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Re: [PATCH] mem-break: Fix breakpoint insertion location


On 2017-08-01 18:36, Maciej W. Rozycki wrote:
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
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_size 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/
	* mem-break.c (default_memory_insert_breakpoint): Use
	`->placed_address' rather than `->reqstd_address' for the
	breakpoint location.
---
Hi,

No regressions between plain commit cd6c3b4ffc4e^ and commit cd6c3b4ffc4e with this change applied in `mips-linux-gnu', o32, MIPS16 testing. This
brings that configuration back to sanity.

 OK for master and (as a grave regression) for 8.0?

  Maciej

---
 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;

IIUC, we end up writing the good breakpoint kind, but at the wrong address? For example, if the requested address is 0x1001, it means that there should be a micro/compressed MIPS breakpoint at address 0x1000, but that bug caused the breakpoint to be written at address 0x1001 instead. Is that right?

If so, I think the patch makes sense, I think Yao should have the final say.

Thanks,

Simon


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