Re: [patch] XFAIL gdb.cp/mb-inline.exp conditionaly

Pedro Alves
2011-06-23T10:28:32Z

On Thursday 23 June 2011 10:21:21, Yao Qi wrote:
> On 06/22/2011 11:38 PM, Pedro Alves wrote:

> > The breakpoint was set by line number, and we're reloading
> > the session the same both times. Why does breakpoint 1.2 become
> > enabled (and I'm guessing that breakpoint 1.1 becomes disabled)?
> >
>
> No, in my case, both 1.1 and 1.2 becomes enabled.
> info break^M
> Num Type Disp Enb Address What^M
> 1 breakpoint keep y <MULTIPLE> ^M
> breakpoint already hit 3 times^M
> 1.1 y 0xe78c90a8 in foo(int) at
> gdb/testsuite/gdb.cp/mb-inline.h:26^M
> 1.2 y 0xe78c91a8 in foo(int) at
> gdb/testsuite/gdb.cp/mb-inline.h:26^M
>
> During breakpoint updates (when inferior is re-created), GDB will
> iterate list of breakpoint locations, to look for breakpoint locations
> for a certain address in new inferior, and assign found breakpoint
> locations to that breakpoint. The state of breakpoint location
> (enabled/disabled) is kept, and this test will pass.
>
> If gdb is unable to find any breakpoint location for a given address,
> gdb will create new breakpoint locations, and remove old breakpoint
> location. Then, the state of breakpoint location of previous inferior
> is lost, and new created breakpoint location is enabled in default.

Okay, that happens when the locations have ambiguous names, at the
end of update_breakpoint_locations.

You're just re-running the same binary, and the breakpoints are even
all set in the same objfile. Nothing changed from the user's
perpective. It's reasonable to expect gdb manages to not lose track
of the disable state. I think we can and should improve the heuristic
to handle this scenario.

Instead of comparing
absolute addresses, normalize them before comparing. E.g.,

Before After
0x400010 0x800010
0x401000 0x801000
0x410000 0x810000
0x400100 0x800100

For each list, find some common base and subtract it from
each entry, and _then_ compare the locations:

Before After
0x000010 0x000010
0x001000 0x001000
0x010000 0x010000
0x000100 0x000100

The common base might be the lowest address in each list,
or something else, like the objfile's lowest address, or
some such. If we had some sort of unique symbol hash id,
we could use that instead, and it'd be more reliable, me
thinks.

--
Pedro Alves