本文介绍了运行外部编译器(godbolt)程序集的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
假设我有以下C程序:
int main() {
int a = 1;
int b = 2;
return a + b;
}
在编译器资源管理器为我提供了
main:
pushq %rbp
movq %rsp, %rbp
movl $1, -4(%rbp)
movl $2, -8(%rbp)
movl -4(%rbp), %edx
movl -8(%rbp), %eax
addl %edx, %eax
popq %rbp
ret
这(某种程度上)类似于通过gcc进行编译所产生的效果，至少对于main部分而言.但是，这不会编译为独立"文件，例如，如果我将asm复制粘贴到文件gb.s中并运行$ gcc gb.s，则会收到错误消息:
This is (somewhat) similar to what compiling via gcc gives me, at least for the main part. However, this will not compile as a "stand-alone", for example if I copy-paste the asm into a file gb.s and run $ gcc gb.s I get an error:
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 0 has invalid symbol index 11
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 1 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 2 has invalid symbol index 2
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 3 has invalid symbol...
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_line): relocation 0 has invalid symbol index 2
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status
-除非我也将.globl放在顶部，例如:
-- unless I also include the .globl at the top, for example:
.globl main
由此，我有两个问题:
- godbolt编译器为什么不在顶部包含它，或者使它自成一体?
- 有没有一种方法可以运行
gcc并告诉它main是主要/全局部分，而不必将.globl main放在顶部?
- Why doesn't the godbolt compiler contain that at the top, or something else to make it self-contained?
- Is there a way to run
gccand tell it thatmainis the main/global section without putting.globl mainat the top?
推荐答案
一个好男人 Matt Godbolt 付出了很多努力来过滤生成的所有噪声组装
A good man Matt Godbolt has put a lots of effort to filter all the noise form the generated assembly
.file "example.c"
.text
.Ltext0:
.globl main
.type main, @function
main:
.LFB0:
.file 1 "./example.c"
.loc 1 1 12
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
.loc 1 2 9
movl $1, -4(%rbp)
.loc 1 3 9
movl $2, -8(%rbp)
.loc 1 4 14
movl -4(%rbp), %edx
movl -8(%rbp), %eax
addl %edx, %eax
.loc 1 5 1
popq %rbp
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE0:
.size main, .-main
.Letext0:
.section .debug_info,"",@progbits
.Ldebug_info0:
.long 0x6e
.value 0x4
.long .Ldebug_abbrev0
.byte 0x8
.uleb128 0x1
.long .LASF0
.byte 0xc
.long .LASF1
.long .LASF2
.quad .Ltext0
.quad .Letext0-.Ltext0
.long .Ldebug_line0
.uleb128 0x2
.long .LASF3
.byte 0x1
.byte 0x1
.byte 0x5
.long 0x6a
.quad .LFB0
.quad .LFE0-.LFB0
.uleb128 0x1
.byte 0x9c
.long 0x6a
.uleb128 0x3
.string "a"
.byte 0x1
.byte 0x2
.byte 0x9
.long 0x6a
.uleb128 0x2
.byte 0x91
.sleb128 -20
.uleb128 0x3
.string "b"
.byte 0x1
.byte 0x3
.byte 0x9
.long 0x6a
.uleb128 0x2
.byte 0x91
.sleb128 -24
.byte 0
.uleb128 0x4
.byte 0x4
.byte 0x5
.string "int"
.byte 0
.section .debug_abbrev,"",@progbits
.Ldebug_abbrev0:
.uleb128 0x1
.uleb128 0x11
.byte 0x1
.uleb128 0x25
.uleb128 0xe
.uleb128 0x13
.uleb128 0xb
.uleb128 0x3
.uleb128 0xe
.uleb128 0x1b
.uleb128 0xe
.uleb128 0x11
.uleb128 0x1
.uleb128 0x12
.uleb128 0x7
.uleb128 0x10
.uleb128 0x17
.byte 0
.byte 0
.uleb128 0x2
.uleb128 0x2e
.byte 0x1
.uleb128 0x3f
.uleb128 0x19
.uleb128 0x3
.uleb128 0xe
.uleb128 0x3a
.uleb128 0xb
.uleb128 0x3b
.uleb128 0xb
.uleb128 0x39
.uleb128 0xb
.uleb128 0x49
.uleb128 0x13
.uleb128 0x11
.uleb128 0x1
.uleb128 0x12
.uleb128 0x7
.uleb128 0x40
.uleb128 0x18
.uleb128 0x2117
.uleb128 0x19
.uleb128 0x1
.uleb128 0x13
.byte 0
.byte 0
.uleb128 0x3
.uleb128 0x34
.byte 0
.uleb128 0x3
.uleb128 0x8
.uleb128 0x3a
.uleb128 0xb
.uleb128 0x3b
.uleb128 0xb
.uleb128 0x39
.uleb128 0xb
.uleb128 0x49
.uleb128 0x13
.uleb128 0x2
.uleb128 0x18
.byte 0
.byte 0
.uleb128 0x4
.uleb128 0x24
.byte 0
.uleb128 0xb
.uleb128 0xb
.uleb128 0x3e
.uleb128 0xb
.uleb128 0x3
.uleb128 0x8
.byte 0
.byte 0
.byte 0
.section .debug_aranges,"",@progbits
.long 0x2c
.value 0x2
.long .Ldebug_info0
.byte 0x8
.byte 0
.value 0
.value 0
.quad .Ltext0
.quad .Letext0-.Ltext0
.quad 0
.quad 0
.section .debug_line,"",@progbits
.Ldebug_line0:
.section .debug_str,"MS",@progbits,1
.LASF2:
.string "/home/ce"
.LASF3:
.string "main"
.LASF0:
.string "GNU C17 9.3.0 -mtune=generic -march=x86-64 -g"
.LASF1:
.string "./example.c"
.ident "GCC: (Compiler-Explorer-Build) 9.3.0"
.section .note.GNU-stack,"",@progbits
简单地取消选中指令"
Simple untick the "Directives"
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