https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=207736
Bug ID: 207736
Summary: clang 3.8.0/powerpc's _Unwind_RaiseException code
generation has messed up r31 (frame pointer)
save/restore code (SEGV's can result)
Product: Base System
Version: 11.0-CURRENT
Hardware: ppc
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: bin
Assignee: freebsd-bugs@FreeBSD.org
Reporter: mar...@dsl-only.net
[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 "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.
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