4.6.3 through 7.3.0 inclusive suffer from a bug
* that can lead to instructions from beyond an unreachable statement being
* incorrectly reordered into earlier delay slots if the unreachable statement
* is the only content of a case in a switch statement. This can lead to
* seemingly random behaviour, such as invalid memory accesses from incorrectly
* reordered loads or stores. See this potential GCC fix for details:
*
* https://gcc.gnu.org/ml/gcc-patches/2015-09/msg00360.html
*
* It is unclear whether GCC 8 onwards suffer from the same issue - nothing
* relevant is mentioned in GCC 8 release notes and nothing obviously relevant
* stands out in GCC commit logs, but these newer GCC versions generate very
* different code for the testcase which doesn't exhibit the bug.
*
* GCC also handles stack allocation suboptimally when calling noreturn
* functions or calling __builtin_unreachable():
*
* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365
*
* We work around both of these issues by placing a volatile asm statement,
* which GCC is prevented from reordering past, prior to __builtin_unreachable
* calls.
*
* The .insn statement is required to ensure that any branches to the
* statement, which sadly must be kept due to the asm statement, are known to
* be branches to code and satisfy linker requirements for microMIPS kernels.
*/
#undef barrier_before_unreachable
#define barrier_before_unreachable() asm volatile(".insn")
MIPS: Simplify GCC_OFF_SMALL_ASM definition The GCC_OFF_SMALL_ASM macro defines the constraint to use for instructions needing "small offsets", typically the LL or SC instructions. Historically these had 16 bit offsets, but microMIPS & MIPS32/MIPS64r6 onwards reduced the width of the offset field. GCC 4.9 & higher supports a ZC constraint which matches the offset requirements of the LL & SC instructions. Where supported we can use the ZC constraint regardless of ISA, and it will handle the requirements of the ISA correctly. As such we require 3 cases: - GCC 4.9 & higher can use ZC. - GCC older than 4.9 must use the older R constraint, which does not take into account microMIPS or MIPSr6. - microMIPS builds therefore require GCC 4.9 or higher. MIPSr6 support was only introduced in newer compilers anyway so it can be ignored here. The current code complicates this a little by specifically having MIPSr6 bypass the GCC version check, and using the R constraint for pre-MIPSr6 builds even if the compiler supports ZC which would be equivalent. Simplify this such that the code straightforwardly implements the 3 cases outlined above. For non-GCC compilers we presume that ZC is safe to use. In practice the only non-GCC compiler of interest is clang and it has supported the ZC constraint since version 3.7.0. It seems safe enough to presume that nobody will expect to built a working kernel using a clang version older than that, and if they do then they'll have bigger problems. As such we don't check the clang version number & just presume ZC is usable when the compiler is not GCC. Signed-off-by: Paul Burton <paul.burton@mips.com> Patchwork: https://patchwork.linux-mips.org/patch/20999/ Cc: linux-mips@linux-mips.org
2018-11-08 07:05:46 +08:00
#if !defined(CONFIG_CC_IS_GCC) || \
(__GNUC__ > 4) || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)
# define GCC_OFF_SMALL_ASM() "ZC"
#elif defined(CONFIG_CPU_MICROMIPS)
# error "microMIPS compilation unsupported with GCC older than 4.9"
MIPS: Fix microMIPS LL/SC immediate offsets In the microMIPS encoding some memory access instructions have their immediate offset reduced to 12 bits only. That does not match the GCC `R' constraint we use in some places to satisfy the requirement, resulting in build failures like this: {standard input}: Assembler messages: {standard input}:720: Error: macro used $at after ".set noat" {standard input}:720: Warning: macro instruction expanded into multiple instructions Fix the problem by defining a macro, `GCC_OFF12_ASM', that expands to the right constraint depending on whether microMIPS or standard MIPS code is produced. Also apply the fix to where `m' is used as in the worst case this change does nothing, e.g. where the pointer was already in a register such as a function argument and no further offset was requested, and in the best case it avoids an extraneous sequence of up to two instructions to load the high 20 bits of the address in the LL/SC loop. This reduces the risk of lock contention that is the higher the more instructions there are in the critical section between LL and SC. Strictly speaking we could just bulk-replace `R' with `ZC' as the latter constraint adjusts automatically depending on the ISA selected. However it was only introduced with GCC 4.9 and we keep supporing older compilers for the standard MIPS configuration, hence the slightly more complicated approach I chose. The choice of a zero-argument function-like rather than an object-like macro was made so that it does not look like a function call taking the C expression used for the constraint as an argument. This is so as not to confuse the reader or formatting checkers like `checkpatch.pl' and follows previous practice. Signed-off-by: Maciej W. Rozycki <macro@codesourcery.com> Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/8482/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2014-11-16 06:08:48 +08:00
