https://bugs.llvm.org/show_bug.cgi?id=33096
Bug ID: 33096
Summary: Wrong relocation type in relocatable LTO link
Product: tools
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: gold-plugin
Assignee: unassignedb...@nondot.org
Reporter: eugeni.stepa...@gmail.com
CC: llvm-bugs@lists.llvm.org
Normally, with -fno-PIC, address of external symbol is generated as R_X86_64_64
relocation to that symbol. During the final link the relocation may be
re-written to PLT if the symbol is not resolved.
This does not work when an IR input is used in relocatable link. The output
contains R_X86_64_GOTPCREL relocation.
This does not reproduce with LLD. The problem is specific to gold-plugin.
This is an issue when building linux kernel modules with LTO. The modules are
relocatable object files, and the runtime loader in the kernel does not do
fancy things like GOT or PLT. It expects all text relocations.
$ cat a.c
void f(void);
void *address_of_f(void) {
return &f;
}
BAD CASE:
$ ./bin/clang a.c -c -flto -fno-PIC && ld.gold --plugin lib/LLVMgold.so -r
a.o -o 2.o && objdump -drl 2.o
...
0000000000000000 <address_of_f>:
address_of_f():
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 8b 05 00 00 00 00 mov 0x0(%rip),%rax # b
<address_of_f+0xb>
7: R_X86_64_GOTPCREL f-0x4
b: 5d pop %rbp
c: c3 retq
GOOD CASE:
$ ./bin/clang a.c -c -fno-PIC && ld.gold --plugin lib/LLVMgold.so -r a.o -o
2.o && objdump -drl 2.o
...
0000000000000000 <address_of_f>:
address_of_f():
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 b8 00 00 00 00 00 movabs $0x0,%rax
b: 00 00 00
6: R_X86_64_64 f
e: 5d pop %rbp
f: c3 retq
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