[lld] [lld][MachO] Support for -interposable (PR #131813)

[John Holdsworth via llvm-commits]

johnno1962 wrote:

How about this test (before I commit it):
```

# RUN: rm -rf %t; split-file %s %t
# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/2.s -o %t/2.o
# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/3.s -o %t/3.o
# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/main.s -o %t/main.o

# RUN: %lld -arch x86_64 -interposable -lSystem -o %t/main3 %t/main.o %t/2.o %t/3.o
# RUN: objdump -d %t/main3 | FileCheck %s --check-prefix BUNDLE-OBJ
BUNDLE-OBJ: [[#%x,]] <my_user>:
BUNDLE-OBJ: [[#%x,]]: [[#%x,]] [[#%x,]] [[#%x,]] [[#%x,]] [[#%x,]]                  callq    0x[[#%x,]] <dyld_stub_binder+0x[[#%x,]]>
BUNDLE-OBJ: [[#%x,]]: [[#%x,]]                              retq

#--- 2.s
# my_lib: This contains the exported function
.globl my_func
my_func:
  retq

#--- 3.s
# my_user.s: This is the user/caller of the
#            exported function
.text
my_user:
  callq my_func()
  retq

#--- main.s
# main.s: dummy exec/main loads the exported function.
# This is basically a way to say `my_user` should get
# `my_func` from this executable.
.globl _main
.text
 _main:
  retq
```
objdump -d output is:
```
Mac-minii:llvm-project$ objdump -d ./build/tools/lld/test/MachO/Output/interposable.s.tmp/main3

./build/tools/lld/test/MachO/Output/interposable.s.tmp/main3:	file format mach-o 64-bit x86-64

Disassembly of section __TEXT,__text:

00000001000004e8 <_main>:
1000004e8: c3                          	retq

00000001000004e9 <my_func>:
1000004e9: c3                          	retq

00000001000004ea <my_user>:
1000004ea: e8 07 00 00 00              	callq	0x1000004f6 <dyld_stub_binder+0x1000004f6>
1000004ef: c3                          	retq

Disassembly of section __TEXT,__stubs:

00000001000004f0 <__stubs>:
1000004f0: ff 25 0a 1b 00 00           	jmpq	*0x1b0a(%rip)           ## 0x100002000 <dyld_stub_binder+0x100002000>
1000004f6: ff 25 0c 1b 00 00           	jmpq	*0x1b0c(%rip)           ## 0x100002008 <dyld_stub_binder+0x100002008>

Disassembly of section __TEXT,__stub_helper:

00000001000004fc <__stub_helper>:
1000004fc: 4c 8d 1d 0d 1b 00 00        	leaq	0x1b0d(%rip), %r11      ## 0x100002010 <__dyld_private>
100000503: 41 53                       	pushq	%r11
100000505: ff 25 f5 0a 00 00           	jmpq	*0xaf5(%rip)            ## 0x100001000 <dyld_stub_binder+0x100001000>
10000050b: 90                          	nop
10000050c: 68 00 00 00 00              	pushq	$0x0
100000511: e9 e6 ff ff ff              	jmp	0x1000004fc <__stub_helper>
100000516: 68 0c 00 00 00              	pushq	$0xc
10000051b: e9 dc ff ff ff              	jmp	0x1000004fc <__stub_helper>


https://github.com/llvm/llvm-project/pull/131813