Bug 250024 - cannot set CPU register value
cannot set CPU register value
Status: CLOSED CURRENTRELEASE
Product: Fedora
Classification: Fedora
Component: gdb (Show other bugs)
9
i386 Linux
low Severity medium
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Assigned To: Jan Kratochvil
Fedora Extras Quality Assurance
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Depends On:
Blocks:
  Show dependency treegraph
 
Reported: 2007-07-29 14:13 EDT by John Reiser
Modified: 2008-08-11 13:52 EDT (History)
2 users (show)

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Environment:
Last Closed: 2008-08-11 13:52:10 EDT
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Regression: ---
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Documentation: ---
CRM:
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---


Attachments (Terms of Use)
Fix - port of the amd64 frameless handling for i386. (1.08 KB, patch)
2007-07-29 19:10 EDT, Jan Kratochvil
no flags Details | Diff

  None (edit)
Description John Reiser 2007-07-29 14:13:56 EDT
Description of problem: gdb cannot set the contents of a CPU register:
  (gdb) set $eax=3
  Value being assigned to is no longer active.
  (gdb) p $eax
  $1 = 0x0


Version-Release number of selected component (if applicable):
GNU gdb Red Hat Linux (6.6-15.fc7rh)

How reproducible: always


Steps to Reproduce:
1. Try to change register value, for instance with "set $eax = 3"
2.
3.
  
Actual results:
"Value being assigned to is no longer active." and the register value does not
change.

Expected results: The contents of the register changes to the new value.


Additional info:
Here is a short test program:
----- ps.S
#include <asm/unistd.h>

_start: .globl _start
        sub %ebx,%ebx
        int3
        jnz good
        incl %ebx
good:
        movl $__NR_exit,%eax
        int $0x80
-----

$ gcc -o ps -nostartfiles -nostdlib ps.S
$ gdb ps
(gdb) run

Program received signal SIGTRAP, Trace/breakpoint trap.
0x08048057 in _start ()
(gdb) set $eax = 3
Value being assigned to is no longer active.
(gdb)
Comment 1 Jan Kratochvil 2007-07-29 19:10:05 EDT
Created attachment 160208 [details]
Fix - port of the amd64 frameless handling for i386.

It affects only artifical code / functions with broken stack frames.
For a normal C code you can set the registers even on i386.
Testing RPM is now being built at:
  http://koji.fedoraproject.org/koji/taskinfo?taskID=81273
Thanks for the report, regressions check / integration / upstream post to be
done.
Comment 2 John Reiser 2007-07-29 22:02:21 EDT
gdb-6.6-23.fc7.i386.rpm works for me.  Thank you.
Comment 3 Jan Kratochvil 2007-07-30 04:42:16 EDT
Posted upstream:
http://sources.redhat.com/ml/gdb-patches/2007-07/msg00307.html
Comment 4 Jan Kratochvil 2007-07-30 08:04:43 EDT
Comment on attachment 160208 [details]
Fix - port of the amd64 frameless handling for i386.

My patch is wrong, though.
More info in the upstream mailing list.
Comment 5 Bug Zapper 2008-05-14 09:44:40 EDT
This message is a reminder that Fedora 7 is nearing the end of life. Approximately 30 (thirty) days from now Fedora will stop maintaining and issuing updates for Fedora 7. It is Fedora's policy to close all bug reports from releases that are no longer maintained. At that time this bug will be closed as WONTFIX if it remains open with a Fedora 'version' of '7'.

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Comment 6 John Reiser 2008-05-14 11:22:09 EDT
This problem persists in Fedora 9, gdb-6.8-5.fc9.i386.  I updated the header of
this bugzilla report to say Version 9.
Comment 7 Denys Vlasenko 2008-08-11 11:29:04 EDT
Works for me:

# gcc -o ps -nostartfiles -nostdlib ps.S
# gdb ps
GNU gdb Fedora (6.8-12.fc9)
Copyright (C) 2008 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-redhat-linux-gnu"...
(no debugging symbols found)
(gdb) run
Starting program: /tmp/ps
(no debugging symbols found)

Program received signal SIGTRAP, Trace/breakpoint trap.
0x00000000004000d7 in _start ()
(gdb) set $eax = 3
(gdb) quit
The program is running.  Exit anyway? (y or n) y



Version, arch:

# gdb --version
GNU gdb Fedora (6.8-12.fc9)
Copyright (C) 2008 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-redhat-linux-gnu".
Comment 8 John Reiser 2008-08-11 13:52:10 EDT
gdb-6.8-17.fc9 also works for me.  So -17 and -12 work, but -5 still had the problem.  I hope it continues to work.  I changed Status to Closed - Current Release.

This looks to be strongly related to bug #436037, "gdb remote fails qemu: Value being assigned to is no longer active".  One theme seems to be keeping hardware registers fully active regardless of the status of other pieces of the environment, such as symbol tables, stack traces, etc.

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