Finding the source code for ___tls_get_addr_internal()

[Ian Lance Taylor]

On Wed, Jan 16, 2013 at 3:17 PM, Saul Tamari <stamari@gmail.com> wrote:
>
> I'm using a GNU/Linux on an Intel 32bit x86.
>
> I think that I might be digging too deep. There shouldn't be any
> problem with the gs segment or whatever it points to.
>
> The application is a C program that dynamically loads (using dlopen())
> C++ libraries.
> Do I need to set -ftls-model=global-dynamic when compiling the various
> C++ libraries so TLS works correctly?

Normally that will happen automatically when you use -fPIC.  Since you
are using 32-bit x86, I guess it is possible that you are compiling
code without -fPIC and then putting it in a shared library and then
using dlopen.  If so, that is your problem; use -fPIC.

If you are using -fPIC, then I do not know what is wrong.

> Now in order to get eax's value before the call to ___tls_get_attr() I do:
> 0xf6f536d9 + 0x3591b = 0xf6f88ff4
> 0xf6f88ff4 - 0x56c = 0xf6f88a88
>
> Can this value help me locate which tls value is accessed here? Can I
> find it with readelf or objdump?

I don't know of any easy way to from that address to the variable
being accessed.

By looking at the source code for __cxa_get_globals (which is part of
GCC, not glibc) I can tell you that the variable in question is a
static __thread variable defined in
libstdc++-v3/libsupc++/eh_globals.cc.  The variabls is used to keep
track of all the C++ exceptions currently being thrown.

Ian