Date: Fri, 25 Aug 2000 00:42:31 -0400 From: John DeBoskey <jwd@unx.sas.com> To: freebsd-current@freebsd.org Subject: gdb bug w/ dlopen()ed images Message-ID: <20000825004231.A89090@unx.sas.com>
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Hi,
There appears to be a problem with gdb when debugging
dynamically loaded images. On 5.0-current with
sources current and built as of this evenning and a
4.1-STABLE system, the following incorrect result is seen:
%gdb ./testmain
GNU gdb 4.18
(gdb) b main
Breakpoint 1 at 0x804853f: file testmain.c, line 11.
(gdb) run
Starting program: /usr/home/jwd/src/ldt/./testmain
Breakpoint 1, main () at testmain.c:11
11 addr = dlopen("./first", RTLD_LAZY);
(gdb) n
13 if (!addr) {
(gdb) n
18 fp = dlsym(addr, "first");
(gdb) n
20 (*fp)();
(gdb) s
0x280f85b7 in first () at first.c:24
24 }
built with gcc version 2.95.2 19991024 (release)
The same test program run under gcb on 4.0-20000313-SNAP
and 4.0-STABLE systems yield the correct result:
%gdb ./testmain
GNU gdb 4.18
(gdb) b main
Breakpoint 1 at 0x80484ff: file testmain.c, line 11.
(gdb) run
Starting program: /usr00/home/jwd/ldt/./testmain
Breakpoint 1, main () at testmain.c:11
11 addr = dlopen("./first", RTLD_LAZY);
(gdb) n
13 if (!addr) {
(gdb) n
18 fp = dlsym(addr, "first");
(gdb) n
20 (*fp)();
(gdb) s
first () at first.c:10
10 addr = dlopen("./second", RTLD_LAZY);
built with gcc version 2.95.2 19991024 (release).
In looking at the stabs information, for the working
version, we find:
STABS> name=first:F(0,1), type=24, desc=6, value=896
STABS> name=, type=44, desc=6, value=0
STABS> name=, type=44, desc=7, value=7
STABS> name=, type=44, desc=10, value=7
STABS> name=, type=44, desc=12, value=30
STABS> name=, type=44, desc=13, value=36
STABS> name=, type=44, desc=14, value=60
STABS> name=, type=44, desc=17, value=76
STABS> name=, type=44, desc=19, value=99
STABS> name=, type=44, desc=21, value=104
STABS> name=, type=44, desc=23, value=119
STABS> name=, type=44, desc=24, value=123
STABS> name=, type=44, desc=24, value=123
STABS> name=first:F(0,1), type=24, desc=6, value=896
and the non-working stabs:
STABS> name=first:F(0,1), type=24, desc=6, value=0
STABS> name=, type=44, desc=6, value=0
STABS> name=, type=44, desc=7, value=7
STABS> name=, type=44, desc=10, value=7
STABS> name=, type=44, desc=12, value=30
STABS> name=, type=44, desc=13, value=36
STABS> name=, type=44, desc=14, value=60
STABS> name=, type=44, desc=17, value=76
STABS> name=, type=44, desc=19, value=99
STABS> name=, type=44, desc=21, value=104
STABS> name=, type=44, desc=23, value=119
STABS> name=, type=44, desc=24, value=123
STABS> name=, type=44, desc=24, value=123
STABS> name=first:F(0,1), type=24, desc=6, value=0
Note that in the non-working version, the only
difference is the value of 896 vs 0. 896 should be the
start address of the function. There is a possibly
relative commment in section G.2 of 'The "stabs" debug format'
put out by Cygnus Support:
http://sources.redhat.com/cygwin/stabs.html#SEC89
It seems to imply that a value=0 field should be
a linker relocated stab.
The test program(s) are simple and can be found at:
http://people.freebsd.org/~jwd/ldt/
I've searched through the PR database but I can't find any
entries that seem related (but then I'm not a GNATS expert either).
If anyone knows anything or has any ideas on this, please let
me know.
Thanks!
John
--
FreeBSD... The choice of those who know how to choose... (anon)
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