[Bug corefiles/11608] gcore does not support build-id

["jan.kratochvil at redhat dot com" <sourceware-bugzilla@sourceware.org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=11608

Jan Kratochvil <jan.kratochvil at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jan.kratochvil at redhat
                   |                            |dot com
            Version|unknown                     |7.5

--- Comment #1 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2012-08-09 08:41:34 UTC ---
In practice it works now although it depends on something accidentally
happening in Linux kernel:

echo 'const int i[2000]={0};void _start(void){}'|gcc -Wall -nostdlib
-fno-asynchronous-unwind-tables -Wl,--build-id -x c -;gdb -nx ./a.out -ex 'b
*_start' -ex r -ex 'gcore core' -ex 'set confirm no' -ex q;eu-unstrip -n
--core=core
[...]
0x400000+0x400000 2fb48d92cfa19eb24524f14211565853e3da3deb@0x400284 - - [exe]

It works since:
http://sourceware.org/ml/gdb-patches/2012-08/msg00225.html

But it is more accidental:
$ cat /proc/22440/smaps
00400000-00401000 r-xp 00000000 fd:02 15079087 /home/jkratoch/t/a.out
Shared_Dirty:          0 kB
Private_Dirty:         4 kB
Anonymous:             4 kB
Swap:                  0 kB

Despite it is r-x Linux kernel had to write there some data - see Private_Dirty
and Anonymous.  I do not know why, Linux kernel hackers could advice.

gcc (GCC) 4.7.2 20120809 (prerelease)
GNU gdb (GDB) 7.5.50.20120809-cvs
binutils-2.22.52.0.4-8.fc18.x86_64
kernel-3.4.6-1.fc16.x86_64

The right fix would be to see the '[exe]' line even with gdb-7.5 or earlier
(not FSF GDB HEAD where is committed the patch for PR 11804 above).  Earlier
GDBs did not pay attention to the 4 lines in smaps and thus they did not dump
the build-id page so that the '[exe]' line was not visible.

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