Re: [PATCH] Enable hw watchpoint with longer ranges using DAWR on Power

[Edjunior Barbosa Machado <emachado@linux.vnet.ibm.com>]

On 07/02/2013 05:03 PM, Eli Zaretskii wrote:
> Is only one watchpoint of this kind possible at any given time?  If
> more than one such watchpoint can be used at the same time, I don't
> see why we should expose the 512-byte limitation to users.  Just use
> more than one such watchpoint to cover the range of addresses
> requested by the user command.

Yes, currently there is only one hw watchpoint available on Power servers. The
new feature just allows to watch longer ranges using this hw watchpoint, up to
512 bytes, instead of previous 8 bytes limit.

I'm resending the patch fixing the comment as Luis suggested. And I also hope
we can get the 'booke' renaming upstream soon :)

Thanks for the feedback.
--
Edjunior

gdb/ChangeLog
2013-07-02  Edjunior Barbosa Machado  <emachado@linux.vnet.ibm.com>

	* ppc-linux-nat.c (PPC_DEBUG_FEATURE_DATA_BP_DAWR): New define.
	(ppc_linux_region_ok_for_hw_watchpoint): Add checking to use the new
	DAWR interface for longer ranges hardware watchpoint (up to 512 bytes).

---
 gdb/ppc-linux-nat.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/gdb/ppc-linux-nat.c b/gdb/ppc-linux-nat.c
index 65d4f4a..ce437dd 100644
--- a/gdb/ppc-linux-nat.c
+++ b/gdb/ppc-linux-nat.c
@@ -177,7 +177,11 @@ struct ppc_hw_breakpoint
         (1<<((n)+PPC_BREAKPOINT_CONDITION_BE_SHIFT))
 #endif /* PPC_PTRACE_GETHWDBGINFO */
 
-
+/* Feature defined on Linux kernel v3.9: DAWR interface, that enables wider
+   watchpoint (up to 512 bytes).  */
+#ifndef PPC_DEBUG_FEATURE_DATA_BP_DAWR
+#define PPC_DEBUG_FEATURE_DATA_BP_DAWR	0x10
+#endif /* PPC_DEBUG_FEATURE_DATA_BP_DAWR */
 
 /* Similarly for the general-purpose (gp0 -- gp31)
    and floating-point registers (fp0 -- fp31).  */
@@ -1502,6 +1506,7 @@ ppc_linux_region_ok_for_hw_watchpoint (CORE_ADDR addr, int len)
      to determine the hardcoded watchable region for watchpoints.  */
   if (have_ptrace_booke_interface ())
     {
+      int region_size;
       /* Embedded DAC-based processors, like the PowerPC 440 have ranged
 	 watchpoints and can watch any access within an arbitrary memory
 	 region. This is useful to watch arrays and structs, for instance.  It
@@ -1510,11 +1515,17 @@ ppc_linux_region_ok_for_hw_watchpoint (CORE_ADDR addr, int len)
 	  && booke_debug_info.features & PPC_DEBUG_FEATURE_DATA_BP_RANGE
 	  && ppc_linux_get_hwcap () & PPC_FEATURE_BOOKE)
 	return 2;
+      /* Check if the processor provides DAWR interface.  */
+      if (booke_debug_info.features & PPC_DEBUG_FEATURE_DATA_BP_DAWR)
+	/* DAWR interface allows to watch up to 512 byte wide ranges which
+ 	   can't cross a 512 byte boundary.  */
+        region_size = 512;
+      else
+	region_size = booke_debug_info.data_bp_alignment;
       /* Server processors provide one hardware watchpoint and addr+len should
          fall in the watchable region provided by the ptrace interface.  */
-      if (booke_debug_info.data_bp_alignment
-	  && (addr + len > (addr & ~(booke_debug_info.data_bp_alignment - 1))
-	      + booke_debug_info.data_bp_alignment))
+      if (region_size
+	  && (addr + len > (addr & ~(region_size - 1)) + region_size))
 	return 0;
     }
   /* addr+len must fall in the 8 byte watchable region for DABR-based
-- 
1.8.2.1