Clang and _GLOBAL_OFFSET_TABLE_

bar.cpp

unsigned long SOME_GLOBAL = 123;

foo.cpp

extern unsigned long _GLOBAL_OFFSET_TABLE_ [];
extern unsigned long SOME_GLOBAL;

int main() {
    auto foo1 = &_GLOBAL_OFFSET_TABLE_;
    auto foo2 =  _GLOBAL_OFFSET_TABLE_;

    auto bar1 = &SOME_GLOBAL;
    auto bar2 =  SOME_GLOBAL;

    return 0;
}

Makefile

#CC = /home/justin/.local/lib/jsix/toolchains/llvm-13/bin/clang++
#LD = /home/justin/.local/lib/jsix/toolchains/llvm-13/bin/ld.lld
#CC = g++
#LD = ld
#CC = clang++-13
#LD = clang++-13
#LD = ld.lld-13
CC = clang++-16
LD = ld.lld-16

got: foo.o bar.o
	${LD} -pie -o $@ $^

%.o: %.cpp
	${CC} -c -g -fpie -o $@ $^

dump: got
	${CC} --version
	objdump -M intel -DS -j .text $^

clean:
	-rm *.o got

.PHONY: rip clean

output

g++ -c -g -fpie -o foo.o foo.cpp
g++ -c -g -fpie -o bar.o bar.cpp
ld -pie -o got foo.o bar.o
g++ --version
g++ (Debian 12.3.0-5) 12.3.0
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

objdump -M intel -DS -j .text got

got:     file format elf64-x86-64


Disassembly of section .text:

0000000000001000 <main>:
extern unsigned long _GLOBAL_OFFSET_TABLE_ [];
extern unsigned long SOME_GLOBAL;

int main() {
    1000:	55                   	push   rbp
    1001:	48 89 e5             	mov    rbp,rsp
    auto foo1 = &_GLOBAL_OFFSET_TABLE_;
    1004:	48 8d 05 dd 2f 00 00 	lea    rax,[rip+0x2fdd]        # 3fe8 <_GLOBAL_OFFSET_TABLE_>
    100b:	48 89 45 f8          	mov    QWORD PTR [rbp-0x8],rax
    auto foo2 =  _GLOBAL_OFFSET_TABLE_;
    100f:	48 8d 05 d2 2f 00 00 	lea    rax,[rip+0x2fd2]        # 3fe8 <_GLOBAL_OFFSET_TABLE_>
    1016:	48 89 45 f0          	mov    QWORD PTR [rbp-0x10],rax

    auto bar1 = &SOME_GLOBAL;
    101a:	48 8d 05 df 2f 00 00 	lea    rax,[rip+0x2fdf]        # 4000 <SOME_GLOBAL>
    1021:	48 89 45 e8          	mov    QWORD PTR [rbp-0x18],rax
    auto bar2 =  SOME_GLOBAL;
    1025:	48 8b 05 d4 2f 00 00 	mov    rax,QWORD PTR [rip+0x2fd4]        # 4000 <SOME_GLOBAL>
    102c:	48 89 45 e0          	mov    QWORD PTR [rbp-0x20],rax

    return 0;
    1030:	b8 00 00 00 00       	mov    eax,0x0
}
    1035:	5d                   	pop    rbp
    1036:	c3                   	ret



clang++-16 -c -g -fpie -o foo.o foo.cpp
clang++-16 -c -g -fpie -o bar.o bar.cpp
ld.lld-16 -pie -o got foo.o bar.o
clang++-16 --version
Debian clang version 16.0.6 (6)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
objdump -M intel -DS -j .text got

got:     file format elf64-x86-64


Disassembly of section .text:

0000000000001290 <main>:
extern unsigned long _GLOBAL_OFFSET_TABLE_ [];
extern unsigned long SOME_GLOBAL;

int main() {
    1290:	55                   	push   rbp
    1291:	48 89 e5             	mov    rbp,rsp
    1294:	c7 45 fc 00 00 00 00 	mov    DWORD PTR [rbp-0x4],0x0
    auto foo1 = &_GLOBAL_OFFSET_TABLE_;
    129b:	48 8b 05 c6 20 00 00 	mov    rax,QWORD PTR [rip+0x20c6]        # 3368 <_GLOBAL_OFFSET_TABLE_>
    12a2:	48 89 45 f0          	mov    QWORD PTR [rbp-0x10],rax
    auto foo2 =  _GLOBAL_OFFSET_TABLE_;
    12a6:	48 8b 05 bb 20 00 00 	mov    rax,QWORD PTR [rip+0x20bb]        # 3368 <_GLOBAL_OFFSET_TABLE_>
    12ad:	48 89 45 e8          	mov    QWORD PTR [rbp-0x18],rax

    auto bar1 = &SOME_GLOBAL;
    12b1:	48 8d 05 a8 20 00 00 	lea    rax,[rip+0x20a8]        # 3360 <SOME_GLOBAL>
    12b8:	48 89 45 e0          	mov    QWORD PTR [rbp-0x20],rax
    auto bar2 =  SOME_GLOBAL;
    12bc:	48 8d 05 9d 20 00 00 	lea    rax,[rip+0x209d]        # 3360 <SOME_GLOBAL>
    12c3:	48 8b 00             	mov    rax,QWORD PTR [rax]
    12c6:	48 89 45 d8          	mov    QWORD PTR [rbp-0x28],rax

    return 0;
    12ca:	31 c0                	xor    eax,eax
    12cc:	5d                   	pop    rbp
    12cd:	c3                   	ret
    12ce:	cc                   	int3
    12cf:	cc                   	int3