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