#else
MIPS: Simplify GCC_OFF_SMALL_ASM definition The GCC_OFF_SMALL_ASM macro defines the constraint to use for instructions needing "small offsets", typically the LL or SC instructions. Historically these had 16 bit offsets, but microMIPS & MIPS32/MIPS64r6 onwards reduced the width of the offset field. GCC 4.9 & higher supports a ZC constraint which matches the offset requirements of the LL & SC instructions. Where supported we can use the ZC constraint regardless of ISA, and it will handle the requirements of the ISA correctly. As such we require 3 cases: - GCC 4.9 & higher can use ZC. - GCC older than 4.9 must use the older R constraint, which does not take into account microMIPS or MIPSr6. - microMIPS builds therefore require GCC 4.9 or higher. MIPSr6 support was only introduced in newer compilers anyway so it can be ignored here. The current code complicates this a little by specifically having MIPSr6 bypass the GCC version check, and using the R constraint for pre-MIPSr6 builds even if the compiler supports ZC which would be equivalent. Simplify this such that the code straightforwardly implements the 3 cases outlined above. For non-GCC compilers we presume that ZC is safe to use. In practice the only non-GCC compiler of interest is clang and it has supported the ZC constraint since version 3.7.0. It seems safe enough to presume that nobody will expect to built a working kernel using a clang version older than that, and if they do then they'll have bigger problems. As such we don't check the clang version number & just presume ZC is usable when the compiler is not GCC. Signed-off-by: Paul Burton <paul.burton@mips.com> Patchwork: https://patchwork.linux-mips.org/patch/20999/ Cc: linux-mips@linux-mips.org
2018-11-08 07:05:46 +08:00
# define GCC_OFF_SMALL_ASM() "R"
#endif
MIPS: Fix microMIPS LL/SC immediate offsets In the microMIPS encoding some memory access instructions have their immediate offset reduced to 12 bits only. That does not match the GCC `R' constraint we use in some places to satisfy the requirement, resulting in build failures like this: {standard input}: Assembler messages: {standard input}:720: Error: macro used $at after ".set noat" {standard input}:720: Warning: macro instruction expanded into multiple instructions Fix the problem by defining a macro, `GCC_OFF12_ASM', that expands to the right constraint depending on whether microMIPS or standard MIPS code is produced. Also apply the fix to where `m' is used as in the worst case this change does nothing, e.g. where the pointer was already in a register such as a function argument and no further offset was requested, and in the best case it avoids an extraneous sequence of up to two instructions to load the high 20 bits of the address in the LL/SC loop. This reduces the risk of lock contention that is the higher the more instructions there are in the critical section between LL and SC. Strictly speaking we could just bulk-replace `R' with `ZC' as the latter constraint adjusts automatically depending on the ISA selected. However it was only introduced with GCC 4.9 and we keep supporing older compilers for the standard MIPS configuration, hence the slightly more complicated approach I chose. The choice of a zero-argument function-like rather than an object-like macro was made so that it does not look like a function call taking the C expression used for the constraint as an argument. This is so as not to confuse the reader or formatting checkers like `checkpatch.pl' and follows previous practice. Signed-off-by: Maciej W. Rozycki <macro@codesourcery.com> Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/8482/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2014-11-16 06:08:48 +08:00
MIPS: asm: compiler: Add new macros to set ISA and arch asm annotations There are certain places where the code uses .set mips32 or .set mips64 or .set arch=r4000. In preparation of MIPS R6 support, and in order to use as less #ifdefs as possible, we define new macros to set similar annotations for MIPS R6. Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
2014-11-18 23:02:32 +08:00
#ifdef CONFIG_CPU_MIPSR6
#define MIPS_ISA_LEVEL "mips64r6"
#define MIPS_ISA_ARCH_LEVEL MIPS_ISA_LEVEL
#define MIPS_ISA_LEVEL_RAW mips64r6
#define MIPS_ISA_ARCH_LEVEL_RAW MIPS_ISA_LEVEL_RAW
#else
/* MIPS64 is a superset of MIPS32 */
#define MIPS_ISA_LEVEL "mips64r2"
#define MIPS_ISA_ARCH_LEVEL "arch=r4000"
#define MIPS_ISA_LEVEL_RAW mips64r2
#define MIPS_ISA_ARCH_LEVEL_RAW MIPS_ISA_LEVEL_RAW
#endif /* CONFIG_CPU_MIPSR6 */
Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
2005-04-17 06:20:36 +08:00
#endif /* _ASM_COMPILER_H */