How to access variable in main function in c using x86 assembly - c++

Question

This is my main function
#include<stdio.h>
#include<stdlib.h>
int name1(int g);
char* getStringFromC(void);
int main(){
int a=2;
char* g="this is called from assembly";
printf("%d\n",name1(a));
return 0;
}
.text
.globl name1
name1:
push %ebp
movl %esp, %ebp
movl 8(%ebp),%eax
movl %ebp,%esp
popl %ebp
ret//This function name1(int a) in assembly
Problem is how to access char* g from assembly ?? I though was 12(%ebp) or 16(%ebp) should contain that values which are like char* g and so on..

Answer 1

You're not supposed to. If it wasn't included as parameter and is not global, you shouldn't try to access it.
But for the sake of completeness, I'll answer anyway: Use the frame pointer. %ebp points to its previous value. Copy it to a scratch register and you can index the caller's local variables through it.

Answer 2

The example below does what you seem to want, and also shows how to
access a global variable. This works on my Ubuntu 13.10 x64 system.
As noted by Medinoc and hvd, looking at the stack in the way you're
trying to do isn't robust.
Makefile:
CFLAGS=-Wall -Wextra
all: main
main: main.o lib.o
main.c:
#include <stdio.h>
void* stack_peek(int g);
void* get_global_str(void);
char const *global_str="Global";
int main(){
int a=2;
char const * g="this is called from assembly";
printf("stack_peek(a): %p\n",stack_peek(a));
printf("g: %p\n",(void*)g);
printf("global_str: %p\n",(void*)global_str);
printf("get_global_str(): %p\n",(void*)get_global_str());
return 0;
}
lib.s:
.text
.globl global_str
.type global_str, #common
.globl stack_peek
.type stack_peek, #function
stack_peek:
pushq %rbp
movq %rsp, %rbp
movq 24(%rbp),%rax
movq %rbp,%rsp
popq %rbp
ret
.globl get_global_str
.type get_global_str, #function
get_global_str:
movq global_str,%rax
ret
Output:
$ make -B
cc -Wall -Wextra -c -o main.o main.c
as -o lib.o lib.s
cc main.o lib.o -o main
$ ./main
stack_peek(a): 0x40067b
g: 0x40067b
global_str: 0x400674
get_global_str(): 0x400674