Date: Thu, 3 Aug 2000 16:01:42 +1000 (EST) From: Andy Newman <andy@silverbrook.com.au> To: FreeBSD-gnats-submit@freebsd.org Subject: bin/20373: Setting breakpoints in shared objects broken Message-ID: <200008030601.QAA20818@bebop.lan.silverbrook.com.au>
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>Number: 20373
>Category: bin
>Synopsis: Setting breakpoints in shared objects broken
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Wed Aug 02 23:10:00 PDT 2000
>Closed-Date:
>Last-Modified:
>Originator: Andy Newman
>Release: FreeBSD 4.1-STABLE i386
>Organization:
Silverbrook Research
>Environment:
Freshly CVSup'd 4.1-STABLE as of Aug. 3, 13:00 (GMT +10),
$ uname -a
FreeBSD bebop.lan.silverbrook.com.au 4.1-STABLE FreeBSD 4.1-STABLE #0: Thu Aug 3 13:29:45 EST 2000 toor@bebop.lan.silverbrook.com.au:/usr/obj/usr/src/sys/bebop i386
(i.e., cvsup & make buildworld approx. three hours prior to bug submission)
Problem also occurs on a slighly older 4.0-STABLE (post-release CVSup)
but *does not* occur on a 3.5-STABLE system.
>Description:
Setting a breakpoint in an run-time loaded object from a
C or C++ program does not work as expected. The breakpoint
appears to be set at the end of the function or at least
the trap doesn't occur until function exit rather than
at the breakpoint position. See following typscript of
a debug session using the attached sample program which
loads a shared object and calls a function. The sample is
C++ (as that is where I first ran into the problem) but
compiling it as C (with a couple of little mods) shows
the same problem.
This behaviour seems to have occurred *after* 4.0-RELEASE.
Script started on Thu Aug 3 15:34:59 2000
: bebop; make clean all
rm -f tst so.so
c++ -g -o tst tst.cpp
c++ -g -shared -o so.so so.cpp
: bebop; gdb tst
GNU gdb 4.18
Copyright 1998 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "i386-unknown-freebsd"...
(gdb) set environment LD_LIBRARY_PATH .
(gdb) b dlopen
Breakpoint 1 at 0x8048814
(gdb) r so.so func
Starting program: /home/andy/tmp/bugs/c++-gdb-breakpoint/tst so.so func
Breakpoint 1 at 0x280f7c4f
Breakpoint 1 at 0x280520dd
Breakpoint 1, 0x280520dd in dlopen () from /usr/libexec/ld-elf.so.1
(gdb) fin
Run till exit from #0 0x280520dd in dlopen () from /usr/libexec/ld-elf.so.1
0x8048993 in main (argc=3, argv=0xbfbff308) at tst.cpp:14
14 if ((h = dlopen(argv[1], RTLD_NOW)) == NULL)
(gdb) shared
Symbols already loaded for /usr/lib/libstdc++.so.3
Symbols already loaded for /usr/lib/libm.so.2
Symbols already loaded for /usr/lib/libc.so.4
Symbols already loaded for /home/andy/tmp/bugs/c++-gdb-breakpoint/./so.so
Symbols already loaded for /usr/libexec/ld-elf.so.1
(gdb) b func
Breakpoint 2 at 0x281554be: file so.cpp, line 12.
(gdb) c
Continuing.
Breakpoint 2, 0x281554be in func () at so.cpp:12
12 } <==== last line of func()
(gdb) where
#0 0x281554be in func () at so.cpp:12
#1 0x8048a0d in main (argc=3, argv=0xbfbff308) at tst.cpp:18
#2 0x80488f1 in _start ()
(gdb) step
... func() executes
main (argc=3, argv=0xbfbff308) at tst.cpp:19
19 if (dlclose(h) == -1)
(gdb) cont
(deletia)
Script done on Thu Aug 3 15:36:13 2000
>How-To-Repeat:
See attached shar file. It has a simple test program that
loads a shared object and calls a function in it. If you
debug this, set a break point on dlopen and "fin" from it
so the loaded object's symbols are loaded, then set a break
point on "func" and continue. The break point doesn't
occur until the function exits.
# This is a shell archive. Save it in a file, remove anything before
# this line, and then unpack it by entering "sh file". Note, it may
# create directories; files and directories will be owned by you and
# have default permissions.
#
# This archive contains:
#
# Makefile
# so.cpp
# tst.cpp
#
echo x - Makefile
sed 's/^X//' >Makefile << 'END-of-Makefile'
Xall: tst so.so
X
Xtst: tst.cpp
X c++ -g -o $@ tst.cpp
X
Xso.so: so.cpp
X c++ -g -shared -o $@ so.cpp
X
Xtest:
X @LD_LIBRARY_PATH=`pwd` ./tst so.so func
X
Xclean:
X rm -f tst so.so
END-of-Makefile
echo x - so.cpp
sed 's/^X//' >so.cpp << 'END-of-so.cpp'
X#include <stdio.h>
X
Xextern "C"
Xvoid
Xfunc()
X{
X for (int i = 0; i < 10; ++i)
X printf(".");
X printf("In function");
X for (int i = 0; i < 10; ++i)
X printf(".");
X printf("\n");
X}
END-of-so.cpp
echo x - tst.cpp
sed 's/^X//' >tst.cpp << 'END-of-tst.cpp'
X#include <stdio.h>
X#include <dlfcn.h>
X#include <err.h>
X
Xint
Xmain(int argc, char **argv)
X{
X void *h;
X void (*fn)();
X
X if (argc != 3)
X errx(1, "usage: %s so ident", argv[0]);
X if ((h = dlopen(argv[1], RTLD_NOW)) == NULL)
X errx(1, "can't dlopen %s: %s", argv[1], dlerror());
X if ((fn = (void (*)())dlsym(h, argv[2])) == NULL)
X errx(2, "can't dlsym %s : %s", argv[2], dlerror());
X (*fn)();
X if (dlclose(h) == -1)
X errx(3, "dlclose failed: %s", dlerror());
X return 0;
X}
END-of-tst.cpp
exit
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted:
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