Re: [patch+7.5.1] Work around PR libc/13097 "linux-vdso.so.1" #3

["H.J. Lu" <hjl.tools@gmail.com>]

On Thu, Nov 22, 2012 at 12:17 PM, Jan Kratochvil
<jan.kratochvil@redhat.com> wrote:
> Hi,
>
> this is an updated version of
>         [RFC] Work around PR libc/13097 "linux-vdso.so.1" #2
>         http://sourceware.org/ml/gdb-patches/2011-08/msg00331.html
> according to the Tom's comment
>         http://sourceware.org/bugzilla/show_bug.cgi?id=14466#c3
>
> I remembered it when Joel plans 7.5.1 release, the patch is safe enough and it
> is a FAQ at least on IRC.
>
> Fedora does not have this issue with its Fedora glibc but I have it
> reproducible with FSF glibc build:
>         ./gdb -ex r --args $HOME/glibc-root/lib/ld-linux-x86-64.so.2 --library-path $HOME/glibc-root/lib /bin/true
>         Starting program: /home/.../glibc-root/lib/ld-linux-x86-64.so.2 --library-path /home/.../glibc-root/lib /bin/true
>         warning: Could not load shared library symbols for linux-vdso.so.1.
>         Do you need "set solib-search-path" or "set sysroot"?
>         [Inferior 1 (process 31807) exited normally]
>
> So there is no testcase as I do not know a real OS where it fails (it probably
> fails on Ubuntu AFAIK).
>
> No regressions on {x86_64,x86_64-m32,i686}-fedora18-linux-gnu.
>
>

vdso is available from /proc:

#include <stdio.h>
#include <string.h>

int
main()
{
	FILE *maps;
	void *vdso_begin, *vdso_end;

	maps = fopen("/proc/self/maps", "r");
	char buf[1024];
	while (fgets(buf, 1024, maps)) {
		if (strstr(buf, "[vdso]")) break;
	}
	fclose(maps);

	sscanf(buf, "%p-%p", &vdso_begin, &vdso_end);
	write(1, vdso_begin, vdso_end - vdso_begin);

	return 0;
}

or

extern int dl_iterate_phdr (int (*__callback) (struct dl_phdr_info *,
                                               size_t, void *),
                            void *__data);

Can GDB use them to locate vdso?