From: Jie Zhang <jie.zhang@analog.com>
To: yunfeng zhang <zyf.zeroos@gmail.com>
Cc: Richard Henderson <rth@redhat.com>,
gcc@gcc.gnu.org, Andrew Haley <aph@redhat.com>
Subject: Re: No .got section in ELF
Date: Fri, 27 Nov 2009 04:58:00 -0000 [thread overview]
Message-ID: <4B0F5C70.7010102@analog.com> (raw)
In-Reply-To: <4df04b840911252204g33297e18m8e189c62a0662378@mail.gmail.com>
On 11/26/2009 02:04 PM, yunfeng zhang wrote:
> The result is the same
>
> #include<stdio.h>
>
> extern int g __attribute__((visibility("hidden")));
> int g;
>
> int foo(int a, int b)
> {
> g = a + b;
> printf("%x, %x",&g, foo);
> return g;
> }
>
> load and call `foo' in the library, an outputting (with vdso) is
> cc15bc, cc03fc
> and open f.map
> 0x15bc, 0x3fc
>
> It shows Linux simply maps the library to memory *using* library segment layout.
>
> Using e.cc to call it
>
> #include<exception>
> #include<typeinfo>
> #include<cstddef>
> #include<dlfcn.h>
> #include<stdio.h>
>
> int main(void)
> {
> void* handle = dlopen("./f.so", RTLD_NOW);
> typedef int (*gso)(int, int);
> gso f;
> *(void**) (&f) = dlsym(handle, "foo");
> f(1, 2);
> return 0;
> }
>
You got the bad test case. Please try the following:
$ cat f.c
#include <stdio.h>
int g;
int foo(int a, int b)
{
g = a + b;
printf("&g = 0x%x, foo = 0x%x\n", &g, foo);
return g;
}
$ cat e.c
int g;
extern int foo(int a, int b);
int main(void)
{
foo(1, 2);
return 0;
}
$ gcc -shared -fPIC -Wl,-soname,./libf.so,-Map,f.map -o libf.so f.c
$ gcc -o e e.c -ldl -L. -lf
$ ./e
&g = 0x600a30, foo = 0x294a2614
Then comment out the "int g;" in e.c. and do the same steps as above:
$ ./e
&g = 0x58294948, foo = 0x58094614
You can see that "C-A" is *not* a constant. Your premise is wrong.
Jie
next prev parent reply other threads:[~2009-11-27 4:58 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-11-24 1:58 yunfeng zhang
2009-11-24 10:00 ` Andrew Haley
2009-11-24 17:10 ` Richard Henderson
2009-11-26 2:24 ` yunfeng zhang
2009-11-26 3:11 ` Richard Henderson
2009-11-26 6:04 ` yunfeng zhang
2009-11-26 7:55 ` Alexandre Oliva
2009-11-27 2:18 ` yunfeng zhang
2009-11-27 4:12 ` Dave Korn
2009-11-27 4:43 ` yunfeng zhang
2009-11-27 4:46 ` Dave Korn
2009-11-27 13:35 ` Alexandre Oliva
2009-11-30 11:10 ` Yunfeng ZHANG
2009-11-27 4:58 ` Jie Zhang [this message]
2009-11-27 6:42 ` yunfeng zhang
2009-11-27 14:16 ` Ian Lance Taylor
2009-11-27 4:51 Dmitry Gorbachev
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