Re: thread local storage (__thread) variables aren't working in gdb 6.5/6.6?

["John Bates" <johnnybates at gmail dot com>]

It would be helpful to update the GDB man/info/docs to state that
thread local storage is not supported. It would also help to print an
error when attempting to access TLS __thread variable that says
"thread local storage is not supported." Currently, GDB implies that
__thread variables are bad addresses--for example, "Cannot access
memory at address 0x0". I have verified the same result in GDB 6.4,
6.5 and 6.6, with and without libpthread linked with the ELF. A simple
test case is in the email below if anyone is interested in checking
this.

Best regards,
John


On 6/19/07, John Bates <johnnybates@gmail.com> wrote:
> I can't find any confirmation of support or non-support of thread
> local storage on the web or in the gdb documentation. I already tried
> 6.6 and it was the same problem. The test below seems to confirm
> non-support on my fedora core 6 (kernel 2.6.18) x86 distribution with
> gdb 6.5. Please let me know if I am doing something wrong for
> debugging __thread global variables.
>
> Thanks,
> John
>
>
> --- begin main.cpp ---
> __thread int tlstest = 5;
>
> int main()
> {
>         tlstest = 4; // line 5
>         return 0;
> }
>
> --- begin Makefile ---
> CXXFLAGS += -g
> main : main.o
>
> jbates@localhost:~/samples/tls_test$ make
> g++ -g   -c -o main.o main.cpp
> cc   main.o   -o main
> jbates@localhost:~/samples/tls_test$ gdb main
> GNU gdb Red Hat Linux (6.5-15.fc6rh)
> Copyright (C) 2006 Free Software Foundation, Inc.
> GDB is free software, covered by the GNU General Public License, and you are
> welcome to change it and/or distribute copies of it under certain conditions.
> Type "show copying" to see the conditions.
> There is absolutely no warranty for GDB.  Type "show warranty" for details.
> This GDB was configured as "i386-redhat-linux-gnu"...Using host
> libthread_db library "/lib/libthread_db.so.1".
>
> (gdb) b main.cpp:5
> Breakpoint 1 at 0x8048352: file main.cpp, line 5.
> (gdb) run
> Starting program: /home/jbates/samples/tls_test/main
>
> Breakpoint 1, main () at main.cpp:5
> 5               tlstest = 4;
> (gdb) p tlstest
> Cannot access memory at address 0x0
> (gdb)