What do gcc assembly output labels mean?

Question

I wrote a simple C program test.c:

#include <stdio.h>
#include <stdlib.h>
int add(int a, int b);
int main()
{
    int i=5,j=10;
    int result;
    result = add(i, j);
    printf("result is %d\n", result);
}
int add(int a, int b)
{
    return (a + b);
}

and I compiled it:

gcc -S -Os -o test.s test.c 

and I get the build file test.s:

        .file   "test3.c"
    .section    .rodata
.LC0:
    .string "result is %d\n"
    .text
.globl main
    .type   main, @function
main:
.LFB5:
    pushq   %rbp
.LCFI0:
    movq    %rsp, %rbp
.LCFI1:
    subq    $16, %rsp
.LCFI2:
    movl    $5, -12(%rbp)
    movl    $10, -8(%rbp)
    movl    -8(%rbp), %esi
    movl    -12(%rbp), %edi
    call    add
    movl    %eax, -4(%rbp)
    movl    -4(%rbp), %esi
    movl    $.LC0, %edi
    movl    $0, %eax
    call    printf
    leave
    ret
.LFE5:
    .size   main, .-main
.globl add
    .type   add, @function
add:
.LFB6:
    pushq   %rbp
.LCFI3:
    movq    %rsp, %rbp
.LCFI4:
    movl    %edi, -4(%rbp)
    movl    %esi, -8(%rbp)
    movl    -8(%rbp), %eax
    addl    -4(%rbp), %eax
    leave
    ret
.LFE6:
    .size   add, .-add
    .section    .eh_frame,"a",@progbits
.Lframe1:
    .long   .LECIE1-.LSCIE1
.LSCIE1:
    .long   0x0
    .byte   0x1
    .string "zR"
    .uleb128 0x1
    .sleb128 -8
    .byte   0x10
    .uleb128 0x1
    .byte   0x3
    .byte   0xc
    .uleb128 0x7
    .uleb128 0x8
    .byte   0x90
    .uleb128 0x1
    .align 8
.LECIE1:
.LSFDE1:
    .long   .LEFDE1-.LASFDE1
.LASFDE1:
    .long   .LASFDE1-.Lframe1
    .long   .LFB5
    .long   .LFE5-.LFB5
    .uleb128 0x0
    .byte   0x4
    .long   .LCFI0-.LFB5
    .byte   0xe
    .uleb128 0x10
    .byte   0x86
    .uleb128 0x2
    .byte   0x4
    .long   .LCFI1-.LCFI0
    .byte   0xd
    .uleb128 0x6
    .align 8
.LEFDE1:
.LSFDE3:
    .long   .LEFDE3-.LASFDE3
.LASFDE3:
    .long   .LASFDE3-.Lframe1
    .long   .LFB6
    .long   .LFE6-.LFB6
    .uleb128 0x0
    .byte   0x4
    .long   .LCFI3-.LFB6
    .byte   0xe
    .uleb128 0x10
    .byte   0x86
    .uleb128 0x2
    .byte   0x4
    .long   .LCFI4-.LCFI3
    .byte   0xd
    .uleb128 0x6
    .align 8
.LEFDE3:
    .ident  "GCC: (GNU) 4.1.2 20080704 (Red Hat 4.1.2-48)"
    .section    .note.GNU-stack,"",@progbits

I understand all of these instructions, but I really don't understand what these labels mean. .LC0, .LFB5, .LCFI0, .LCFI1, .LCFI2, .LFE5, ... These tags are automatically generated gcc. Why are these shortcuts needed? Some tags seem to be redundant.

• gcc version: 4.1.2
• machine: x86_64

Answer 1

The compiler will generate a label for any place where it should refer to the address, whether for a jump or jump instruction, or for a data location.

, , , , , .

( ) , . .

, LCx LFBx, . , , , .

---

, , , module /trunk/gcc/dwarf2out.c, , , , . 250 , . , 23 000 , .

Answer 2

gcc -fverbose-asm -fdump-tree-all -S -Os -o test.s test.c , " " test.c.*, GCC.

. , GCC .

, GCC (Gimple, Tree). ( ) . , Gimple ..

http://gcc-melt.org/ ( ).

MELT (, , GCC 4.6 ) ( ) GCC, MELT .

---

:

gcc-4.1 . GCC 4.7 ( 4.7.0 second release). GCC 4,1 ( 2006 ). ( 4.6), . GCC [e-mail] ( , ), GCC 4.1. [e-mail] GCC (.. ).