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Date: Mon, 03 Dec 2007 17:48:00 -0000
From: "Manuel Arriaga" <manuelarriaga1980@gmail.com>
To: binutils@sourceware.org
Subject: identifying symbol versions available to dlvsym
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Hello everyone,

I am trying to determine which versions of a given symbol (in this
case, fopen) are available in a system's GNU libc for loading through
dlvsym().  How can I do that?

I thought I could get this from objdump


$ objdump -T /lib/libc-2.6.1.so |grep " fopen$"
000575f0 g    DF .text  00000032  GLIBC_2.1   fopen
000f9380 g    DF .text  00000097 (GLIBC_2.0)  fopen


but then I tried running the attached program on the two versions
listed for fopen (GLIBC_2.0 and GLIBC_2.1) and it failed

$ ./dlvsym fopen GLIBC_2.1
fp= 0
dlerror()==NULL
$ ./dlvsym fopen GLIBC_2.0
fp= 0
dlerror()==NULL

Through "brute-force"ing version numbers, I identified the version
GLIBC_2.2.5 as available on this system:

$ ./dlvsym fopen GLIBC_2.2.5
fp= 1772397760
dlerror()==NULL

But then I have another system with an earlier GNU libc version
(2.3.5) in which objdump lists the same symbol versions yet I can only
load fopen version GLIBC_2.1 using dlvsym.

What is the correct way to identify which versions of a given function
I can load with dlvsym?

Thank you for any help

Manuel