* Why running the next command will jump back to the previous line position
@ 2011-10-29 7:23 asmwarrior
2011-10-29 7:42 ` Jan Kratochvil
0 siblings, 1 reply; 6+ messages in thread
From: asmwarrior @ 2011-10-29 7:23 UTC (permalink / raw)
To: gdb
Hi, I'm using MinGW 4.6.2 and GDB cvs head under Windows XP.
When debugging a sample program: (I build it with -g, and no optimization option is used)
#include <string>
#include <map>
int main()
{
std::map<int, std::string> m;
m[0] = "000";
m[1] = "111";
for( int i = 0; i< 3; i++)
{
m[i] = "ssss";
}
return 0;
}
If I continuously run the command "next" under gdb, I found that when I hit the statement "return 0", if I run "next" again, It will take me backward to the line "std::map<int, std::string> m;". If I run the "next" again, the instruction will go forward the closing bracket of the main function body.
This was quite strange, it looks like the instruction will return to some previous position. (I guess that the destructor of the "std::map" was called.
My question is: This behavior is quite anti-friendly, because if I'm debugging a large function, I always get the instruction line back to where some local variable (automatic variable) was defined.
Is it possible to solve it. I don't want the instruction line go backward when I leave some scope.
Thanks.
asmwarrior
ollydbg from codeblocks' forum
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: Why running the next command will jump back to the previous line position 2011-10-29 7:23 Why running the next command will jump back to the previous line position asmwarrior @ 2011-10-29 7:42 ` Jan Kratochvil 2011-10-29 7:49 ` asmwarrior 0 siblings, 1 reply; 6+ messages in thread From: Jan Kratochvil @ 2011-10-29 7:42 UTC (permalink / raw) To: asmwarrior; +Cc: gdb On Sat, 29 Oct 2011 09:11:25 +0200, asmwarrior wrote: [...] > This was quite strange, it looks like the instruction will return to some > previous position. (I guess that the destructor of the "std::map" was > called. yes, objdump -dSC shows there: std::map<int, std::string> m; 400bab: 48 8d 45 b0 lea -0x50(%rbp),%rax 400baf: 48 89 c7 mov %rax,%rdi 400bb2: e8 43 00 00 00 callq 400bfa <std::map<int, std::string, std::less<int>, std::allocator<std::pair<int const, std::string> > >::~map()> 400bb7: 89 d8 mov %ebx,%eax > My question is: This behavior is quite anti-friendly, Maybe GCC could produce there DW_LNS_negate_stmt so that the variable declaration line is still shown in backtraces (if the destructor crashes) but it is skipped over during stepping/nexting; but GDB currently would not show such line in backtraces, GCC currently does not produce DW_LNS_negate_stmt anyway. Regards, Jan ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Why running the next command will jump back to the previous line position 2011-10-29 7:42 ` Jan Kratochvil @ 2011-10-29 7:49 ` asmwarrior 2011-10-29 10:39 ` Jan Kratochvil 2011-10-29 14:14 ` 陳韋任 0 siblings, 2 replies; 6+ messages in thread From: asmwarrior @ 2011-10-29 7:49 UTC (permalink / raw) To: Jan Kratochvil; +Cc: gdb On 2011-10-29 15:22, Jan Kratochvil wrote: > On Sat, 29 Oct 2011 09:11:25 +0200, asmwarrior wrote: > [...] >> This was quite strange, it looks like the instruction will return to some >> previous position. (I guess that the destructor of the "std::map" was >> called. > > yes, objdump -dSC shows there: > > std::map<int, std::string> m; > 400bab: 48 8d 45 b0 lea -0x50(%rbp),%rax > 400baf: 48 89 c7 mov %rax,%rdi > 400bb2: e8 43 00 00 00 callq 400bfa<std::map<int, std::string, std::less<int>, std::allocator<std::pair<int const, std::string> > >::~map()> > 400bb7: 89 d8 mov %ebx,%eax > Hi, thanks for the reply, I just run the objdump -dSC a.exe under Windows, and I found the similar content. So, it looks like the line "std::map<int, std::string> m;" associates many instruction pieces. Those pieces include the calling of the std::map's destructor. When leaving the main function body, the instruction piece of the destructor will reached, and gdb just refer to the declaration line. So that gdb put the current source line back to "std::map<int, std::string> m;" again. My explanation is right? > >> My question is: This behavior is quite anti-friendly, > > Maybe GCC could produce there DW_LNS_negate_stmt so that the variable > declaration line is still shown in backtraces (if the destructor crashes) but > it is skipped over during stepping/nexting; but GDB currently would not show > such line in backtraces, GCC currently does not produce DW_LNS_negate_stmt > anyway. > I'm not quite sure what DW_LNS_negate_stmt means, any way, I will forward my question to GCC maillist. Thanks. asmwarrior ollydbg from codeblocks' forum ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Why running the next command will jump back to the previous line position 2011-10-29 7:49 ` asmwarrior @ 2011-10-29 10:39 ` Jan Kratochvil 2011-10-29 14:14 ` 陳韋任 1 sibling, 0 replies; 6+ messages in thread From: Jan Kratochvil @ 2011-10-29 10:39 UTC (permalink / raw) To: asmwarrior; +Cc: gdb On Sat, 29 Oct 2011 09:45:41 +0200, asmwarrior wrote: > When leaving the main function body, the instruction piece of the destructor > will reached, and gdb just refer to the declaration line. So that gdb put > the current source line back to "std::map<int, std::string> m;" again. > > My explanation is right? yes. > I'm not quite sure what DW_LNS_negate_stmt means, any way, I will forward my > question to GCC maillist. DWARF: is_stmt A boolean indicating that the current instruction is a recommended breakpoint location. A recommended breakpoint location is intended to “represent” a line, a statement and/or a semantically distinct subpart of a statement. I am not convinced myself it is right to hide destructor calls; but I am not C++ developer. Regards, Jan ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Why running the next command will jump back to the previous line position 2011-10-29 7:49 ` asmwarrior 2011-10-29 10:39 ` Jan Kratochvil @ 2011-10-29 14:14 ` 陳韋任 2011-10-29 17:12 ` asmwarrior 1 sibling, 1 reply; 6+ messages in thread From: 陳韋任 @ 2011-10-29 14:14 UTC (permalink / raw) To: asmwarrior; +Cc: Jan Kratochvil, gdb > > Maybe GCC could produce there DW_LNS_negate_stmt so that the variable > > declaration line is still shown in backtraces (if the destructor crashes) but > > it is skipped over during stepping/nexting; but GDB currently would not show > > such line in backtraces, GCC currently does not produce DW_LNS_negate_stmt > > anyway. > > > > I'm not quite sure what DW_LNS_negate_stmt means, any way, I will forward my question to GCC maillist. GCC should emit debug information so that GDB can work correctly. You can checkout http://dwarfstd.org/doc/Dwarf3.pdf . Regards, chenwj -- Wei-Ren Chen (陳韋任) Computer Systems Lab, Institute of Information Science, Academia Sinica, Taiwan (R.O.C.) Tel:886-2-2788-3799 #1667 ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Why running the next command will jump back to the previous line position 2011-10-29 14:14 ` 陳韋任 @ 2011-10-29 17:12 ` asmwarrior 0 siblings, 0 replies; 6+ messages in thread From: asmwarrior @ 2011-10-29 17:12 UTC (permalink / raw) To: Jan Kratochvil, gdb On 2011-10-29 18:39, 陳韋任 wrote: >>> Maybe GCC could produce there DW_LNS_negate_stmt so that the variable >>> declaration line is still shown in backtraces (if the destructor crashes) but >>> it is skipped over during stepping/nexting; but GDB currently would not show >>> such line in backtraces, GCC currently does not produce DW_LNS_negate_stmt >>> anyway. >>> >> >> I'm not quite sure what DW_LNS_negate_stmt means, any way, I will forward my question to GCC maillist. > > GCC should emit debug information so that GDB can work correctly. > You can checkout http://dwarfstd.org/doc/Dwarf3.pdf . > > Regards, > chenwj > Well, thanks. It looks like there is a similar gcc bug report. see: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49951 It looks like at this revision: http://gcc.gnu.org/viewcvs?view=revision&revision=149722 I have no experience to dig into gcc source.... Hope the GCC guys can help. asmwarrior ollydbg from codeblocks' forum ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2011-10-29 14:14 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2011-10-29 7:23 Why running the next command will jump back to the previous line position asmwarrior 2011-10-29 7:42 ` Jan Kratochvil 2011-10-29 7:49 ` asmwarrior 2011-10-29 10:39 ` Jan Kratochvil 2011-10-29 14:14 ` 陳韋任 2011-10-29 17:12 ` asmwarrior
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