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Linus Torvalds f70efe54b9 work around gcc bugs with 'asm goto' with outputs 
commit 68fb3ca0e4 upstream.

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'.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2024-02-23 09:12:28 +01:00
..
boot arc: dts: Harmonize EHCI/OHCI DT nodes name 2022-10-17 16:32:12 -07:00
configs arc: update config files 2022-10-17 16:32:12 -07:00
include work around gcc bugs with 'asm goto' with outputs 2024-02-23 09:12:28 +01:00
kernel ARC: fix spare error 2024-01-20 11:50:08 +01:00
lib
…
mm mm/fault: convert remaining simple cases to lock_mm_and_find_vma() 2023-07-01 13:16:25 +02:00
plat-axs10x arc: Replace lkml.org links with lore 2021-12-28 19:48:49 -08:00
plat-hsdk arc: Replace lkml.org links with lore 2021-12-28 19:48:49 -08:00
plat-sim
…
plat-tb10x
…
Kbuild kbuild: use more subdir- for visiting subdirectories while cleaning 2021-10-24 13:49:46 +09:00
Kconfig mm/fault: convert remaining simple cases to lock_mm_and_find_vma() 2023-07-01 13:16:25 +02:00
Kconfig.debug
…
Makefile kbuild: remove head-y syntax 2022-10-02 18:06:03 +09:00