[PATCH][gdb/tdep, rs6000] Don't skip system call in skip_prologue

[Tom de Vries <tdevries@suse.de>]

Hi,

I ran into a case where a breakpoint on _exit never triggered, because it was
set past the end of the _exit prologue, past the end of the exit_group system
call (which does not return).

Fix this by treating system calls the same as branches in skip_prologue:
by default, don't skip.

Tested on ppc64le-linux, on a power 8 machine.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28527

Any comments?

Thanks,
- Tom

[gdb/tdep, rs6000] Don't skip system call in skip_prologue

---
 gdb/rs6000-tdep.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
index 78b4fd1a913..4830ed22593 100644
--- a/gdb/rs6000-tdep.c
+++ b/gdb/rs6000-tdep.c
@@ -2137,6 +2137,12 @@ skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc, CORE_ADDR lim_pc,
 	    /* Never skip branches.  */
 	    break;
 
+	  /* Test based on opcode and mask values of
+	     powerpc_opcodes[svc..svcla] in opcodes/ppc-opc.c.  */
+	  if ((op & 0xffff0000) == 0x44000000)
+	    /* Never skip system calls.  */
+	    break;
+
 	  if (num_skip_non_prologue_insns++ > max_skip_non_prologue_insns)
 	    /* Do not scan too many insns, scanning insns is expensive with
 	       remote targets.  */