[PATCH v2] PR breakpoints/21886: mem-break: Fix breakpoint insertion location

["Maciej W. Rozycki" <macro at imgtec dot com>]

Fix a commit cd6c3b4ffc4e ("New gdbarch methods breakpoint_kind_from_pc 
and sw_breakpoint_from_kind") regression and restore the use of 
`->placed_address' rather than `->reqstd_address' as the location for a 
memory breakpoint to be inserted at.  Previously 
`gdbarch_breakpoint_from_pc' was used that made that adjustment in 
`default_memory_insert_breakpoint' from the preinitialized value, 
however with the said commit that call is gone, so the passed 
`->placed_address' has to be used for the initialization.

The regression manifests itself as the inability to debug any MIPS/Linux 
compressed ISA dynamic executable as GDB corrupts the dynamic loader 
with one of its implicit breakpoints, causing the program to crash, as 
seen for example with the `mips-linux-gnu' target, o32 ABI, MIPS16 code, 
and the gdb.base/advance.exp test case:

(gdb) continue
Continuing.

Program received signal SIGBUS, Bus error.
_dl_debug_initialize (ldbase=0, ns=0) at dl-debug.c:51
51	    r = &_r_debug;
(gdb) FAIL: gdb.base/advance.exp: Can't run to main

	gdb/
	PR breakpoints/21886
	* mem-break.c (default_memory_insert_breakpoint): Use 
	`->placed_address' rather than `->reqstd_address' for the 
	breakpoint location.
---
On Fri, 4 Aug 2017, Yao Qi wrote:

> "Maciej W. Rozycki" <macro@imgtec.com> writes:
> 
> > Fix a commit cd6c3b4ffc4e ("New gdbarch methods breakpoint_kind_from_pc 
> > and sw_breakpoint_from_kind") regression and restore the use of 
> > ->placed_size rather than ->reqstd_address as the location for a memory 
> 
> s/placed_size/placed_address/

 Oh, I see you've noticed it too! :)

> The patch looks good to me, but please give me two or three days to run
> the tests on an armv7 board.  The board is being used for other tests,
> and I'll start the regression test on Monday next week.

 Sure.  Here's v2 with an updated description.  No changes to the patch 
itself.

  Maciej

Changes from v1:

- Description corrected, s/->placed_size/->placed_address/,

- Quotation made consistent across the description, e.g.
  `->reqstd_address' vs previous ->reqstd_address,

- PR annotation added.

---
 gdb/mem-break.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

gdb-mem-break-placed-address.diff
Index: binutils/gdb/mem-break.c
===================================================================
--- binutils.orig/gdb/mem-break.c	2017-07-30 22:45:34.000000000 +0100
+++ binutils/gdb/mem-break.c	2017-07-30 23:41:28.595612206 +0100
@@ -37,7 +37,7 @@ int
 default_memory_insert_breakpoint (struct gdbarch *gdbarch,
 				  struct bp_target_info *bp_tgt)
 {
-  CORE_ADDR addr = bp_tgt->reqstd_address;
+  CORE_ADDR addr = bp_tgt->placed_address;
   const unsigned char *bp;
   gdb_byte *readbuf;
   int bplen;