[lkml]   [2017]   [Aug]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [RFC PATCH 4/4] x86/asm: Use ASM_CALL() macro for inline asm statements with call instructions
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.


 \ /
  Last update: 2017-08-31 17:22    [W:0.062 / U:1.992 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site