linux/tools/arch
Linus Torvalds 4356e9f841 work around gcc bugs with 'asm goto' with outputs
We've had issues with gcc and 'asm goto' before, and we created a
'asm_volatile_goto()' macro for that in the past: see commits
3f0116c323 ("compiler/gcc4: Add quirk for 'asm goto' miscompilation
bug") and a9f180345f ("compiler/gcc4: Make quirk for
asm_volatile_goto() unconditional").

Then, much later, we ended up removing the workaround in commit
43c249ea0b ("compiler-gcc.h: remove ancient workaround for gcc PR
58670") because we no longer supported building the kernel with the
affected gcc versions, but we left the macro uses around.

Now, Sean Christopherson reports a new version of a very similar
problem, which is fixed by re-applying that ancient workaround.  But the
problem in question is limited to only the 'asm goto with outputs'
cases, so instead of re-introducing the old workaround as-is, let's
rename and limit the workaround to just that much less common case.

It looks like there are at least two separate issues that all hit in
this area:

 (a) some versions of gcc don't mark the asm goto as 'volatile' when it
     has outputs:

        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98619
        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110420

     which is easy to work around by just adding the 'volatile' by hand.

 (b) Internal compiler errors:

        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110422

     which are worked around by adding the extra empty 'asm' as a
     barrier, as in the original workaround.

but the problem Sean sees may be a third thing since it involves bad
code generation (not an ICE) even with the manually added 'volatile'.

but the same old workaround works for this case, even if this feels a
bit like voodoo programming and may only be hiding the issue.

Reported-and-tested-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/all/20240208220604.140859-1-seanjc@google.com/
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Uros Bizjak <ubizjak@gmail.com>
Cc: Jakub Jelinek <jakub@redhat.com>
Cc: Andrew Pinski <quic_apinski@quicinc.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2024-02-09 15:57:48 -08:00
..
alpha/include
arc/include/uapi/asm tools arch uapi: Copy missing unistd.h headers for arc, hexagon and riscv 2019-05-02 16:00:20 -04:00
arm/include tools headers kvm: Sync kvm headers with the kernel sources 2019-12-02 12:54:13 -03:00
arm64 perf build: Ensure sysreg-defs Makefile respects output dir 2023-11-22 11:17:53 -08:00
csky/include/uapi/asm csky: Add support for libdw 2019-05-15 16:36:46 -03:00
hexagon/include/uapi/asm tools arch: Remove uapi bitsperlong.h of hexagon and microblaze 2023-06-22 17:04:37 +02:00
loongarch/include/uapi/asm asm-generic: Unify uapi bitsperlong.h for arm64, riscv and loongarch 2023-06-22 17:04:36 +02:00
microblaze/include/uapi/asm tools arch: Remove uapi bitsperlong.h of hexagon and microblaze 2023-06-22 17:04:37 +02:00
mips/include perf tools: Copy uapi/asm/perf_regs.h from the kernel for MIPS 2021-06-01 10:07:46 -03:00
parisc/include/uapi/asm parisc: Drop the HP-UX ENOSYM and EREMOTERELEASE error codes 2023-11-25 09:43:18 +01:00
powerpc/include perf powerpc: Add support to expose instruction and data address registers as part of extended regs 2021-10-25 13:47:42 -03:00
riscv/include/uapi/asm asm-generic: partially revert "Unify uapi bitsperlong.h for arm64, riscv and loongarch" 2023-08-17 14:51:20 +02:00
s390/include tools headers: Update tools's copy of s390/asm headers 2023-11-22 10:57:47 -08:00
sh/include sh: remove sh5 support 2020-06-01 14:48:52 -04:00
sparc/include tools headers UAPI: Update tools's copy of mman.h headers 2019-07-29 09:02:58 -03:00
x86 work around gcc bugs with 'asm goto' with outputs 2024-02-09 15:57:48 -08:00
xtensa/include