https://bugs.kde.org/show_bug.cgi?id=384368
Bug ID: 384368
Summary: Support for gdb watchpoint option -location
Product: kdevelop
Version: unspecified
Platform: unspecified
OS: Linux
Status: UNCONFIRMED
Severity: normal
Priority: NOR
Component: CPP Debugger
Assignee: kdevelop-bugs-n...@kde.org
Reporter: 7437...@gmail.com
CC: niko.s...@gmail.com
Target Milestone: ---
Copying from mailing list thread
https://mail.kde.org/pipermail/kdevelop/2017-September/019479.html:
> I've set watchpoint with command `watch -l` and it was saved in KDevelop
> session. Now it doesn't start debug session because it ends up in endless
> loop:
> (gdb) 2106-break-watch "-location m_part_spec.start_part"
> 2106^error,msg="-break-watch: Unknown option ``location
> m_part_spec.start_part''"
> (gdb) 2107-break-watch "-location m_part_spec.start_part"
> 2107^error,msg="-break-watch: Unknown option ``location
> m_part_spec.start_part''"
> (gdb) 2108-break-watch "-location m_part_spec.start_part"
> 2108^error,msg="-break-watch: Unknown option ``location
> m_part_spec.start_part''"
> (gdb) 2109-break-watch "-location m_part_spec.start_part"
> 2109^error,msg="-break-watch: Unknown option ``location
> m_part_spec.start_part''"
> (gdb) 2110-break-watch "-location m_part_spec.start_part"
> 2110^error,msg="-break-watch: Unknown option ``location
> m_part_spec.start_part''"
1. BreakpointModel gets updated when user creating watch points directly using
command. The location reported by GDB includes the "-location " part, but since
we are quoting the entire string, GDB interprets the entire string as an
option, rather than only the "-location" part.
2. Even though we recognize the location and only quote remaining expression,
GDB/MI which is the protocol we use to communicate with GDB actually doesn't
support "-l/-location" option. see [1]
3. When starts new session, KDevelop tries to automatically reapply all
break/watch points saved in BreakpointModel. But the command fails due to above
reason. However there shouldn't be an endless loop. Once the command fails, it
should set the error message in the Breakpoint toolview and continue. But maybe
I'm just missing something.
The fix would be
1. In mibreakpointcontroller.cpp:358, detect and quote only the expression
part, this is easy.
2. Find a way to emulate the "-location" option. Possible solutions:
2.1 Take the address of the expression when watch point got set and save
that in BreakpointModel. But addresses are likely to change between runs
2.2 Simply remove "-location" part and set it as a normal watch point. But
likely at the very begining of the program, the expression is out of scope.
2.3 Skip it. IMHO even normal watchpoints should be skipped. As they rely
on expressions that are hardly valid at this time.
3. Desired behavior should be display the error in Breakpoint toolview, rather
than entering an endless loop. However I didn't find which part of the code is
causing the loop after a quick of the codebase. And the desired behavior is
already implemented. This will need more investigation.
[1]
https://sourceware.org/gdb/onlinedocs/gdb/GDB_002fMI-Breakpoint-Commands.html#GDB_002fMI-Breakpoint-Commands
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