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Fix step-over-syscall.exp failure

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In particular, this one:

FAIL: gdb.base/step-over-syscall.exp: fork: displaced=on: check_pc_after_cross_syscall: single step over fork final pc

When ptrace fork event reporting is enabled, GDB gets a PTRACE_EVENT_FORK
event whenever the inferior executes the fork syscall.

Then the logic is that GDB needs to step the inferior yet again in order to
receive a predetermined SIGTRAP, but no execution takes place because the
signal was already queued for delivery. That means the PC should stay the same.

I noticed the aarch64 code is currently adjusting the PC in this situation,
making the inferior skip an instruction without executing it.

The following change checks if we did not execute the instruction
(pc - to == 0), making proper adjustments for such case.

Regression tested on aarch64-linux-gnu on the tryserver.

gdb/ChangeLog:

2020-01-21  Luis Machado  <luis.machado@linaro.org>

	* aarch64-tdep.c (struct aarch64_displaced_step_closure )
	<pc_adjust>: Adjust the documentation.
	(aarch64_displaced_step_fixup): Check if PC really moved before
	adjusting it.
This commit is contained in:
Luis Machado 2020-01-09 16:04:36 -03:00
parent 1a0351246a
commit 0c27188999
2 changed files with 20 additions and 4 deletions
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7
gdb/ChangeLog
View file

@ -1,3 +1,10 @@
2020-01-21 Luis Machado <luis.machado@linaro.org>
* aarch64-tdep.c (struct aarch64_displaced_step_closure )
<pc_adjust>: Adjust the documentation.
(aarch64_displaced_step_fixup): Check if PC really moved before
adjusting it.
2020-01-19 Tom Tromey <tom@tromey.com>
* disasm.c (~gdb_disassembler): New destructor.

17
gdb/aarch64-tdep.c
View file

@ -2737,7 +2737,8 @@ struct aarch64_displaced_step_closure : public displaced_step_closure
is being displaced stepping. */
int cond = 0;
/* PC adjustment offset after displaced stepping. */
/* PC adjustment offset after displaced stepping. If 0, then we don't
write the PC back, assuming the PC is already the right address. */
int32_t pc_adjust = 0;
};
@ -3032,11 +3033,12 @@ aarch64_displaced_step_fixup (struct gdbarch *gdbarch,
{
aarch64_displaced_step_closure *dsc = (aarch64_displaced_step_closure *) dsc_;
ULONGEST pc;
regcache_cooked_read_unsigned (regs, AARCH64_PC_REGNUM, &pc);
if (dsc->cond)
{
ULONGEST pc;
regcache_cooked_read_unsigned (regs, AARCH64_PC_REGNUM, &pc);
if (pc - to == 8)
{
/* Condition is true. */
@ -3052,6 +3054,13 @@ aarch64_displaced_step_fixup (struct gdbarch *gdbarch,
if (dsc->pc_adjust != 0)
{
/* Make sure the previous instruction was executed (that is, the PC
has changed). If the PC didn't change, then discard the adjustment
offset. Otherwise we may skip an instruction before its execution
took place. */
if ((pc - to) == 0)
dsc->pc_adjust = 0;
if (debug_displaced)
{
debug_printf ("displaced: fixup: set PC to %s:%d\n",