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

Pedro Alves
2015-07-06T16:15:19Z

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.

> 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

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?

---
From 9cbd03b61441072c71d2076c1deb6766fecf25d2 Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Mon, 6 Jul 2015 17:04:05 +0100
Subject: [PATCH] remove left behind permanent breakpoint special casing

---
gdb/breakpoint.c | 11 +----------
1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index 1481112..af0d167 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -3892,10 +3892,6 @@ remove_breakpoint_1 (struct bp_location *bl, insertion_state_t is)
/* BL is never in moribund_locations by our callers. */
gdb_assert (bl->owner != NULL);

- if (bl->permanent)
- /* Permanent breakpoints cannot be inserted or removed. */
- return 0;
-
/* The type of none suggests that owner is actually deleted.
This should not ever happen. */
gdb_assert (bl->owner->type != bp_none);
@@ -4042,10 +4038,6 @@ remove_breakpoint (struct bp_location *bl, insertion_state_t is)
/* BL is never in moribund_locations by our callers. */
gdb_assert (bl->owner != NULL);

- if (bl->permanent)
- /* Permanent breakpoints cannot be inserted or removed. */
- return 0;
-
/* The type of none suggests that owner is actually deleted.
This should not ever happen. */
gdb_assert (bl->owner->type != bp_none);
@@ -4068,8 +4060,7 @@ mark_breakpoints_out (void)
struct bp_location *bl, **blp_tmp;

ALL_BP_LOCATIONS (bl, blp_tmp)
- if (bl->pspace == current_program_space
- && !bl->permanent)
+ if (bl->pspace == current_program_space)
bl->inserted = 0;
}

--
1.9.3