https://bugs.llvm.org/show_bug.cgi?id=49004
Bug ID: 49004
Summary: [PPC] Lowering of llvm.init_trampoline problem with
libgcc
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: PowerPC
Assignee: unassignedb...@nondot.org
Reporter: v.chur...@gmail.com
CC: llvm-bugs@lists.llvm.org, nemanja.i....@gmail.com
@llvm.init_trampoline on PPC lowers [1] to a call to `__trampoline_setup` which
IIUC is either defined in libgcc [2] or compiler-rt [3]. As far as I can tell
`compiler-rt` doesn't implement it for powerpc64le, and libgcc has a bug in the
assembly where it checks that the passed `trampoline size` (size of the
allocated buffer) is **smaller** than the required/computed by the linker
`trampoline size`. `r8` contains the trampoline size as calculated by the
linker, and `r4` contains the trampoline size passed in from the outside. LLVM
will always pass 48 as a value on ppc64le, whereas the calculated trampoline
size could vary and on the systems I have access to is `32`.
`libgcc` then does a:
if (r4 < r8)
abort();
[1]
https://github.com/llvm/llvm-project/blob/ffc3e800c65ee58166255ff897f8b7e6d850ddda/llvm/lib/Target/PowerPC/PPCISelLowering.cpp#L3485
[2]
https://github.com/gcc-mirror/gcc/blob/02551aa99960ff6b0d9a44d234b8f6c9b230788c/libgcc/config/rs6000/tramp.S#L150
[3]
https://github.com/llvm/llvm-project/blob/main/compiler-rt/lib/builtins/trampoline_setup.c
I haven't been able to fill a bug against libgcc since account registration is
restricted.
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