Don't suppress errors inserting/removing hardware breakpoints in shared

libraries.

As explained in
https://sourceware.org/ml/gdb-patches/2008-08/msg00361.html, after a
shared library was unloaded, we can no longer insert or remove
breakpoints into/from its (no longer present) code segment.  That'll
fail with memory errors.  However, that concern does not apply to
hardware breakpoints.  By definition, hardware breakpoints are
implemented using a mechanism that is not dependent on being able to
modify the target's memory.  Usually, by setting up CPU debug
registers.  IOW, we should be able to set hw breakpoints in an
unmapped address.  We don't seem to have a test that exercises that,
so this patch adds one.

I noticed the error supression because of a related issue -- the
target_insert_hw_breakpoint/target_remove_hw_breakpoint interfaces
don't really distinguish "not supported" from "error" return, and so
remote.c returns -1 in both cases.  This results in hardware
breakpoints set in shared libraries silently ending up pending forever
even though the target doesn't actually support hw breakpoints.

 (gdb) set breakpoint always-inserted on
 (gdb) set remote Z-packet off
 (gdb) info breakpoints
 No breakpoints or watchpoints.
 (gdb) hbreak shrfunc
 Hardware assisted breakpoint 3 at 0x7ffff7dfb657: file ../../../src/gdb/testsuite/gdb.base/hbreak-in-shr-unsupported-shr.c, line 21.
 (gdb) info break
 Num     Type           Disp Enb Address            What
 3       hw breakpoint  keep y   <PENDING>          shrfunc

After the patch we get the expected:

 (gdb) hbreak shrfunc
 Hardware assisted breakpoint 3 at 0x7ffff7dfb657: file ../../../src/gdb/testsuite/gdb.base/hbreak-in-shr-unsupported-shr.c, line 21.
 Warning:
 Cannot insert hardware breakpoint 3.
 Could not insert hardware breakpoints:
 You may have requested too many hardware breakpoints/watchpoints.

 (gdb) info break
 Num     Type           Disp Enb Address            What
 3       hw breakpoint  keep y   0x00007ffff7dfb657 in shrfunc at ../../../src/gdb/testsuite/gdb.base/hbreak-in-shr-unsupported-shr.c:21

(HW breakpoints set in the main executable, when the target doesn't
support HW breakpoints always resulted in the latter output.)

We probably should improve the insert/remove interface to return a
different error code for unsupported.  But I chose to fix the error
supression first, as it's a deeper and wider issue.

Tested on x86_64 Fedora 17, native and gdbserver.

gdb/
2014-04-23  Pedro Alves  <palves@redhat.com>

	* breakpoint.c (insert_bp_location, remove_breakpoint_1): If
	the breakpoint is set in a shared library, only suppress
	errors for software breakpoints, not hardware breakpoints.

gdb/testsuite/
2014-04-23  Pedro Alves  <palves@redhat.com>

	* gdb.base/hbreak-in-shr-unsupported-shr.c: New file.
	* gdb.base/hbreak-in-shr-unsupported.c: New file.
	* gdb.base/hbreak-in-shr-unsupported.exp: New file.
	* gdb.base/hbreak-unmapped.c: New file.
	* gdb.base/hbreak-unmapped.exp: New file.
	* gdb.trace/qtro.exp (gdb_is_target_remote): Move ...
	* lib/gdb.exp (gdb_is_target_remote): ... here.

1 files changed, 8 insertions, 6 deletions

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index f777a4a..19a7376 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -2642,12 +2642,12 @@ insert_bp_location (struct bp_location *bl,
 	     breakpoint in a shared library that has already been
 	     removed, but we have not yet processed the shlib unload
 	     event.  Unfortunately, some targets that implement
-	     breakpoint insertion themselves (necessary if this is a
-	     HW breakpoint, but SW breakpoints likewise) can't tell
-	     why the breakpoint insertion failed (e.g., the remote
-	     target doesn't define error codes), so we must treat
-	     generic errors as memory errors.  */
+	     breakpoint insertion themselves can't tell why the
+	     breakpoint insertion failed (e.g., the remote target
+	     doesn't define error codes), so we must treat generic
+	     errors as memory errors.  */
 	  if ((bp_err == GENERIC_ERROR || bp_err == MEMORY_ERROR)
+	      && bl->loc_type == bp_loc_software_breakpoint
 	      && solib_name_from_address (bl->pspace, bl->address))
 	    {
 	      /* See also: disable_breakpoints_in_shlibs.  */
@@ -3826,7 +3826,9 @@ remove_breakpoint_1 (struct bp_location *bl, insertion_state_t is)
       /* In some cases, we might not be able to remove a breakpoint
 	 in a shared library that has already been removed, but we
 	 have not yet processed the shlib unload event.  */
-      if (val && solib_name_from_address (bl->pspace, bl->address))
+      if (val
+	  && bl->loc_type == bp_loc_software_breakpoint
+	  && solib_name_from_address (bl->pspace, bl->address))
 	val = 0;
 
       if (val)