Centos-kernel-stream-9

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Waiman Long 157e5d51df work around gcc bugs with 'asm goto' with outputs

JIRA: https://redhat.atlassian.net/browse/RHEL-166727
Conflicts:
 1) Hunks with merge conflicts for files missing or in unsupported
    arches are dropped.
 2) The arch/x86/include/asm/cpufeature.h hunk is dropped as the change
    had already been applied as part of RHEL commit 824a2da84f ("x86/asm:
    Use %c/%n instead of %P operand modifier in asm templates").
 3) Two hunks from arch/powerpc/include/asm/uaccess.h are dropped due
    to missing upstream commit dc5dac748af9 ("powerpc/64: Add support
    to build with prefixed instructions").
 4) The arch/powerpc/kernel/irq_64.c hunk is applied to
    arch/powerpc/kernel/irq.c.
 5) A context diff in the include/linux/compiler-gcc.h hunk due to
    missing upstream commit 173a3efd3e ("bug.h: work around GCC
    PR82365 in BUG()").

commit 4356e9f841f7fbb945521cef3577ba394c65f3fc
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 9 Feb 2024 12:39:31 -0800

    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
    43c249ea0b1e ("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>

Signed-off-by: Waiman Long <longman@redhat.com>