[PATCH] gdbserver gnu/linux: stepping over breakpoint

[Yao Qi <qiyaoltc at gmail dot com>]

From: Yao Qi <yao.qi@linaro.org>

Hi,
I see the following error on arm linux gdbserver,

continue^M
Continuing.^M
../../../binutils-gdb/gdb/gdbserver/linux-arm-low.c:458: A problem internal to GDBserver has been detected.^M
raw_bkpt_type_to_arm_hwbp_type: unhandled raw type^M
Remote connection closed^M
(gdb) FAIL: gdb.base/cond-eval-mode.exp: hbreak: continue

After we make GDBserver handling Zx/zx packet idempotent,

  [PATCH 3/3] [GDBserver] Make Zx/zx packet handling idempotent.
  https://sourceware.org/ml/gdb-patches/2014-04/msg00480.html

> Now removal/insertion of all kinds of breakpoints/watchpoints, either
> internal, or from GDB, always go through the target methods.

GDBserver handles all kinds of breakpoints/watchpoints through target
methods.  However, some target backends, such as arm, don't support Z0
packet but need software breakpoint to do breakpoint stepping over in
linux-low.c:start_step_over,

  if (can_hardware_single_step ())
    {
      step = 1;
    }
  else
    {
      CORE_ADDR raddr = (*the_low_target.breakpoint_reinsert_addr) ();
      set_reinsert_breakpoint (raddr);
      step = 0;
    }

a software breakpoint is requested to the backend, and the error is
triggered.  This problem should affect targets having
breakpoint_reinsert_addr hooked.

Instead of handling memory breakpoint in these affected linux backend,
this patch handles memory breakpoint in linux_{insert,remove}_point,
that, if memory breakpoint is requested, call
{insert,remove}_memory_breakpoint respectively.  Then, it becomes
unnecessary to handle memory breakpoint for linux x86 backend, so
this patch removes the code there.

This patch is tested with GDBserver on x86_64-linux and arm-linux
(-marm, -mthumb).  Testing this patch on mips, nios2, bfin, and sparc
is welcome.

Note that there are still some fails in gdb.base/cond-eval-mode.exp
with -mthumb, because GDBserver doesn't know how to select the
correct breakpoint instruction according to the arm-or-thumb-mode of
requested address.  This is a separate issue, anyway.

gdb/gdbserver:

2015-04-09  Yao Qi  <yao.qi@linaro.org>

	* linux-low.c (linux_insert_point): Call
	insert_memory_breakpoint if TYPE is raw_bkpt_type_sw.
	(linux_remove_point): Call remove_memory_breakpoint if type is
	raw_bkpt_type_sw.
	* linux-x86-low.c (x86_insert_point): Don't call
	insert_memory_breakpoint.
	(x86_remove_point): Don't call remove_memory_breakpoint.
---
 gdb/gdbserver/linux-low.c     | 8 ++++++--
 gdb/gdbserver/linux-x86-low.c | 6 ------
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index e4c5420..6dd9224 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -5115,7 +5115,9 @@ static int
 linux_insert_point (enum raw_bkpt_type type, CORE_ADDR addr,
 		    int size, struct raw_breakpoint *bp)
 {
-  if (the_low_target.insert_point != NULL)
+  if (type == raw_bkpt_type_sw)
+    return insert_memory_breakpoint (bp);
+  else if (the_low_target.insert_point != NULL)
     return the_low_target.insert_point (type, addr, size, bp);
   else
     /* Unsupported (see target.h).  */
@@ -5126,7 +5128,9 @@ static int
 linux_remove_point (enum raw_bkpt_type type, CORE_ADDR addr,
 		    int size, struct raw_breakpoint *bp)
 {
-  if (the_low_target.remove_point != NULL)
+  if (type == raw_bkpt_type_sw)
+    return remove_memory_breakpoint (bp);
+  else if (the_low_target.remove_point != NULL)
     return the_low_target.remove_point (type, addr, size, bp);
   else
     /* Unsupported (see target.h).  */
diff --git a/gdb/gdbserver/linux-x86-low.c b/gdb/gdbserver/linux-x86-low.c
index e293ba4..763df08 100644
--- a/gdb/gdbserver/linux-x86-low.c
+++ b/gdb/gdbserver/linux-x86-low.c
@@ -561,9 +561,6 @@ x86_insert_point (enum raw_bkpt_type type, CORE_ADDR addr,
 
   switch (type)
     {
-    case raw_bkpt_type_sw:
-      return insert_memory_breakpoint (bp);
-
     case raw_bkpt_type_hw:
     case raw_bkpt_type_write_wp:
     case raw_bkpt_type_access_wp:
@@ -590,9 +587,6 @@ x86_remove_point (enum raw_bkpt_type type, CORE_ADDR addr,
 
   switch (type)
     {
-    case raw_bkpt_type_sw:
-      return remove_memory_breakpoint (bp);
-
     case raw_bkpt_type_hw:
     case raw_bkpt_type_write_wp:
     case raw_bkpt_type_access_wp:
-- 
1.9.1