where is the string literal allocated ? On the stack ?

[Michael]

----- Original Message ----- 
From: "Brian Dessent" <brian@dessent.net>
To: "Michael Gong" <mwgong@cs.toronto.edu>
Cc: <gcc-help@gcc.gnu.org>
Sent: Friday, April 20, 2007 12:28 PM
Subject: Re: where is the string literal allocated ? On the stack ?


> Michael Gong wrote:
>
>> Though it's not related with gcc, could anyone help me with following
>> question:
>>
>> Where is the string literal allocated ? Is it on the stack ?
>>
>> For example, where is "abc" allocated ?
>>
>> char * foo() {
>>     return "abc";
>> }
>
> Everyone else has already answered your question directly, but I'd 
> like
> to point out that the compiler is not a black box -- you can easily 
> see
> exactly what it's doing with a few simple commands.  Check the docs 
> for
> on -S, -save-temps, -fverbose-asm, etc.  For example:
>
> $ echo 'char * foo() { return "abc"; }' | gcc -x c - -S -o
> -
>        .file   ""
>        .section        .rodata
> .LC0:
>        .string "abc"
>        .text
> .globl foo
>        .type   foo, @function
> foo:
>        pushl   %ebp
>        movl    %esp, %ebp
>        movl    $.LC0, %eax
>        popl    %ebp
>        ret
>        .size   foo, .-foo
>        .ident  "GCC: (GNU) 4.0.4 20060507 (prerelease) (Debian
> 4.0.3-3)"
>        .section        .note.GNU-stack,"",@progbits
>
> As you can see, it goes in the .rodata section.  The above is the
> behavior under linux, but for PE (Win32) it is a different section:
>
> $ echo 'char * foo() { return "abc"; }' | gcc -x c - -S -o -
>        .file   ""
>        .section .rdata,"dr"
> LC0:
>        .ascii "abc\0"
>        .text
> .globl _foo
>        .def    _foo;   .scl    2;      .type   32;     .endef
> _foo:
>        pushl   %ebp
>        movl    %esp, %ebp
>        movl    $LC0, %eax
>        popl    %ebp
>        ret
>
> That is my second point: this kind of thing is platform-dependant
> (although it can never be on the stack), and you didn't mention at all
> what platform you are using in your original question, which should be 
> a
> requirement for almost any compiler/toolchain question.
>
> Brian
>

Thanks for the comments.

Actually, I don't care about the exact location :-)  All I need to know 
is whether it is on the stack. Therefore, I don't mention the platform 
in the question.

Mike