lld error "undefined symbol: _GLOBAL_OFFSET_TABLE_ " with LTO

[medhefgo]

The following test file fails with LTO when compiled for x86. Other arches or bfd don't seem to exhibit this.

$ cat clang-bug.c 
void a(void) {}
void _start(void) { a(); }

$ clang -target i386-pc-linux-gnu -fuse-ld=lld -nostdlib -o /dev/null clang-bug.c

$ clang -target i386-pc-linux-gnu -fuse-ld=lld -nostdlib -o /dev/null clang-bug.c -flto
ld.lld: error: undefined symbol: _GLOBAL_OFFSET_TABLE_
>>> referenced by ld-temp.o
>>>               lto.tmp:(_start)
clang-15: error: linker command failed with exit code 1 (use -v to see invocation)

[MaskRay]

Related to #38982

[aeubanks]

similar repro with x86-64 (medium code model with 0 large data threshold uses the GOT as the base register to address globals):

$ cat /tmp/a.c
extern int i;
void _start(void) { i++; }
$ cat /tmp/b.c
int i = 0;
$ clang -fuse-ld=lld -o /dev/null /tmp/a.c /tmp/b.c -nostdlib -Wl,--no-relax -flto=thin -mcmodel=medium -mlarge-data-threshold=0
ld.lld: error: undefined symbol: _GLOBAL_OFFSET_TABLE_
>>> referenced by a.c
>>>               /tmp/null.lto.a-ce4e32.o:(_start)

[MaskRay]

I can take this. I think the best workaround is to synthesize a _GLOBAL_OFFSET_TABLE_ entry in llvm/lib/Object/IRSymtab.cpp . Unfortunately this is different from static const char *PreservedSymbols.