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If a symbol needs both JUMP_SLOT and GLOB_DAT relocations, there is a minor linker optimization to keep just GLOB_DAT. This optimization is only implemented by GNU ld's x86 port and mold. https://maskray.me/blog/2021-08-29-all-about-global-offset-table#combining-.got-and-.got.plt With the optimizing, the PLT entry is placed in .plt.got and the associated GOTPLT entry is placed in .got (ld.bfd -z now) or .got.plt (ld.bfd -z lazy). The relocation is in .rel[a].dyn. This patch synthesizes `symbol@plt` labels for these .plt.got entries. Example: ``` cat > a.s <<e .globl _start; _start: mov combined0@gotpcrel(%rip), %rax; mov combined1@gotpcrel(%rip), %rax call combined0@plt; call combined1@plt call foo0@plt; call foo1@plt e cat > b.s <<e .globl foo0, foo1, combined0, combined1 foo0: foo1: combined0: combined1: e gcc -fuse-ld=bfd -shared b.s -o b.so gcc -fuse-ld=bfd -pie -nostdlib a.s b.so -o a ``` ``` Disassembly of section .plt: 0000000000001000 <.plt>: 1000: ff 35 ea 1f 00 00 pushq 0x1fea(%rip) # 0x2ff0 <_GLOBAL_OFFSET_TABLE_+0x8> 1006: ff 25 ec 1f 00 00 jmpq *0x1fec(%rip) # 0x2ff8 <_GLOBAL_OFFSET_TABLE_+0x10> 100c: 0f 1f 40 00 nopl (%rax) 0000000000001010 <foo1@plt>: 1010: ff 25 ea 1f 00 00 jmpq *0x1fea(%rip) # 0x3000 <_GLOBAL_OFFSET_TABLE_+0x18> 1016: 68 00 00 00 00 pushq $0x0 101b: e9 e0 ff ff ff jmp 0x1000 <.plt> 0000000000001020 <foo0@plt>: 1020: ff 25 e2 1f 00 00 jmpq *0x1fe2(%rip) # 0x3008 <_GLOBAL_OFFSET_TABLE_+0x20> 1026: 68 01 00 00 00 pushq $0x1 102b: e9 d0 ff ff ff jmp 0x1000 <.plt> Disassembly of section .plt.got: 0000000000001030 <combined0@plt>: 1030: ff 25 a2 1f 00 00 jmpq *0x1fa2(%rip) # 0x2fd8 <foo1+0x2fd8> 1036: 66 90 nop 0000000000001038 <combined1@plt>: 1038: ff 25 a2 1f 00 00 jmpq *0x1fa2(%rip) # 0x2fe0 <foo1+0x2fe0> 103e: 66 90 nop ``` For x86-32, with -z now, if we remove `foo0` and `foo1`, the absence of regular PLT will cause GNU ld to omit .got.plt, and our code cannot synthesize @plt labels. This is an extreme corner case that almost never happens in practice (to trigger the case, ensure every PLT symbol has been taken address). To fix it, we can get the `_GLOBAL_OFFSET_TABLE_` symbol value, but the complexity is not worth it. Close https://github.com/llvm/llvm-project/issues/62537 Reviewed By: bd1976llvm Differential Revision: https://reviews.llvm.org/D149817