Package: gdb
Version: 12.1-4
Severity: minor
X-Debbugs-Cc: msl0000023...@gmail.com
Hello.
The issue happens when I specific a return value to the 'return' command in
gdb(1), in order to return from a shared library function with my specified
return value.
The following example uses function geteuid(2) from libc.so.6:
root@debian:~/src# cat rval-test.c
#include <unistd.h>
#include <stdio.h>
int main() {
while(1) {
printf("geteuid returned %u\n", (unsigned
int)geteuid());
sleep(1);
}
}
root@debian:~/src# gcc -Wall -g rval-test.c -o rval-test
root@debian:~/src# gdb rval-test
GNU gdb (Debian 12.1-4) 12.1
Copyright (C) 2022 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 "powerpc64le-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from rval-test...
(gdb) b geteuid
Breakpoint 1 at 0x960
(gdb) r
Starting program: /root/src/rval-test
[Thread debugging using libthread_db enabled]
Using host libthread_db library
"/lib/powerpc64le-linux-gnu/libthread_db.so.1".
Breakpoint 1, 0x00007ffff7e12ea0 in __GI_geteuid () at
../sysdeps/unix/syscall-template.S:91
91 ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) c
Continuing.
geteuid returned 0
Breakpoint 1, 0x00007ffff7e12ea0 in __GI_geteuid () at
../sysdeps/unix/syscall-template.S:91
91 in ../sysdeps/unix/syscall-template.S
(gdb) return 111111
Make __GI_geteuid return now? (y or n) y
#0 0x00000001000008dc in main () at rval-test.c:6
6 printf("geteuid returned %u\n", (unsigned
int)geteuid());
(gdb) c
Continuing.
geteuid returned 0
Breakpoint 1, 0x00007ffff7e12ea0 in __GI_geteuid () at
../sysdeps/unix/syscall-template.S:91
91 ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) return (uint32_t)111111
Make __GI_geteuid return now? (y or n) y
#0 0x00000001000008dc in main () at rval-test.c:6
6 printf("geteuid returned %u\n", (unsigned
int)geteuid());
(gdb) c
Continuing.
geteuid returned 0
As shown in this example, I'm trying to make this function to return 111111
instead, but this didn't work.
Manually changing the register for return value (r3) worked:
Breakpoint 1, 0x00007ffff7e12ea0 in __GI_geteuid () at
../sysdeps/unix/syscall-template.S:91
91 ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) p $r3
$1 = 0
(gdb) p $r3 = (uint32_t)111111
$2 = 111111
(gdb) return
Make __GI_geteuid return now? (y or n) y
#0 0x00000001000008dc in main () at rval-test.c:6
6 printf("geteuid returned %u\n", (unsigned
int)geteuid());
(gdb) c
Continuing.
geteuid returned 111111
...
So this method could be used as a workaround.
-- System Information:
Debian Release: bookworm/sid
APT prefers unstable
APT policy: (500, 'unstable')
Architecture: ppc64el (ppc64le)
Kernel: Linux 5.4.0-113-generic (SMP w/128 CPU threads)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE,
TAINT_UNSIGNED_MODULE
Locale: LANG=C, LC_CTYPE=C.UTF-8 (charmap=UTF-8),
LANGUAGE=zh_TW:zh_CN:en_GB:en_US
Shell: /bin/sh linked to /usr/bin/dash
Init: unable to detect
Versions of packages gdb depends on:
ii libbabeltrace1 1.5.8-2+b2
ii libc6 2.35-3
ii libdebuginfod1 0.187-1
ii libexpat1 2.4.8-1
ii libgcc-s1 12.1.0-7
ii libgmp10 2:6.2.1+dfsg1-1
ii liblzma5 5.2.5-2.1
ii libmpfr6 4.1.0-3
ii libncursesw6 6.3+20220423-2
ii libpython3.10 3.10.5-1
ii libreadline8 8.1.2-1.2
ii libsource-highlight4v5 3.1.9-4.1+b1
ii libstdc++6 12.1.0-7
ii libtinfo6 6.3+20220423-2
ii libxxhash0 0.8.1-1
ii zlib1g 1:1.2.11.dfsg-4
Versions of packages gdb recommends:
ii libc6-dbg [libc-dbg] 2.35-3
Versions of packages gdb suggests:
pn gdb-doc <none>
pn gdbserver <none>
-- no debconf information
