Re: [PATCH] Fix problems with finishing a dummy function call on simulators.

Luis Machado
2015-07-06T16:18:22Z

On 07/06/2015 01:15 PM, Pedro Alves wrote:
> On 07/06/2015 04:33 PM, Luis Machado wrote:
>
>> I'll take a look at it. I suppose this will block the branching?
>
> I think so, or at least the release. Broken infcalls seems
> pretty nasty.
>

Indeed.

>> Then again, simply reverting this will still have bad results with some
>> simulators.
>
> True. Might be the fix is simple though. I'm seeing this:
>
> (gdb) PASS: gdb.base/shlib-call.exp: step out of shr2 to main (stopped in shr2 epilogue)
> step
> main () at /home/pedro/gdb/mygit/build/../src/gdb/testsuite/gdb.base/shmain.c:37
> 37 g = mainshr1(g);
> (gdb) PASS: gdb.base/shlib-call.exp: step out of shr2 epilogue to main
> print mainshr1(1)
>
> Program received signal SIGSEGV, Segmentation fault.
> mainshr1 (g=1) at /home/pedro/gdb/mygit/build/../src/gdb/testsuite/gdb.base/shmain.c:29
> 29 }
> The program being debugged was signaled while in a function called from GDB.
> GDB remains in the frame where the signal was received.
> To change this behavior use "set unwindonsignal on".
> Evaluation of the expression containing the function
> (mainshr1) will be abandoned.
> When the function is done executing, GDB will silently stop.
> (gdb) FAIL: gdb.base/shlib-call.exp: print mainshr1(1)
> step
>

That's what i see too.

> The SIGSEGV look scary until one remembers that the dummy breakpoints
> are placed on the stack, which is non-executable. gdb translates those
> SIGSEGVs back to SIGTRAPs, provided it knows there's a breakpoint at that
> address.
>
> Looking a bit at breakpoint.c, I notice that a few ->permanent
> checks seem to have been left behind, and as result we don't actually
> remove from the target the breakpoints that were placed on top of the
> permanent breakpoints?
>
> This seems to fix the FAILs here, but I didn't run full regression
> testing. Could you take this, test it on qemu, and and finish it off?
>

Yes, of course. Thanks for having a go at it.

Luis