Bug 207736 submitted for TARGET_ARCH=powerpc (& ppc64?) clang 3.8.0 frame-pointer code generation error for _Unwind_RaiseException

[Mark Millard]

[This has been reported on llvm bugzilla: 26856.]

The below causes gdb difficulties for its stack handling: more than just exception handling is at issue. I just happened to notice it via exception handling.

Function _Unwind_RaiseException below is from a FreeBSD TARGET_ARCH=powerpc "buildworld" using clang 3.8.0.

Dump of assembler code for function _Unwind_RaiseException:
   0x41b2ab80 <+0>:	mflr    r0
   0x41b2ab84 <+4>:	stw     r31,-148(r1)
   0x41b2ab88 <+8>:	stw     r30,-152(r1)
   0x41b2ab8c <+12>:	stw     r0,4(r1)
   0x41b2ab90 <+16>:	stwu    r1,-2992(r1)
   0x41b2ab94 <+20>:	mr      r31,r1
. . .
   0x41b2abe0 <+96>:	stw     r31,2844(r31)
(which replaces the earlier save of the old Frame pointer R31
value with a copy of r1's current  value. Note the offset
relationships with the r1 adjustment: -2992+2844=-148)
. . .
   0x41b2add0 <+592>:	lwz     r31,2844(r31)
(This restores the r1 value that resulted from the "stwu r1,-2992(r1)" into R31.)
. . .
   0x41b2ae30 <+688>:	lwz     r31,-148(r1)
(This restores the r1 value that resulted from the "stwu r1,-2992(r1)" into R31.)
. . .

The wrong r31 value is present when _Unwind_RaiseException returns.

But before that while _Unwind_RaiseException is active the C++ exception handling infrastructure has been given bad r31 information for around _Unwind_RaiseException's frame.

===
Mark Millard
markmi at dsl-only.net