[Bug threads/16413] New: Single-stepping function accessing TLS causes SIGSEGV of traced process

["gr.sourceware at anguta dot net" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=16413

            Bug ID: 16413
           Summary: Single-stepping function accessing TLS causes SIGSEGV
                    of traced process
           Product: gdb
           Version: 7.6
            Status: NEW
          Severity: normal
          Priority: P2
         Component: threads
          Assignee: unassigned at sourceware dot org
          Reporter: gr.sourceware at anguta dot net
            Target: x86_64-linux-gnu
             Build: Ubuntu 13.10

Created attachment 7341
  --> https://sourceware.org/bugzilla/attachment.cgi?id=7341&action=edit
Code snippet exhibiting the issue.

Hello,

I've been experiencing this bug for some time with various gdb versions up to
7.6.1 (included): When single-stepping a function accessing a TLS variable in a
PIC binary, the traced process gets a SIGSEGV.

I could reproduce this using a small code snippet, as attached.

Sample session below:

$ gcc -pthread -fPIC -g gdb-tls.c -o gdb-tls -lpthread
$ gdb ./gdb-tls 
GNU gdb (GDB) 7.6.1-ubuntu
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /tmp/gdb-tls...done.
(gdb) br foo
Breakpoint 1 at 0x4006a3: file gdb-tls.c, line 18.
(gdb) r
Starting program: /tmp/./gdb-tls 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Breakpoint 1, foo () at gdb-tls.c:18
18              global_tls++;
(gdb) n

Program received signal SIGSEGV, Segmentation fault.
foo () at gdb-tls.c:18
18              global_tls++;
(gdb)

Running this without gdb, or without breakpoints works fine.
Compiling without -fPIC fixes the issue, as well as with clang instead of gcc.

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