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Re: [RFC PATCH 4/4] x86/asm: Use ASM_CALL() macro for inline asm statements with call instructions

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On Thu, Aug 31, 2017 at 04:50:41PM +0200, Peter Zijlstra wrote:
> On Thu, Aug 31, 2017 at 09:11:20AM -0500, Josh Poimboeuf wrote:
> > Inline asm statements which have call instructions can be problematic.
> > GCC doesn't know about the call instructions, so in some cases it can
> > insert the asm before setting up the frame pointer.  This can result in
> > bad stack traces when unwinding from the called function.
> > 
> > Previously we worked around this issue by listing the stack pointer as
> > an input/output constraint for the inline asm.  That works for GCC, but
> > unfortunately it doesn't work for Clang.  In fact, it causes Clang to
> > corrupt the stack pointer.
> 
> Sounds like it ought to get fixed regardless and then it might as well
> do the right thing ;-)

There was some disagreement about what the "right thing" is because it's
an undocumented and unintuitive interface.

And I use the term "interface" loosely.  It was apparently a side effect
which was mentioned to me on the GCC mailing list.

-- 
Josh

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[RFC PATCH 0/4] x86/asm: Add ASM_CALL() macro for inline asms with call instructions Josh Poimboeuf <jpoimboe@redhat.com> - 2017-08-31 16:20 +0200
  [RFC PATCH 3/4] x86/asm: Make alternative macro interfaces more clear and consistent Josh Poimboeuf <jpoimboe@redhat.com> - 2017-08-31 16:20 +0200
    Re: [RFC PATCH 3/4] x86/asm: Make alternative macro interfaces more  clear and consistent Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-31 18:20 +0200
      Re: [RFC PATCH 3/4] x86/asm: Make alternative macro interfaces more  clear and consistent Josh Poimboeuf <jpoimboe@redhat.com> - 2017-08-31 19:30 +0200
        Re: [RFC PATCH 3/4] x86/asm: Make alternative macro interfaces more  clear and consistent Josh Poimboeuf <jpoimboe@redhat.com> - 2017-08-31 19:40 +0200
          Re: [RFC PATCH 3/4] x86/asm: Make alternative macro interfaces more  clear and consistent Ingo Molnar <mingo@kernel.org> - 2017-09-02 12:40 +0200
  [RFC PATCH 2/4] x86/asm: Convert some inline asm positional operands to named operands Josh Poimboeuf <jpoimboe@redhat.com> - 2017-08-31 16:20 +0200
  [RFC PATCH 1/4] x86/paravirt: Fix output constraint macro names Josh Poimboeuf <jpoimboe@redhat.com> - 2017-08-31 16:20 +0200
  [RFC PATCH 4/4] x86/asm: Use ASM_CALL() macro for inline asm statements with call instructions Josh Poimboeuf <jpoimboe@redhat.com> - 2017-08-31 16:20 +0200
    Re: [RFC PATCH 4/4] x86/asm: Use ASM_CALL() macro for inline asm  statements with call instructions Peter Zijlstra <peterz@infradead.org> - 2017-08-31 17:00 +0200
      Re: [RFC PATCH 4/4] x86/asm: Use ASM_CALL() macro for inline asm  statements with call instructions Josh Poimboeuf <jpoimboe@redhat.com> - 2017-08-31 17:30 +0200
        Re: [RFC PATCH 4/4] x86/asm: Use ASM_CALL() macro for inline asm  statements with call instructions Dmitry Vyukov <dvyukov@google.com> - 2017-08-31 17:50 +0200

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