What is -fverbose-asm trying to say in assembly?

问题

I have compiled this function:

void print_ints(int len, ...){
    va_list args;
    va_start(args, len);

    for(int i =0; i<len ; i++)
    {
        int val = va_arg(args,int);
        printf("i:%i\tval:%i\n",i,val);
    }

    va_end(args);
}

into this assembly:

print_ints:
pushq   %rbp    #
    movq    %rsp, %rbp  #,
    subq    $224, %rsp  #,
    movl    %edi, -212(%rbp)    # len, len
    movq    %rsi, -168(%rbp)    #,
    movq    %rdx, -160(%rbp)    #,
    movq    %rcx, -152(%rbp)    #,
    movq    %r8, -144(%rbp) #,
    movq    %r9, -136(%rbp) #,
    testb   %al, %al    #
    je  .L7 #,
    movaps  %xmm0, -128(%rbp)   #,
    ...
.L7:
# a.c:7:    va_start(args, len);
    movl    $8, -208(%rbp)  #, MEM[(struct [1] *)&args].gp_offset
    movl    $48, -204(%rbp) #, MEM[(struct [1] *)&args].fp_offset
    leaq    16(%rbp), %rax  #, tmp100
    movq    %rax, -200(%rbp)    # tmp100, MEM[(struct [1] *)&args].overflow_arg_area
    leaq    -176(%rbp), %rax    #, tmp101
    movq    %rax, -192(%rbp)    # tmp101, MEM[(struct [1] *)&args].reg_save_area
# a.c:9:    for(int i =0; i<len ; i++)
    movl    $0, -180(%rbp)  #, i
# a.c:9:    for(int i =0; i<len ; i++)
    jmp .L3 #
.L6:
# a.c:11:       int val = va_arg(args,int);
    movl    -208(%rbp), %eax    # MEM[(struct  *)&args].gp_offset, D.2882
    cmpl    $47, %eax   #, D.2882
    ja  .L4 #,
# a.c:11:       int val = va_arg(args,int);
    ...

I know it looks like mess, but there are some part of the output I am interested in. Specially lines like this:

movl    $8, -208(%rbp)  #, MEM[(struct [1] *)&args].gp_offset

I would try to analyse it:

MEM[...] -> could represent a whole memory as an array (an addresses as a index)
MEM[(struct[1]*)...] -> could represent a type, which this type itself is a member of some unknown struct struct[1]* gives then pointer to a type of the second member of that struct
MEM[(struct[1]*)&args] -> once the data type (length) is specified (struct[1]*), it reside at address of variable args, so know we know, where to start
MEM[(struct[1]*)&args].gp_offset -> So we have a type, a start address which together gives us a index to global memory table, which obtain a "some value" upon which we want to access to get gp_offset ?

Is my surmises correct? What members or functions (or what it is) are the members gained ->

gp_offset, fp_offset, overflow_arg_area, reg_save_area, ...

Can I find an implementation of them to see what they does? or are they documented under compiler internals?

来源：https://stackoverflow.com/questions/62478718/what-is-fverbose-asm-trying-to-say-in-assembly

标签

assembly

gcc

x86-64

variadic-functions