linux/tools/include
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
..
asm tools headers: Update the copy of x86's mem{cpy,set}_64.S used in 'perf bench' 2023-05-17 10:42:19 -03:00
asm-generic perf tools headers: update the asm-generic/unaligned.h copy with the kernel sources 2024-01-31 14:02:41 -03:00
io_uring selftests/net: Extract uring helpers to be reusable 2023-10-19 16:42:03 -06:00
linux work around gcc bugs with 'asm goto' with outputs 2024-02-09 15:57:48 -08:00
nolibc tools/nolibc: add support for getrlimit/setrlimit 2023-12-11 22:38:35 +01:00
perf KVM: selftests: aarch64: Update tools copy of arm_pmuv3.h 2023-12-12 09:46:22 +00:00
tools tools include: add dis-asm-compat.h to handle version differences 2022-08-01 15:29:49 -03:00
trace/events
uapi tools include UAPI: Sync linux/mount.h copy with the kernel sources 2024-01-30 11:49:54 -03:00
vdso tools headers: Synchronize {linux,vdso}/bits.h with the kernel sources 2023-03-03 22:34:15 -03:00