On 06/09/2015 04:00 PM, Luis Machado wrote:
This is in line with what was done by Joel's patch here:
https://sourceware.org/ml/gdb-patches/2014-11/msg00478.html
And it also answers Pedro's question about whether this is specific to SPARC
QEMU or not. This indeed seems to affect multiple QEMU targets and also other
simulators (proprietary).
Sounds like a different issue, although related.
I ran into this weird issue of not being able to "finish" an inferior function
call. It looks as if the program is running away, but it really is stuck
somewhere. "finish" still works fine for regular functions not called manually
by GDB.
Sounds like that would fail on SPARC qemu as well.
I tracked this failure down to GDB having both a bp_call_dummy and bp_finish in
its breakpoint list. As a result of one not being considered permanent and the
other considered permanent, GDB will not issue a Z packet to force the insertion
of that location's breakpoint, confusing the simulator that does not know how
to deal properly with these permanent breakpoints that GDB inserted beforehand.
The attached patch fixes this, though i'm inclined to say we could probably
check if both bp_call_dummy and bp_finish are present and force the
insertion of that location's breakpoint. It isn't clear to me where exactly that
check would go or if it would be cleaner than checking that information in
the same function Joel used.
I see no regressions on x86-64 and it fixes a bunch of failures for simulator
targets we use (MIPS and PowerPC to name two).
If it happens that you "finish" from a normal function, and the finish
breakpoint ends up on top of a real permanent breakpoint, then this patch
will make us end up inserting a breakpoint on top of that permanent
breakpoint. I don't see what's special about finish breakpoints;
it's the address (dummy breakpoint location) that is special. It very much
sounds like that any kind of breakpoint that is placed on top of the dummy
breakpoint ends up with the same issue. E.g., if you stepi out of
the called function, with a software single-step breakpoint, sounds like
GDB will miss inserting the software step breakpoint because that's
at the same address as the dummy breakpoint.