$zero on alpha should always be available

[Pedro Alves <pedro at codesourcery dot com>]

On Sunday 22 May 2011 12:17:12, Pedro Alves wrote:
> On Saturday 21 May 2011 20:19:49, Mark Kettenis wrote:
> > Many RISC CPUs have a register that's hardwired to 0.  Typically GDB
> > code uses regcache_raw_supply(..., ..., NULL) to "transfer" the value
> > of such a register.  However these days, that marks the register as
> > unavailable.  This diff fixes that for %g0 on SPARC.
> > 
> > Committed as obvious.
> 
> Thanks!  The <unavailable> stuff is going into 7.3 as well.  Want
> to put the patch there too?
> 
> (I see alpha-tdep.c needs the same treatment for ALPHA_ZERO_REGNUM.)

Here's what I came up with by inspection.  I have no alpha machine to test
this on.  The alpha-nat.c change would need
checking on an alpha running OSF if we wanted to test this...


Pedro Alves

2011-05-23  Pedro Alves  <pedro@codesourcery.com>

	gdb/
	* alpha-tdep.c (alpha_cannot_fetch_register): Don't return true
	for ALPHA_ZERO_REGNUM.
	(alpha_supply_int_regs): Explicitly supply zero as the value for
	ALPHA_ZERO_REGNUM in the register cache.
	* alpha-nat.c (fetch_osf_core_registers): Ditto.

---
 gdb/alpha-nat.c  |    9 +++++++++
 gdb/alpha-tdep.c |    9 ++++++---
 2 files changed, 15 insertions(+), 3 deletions(-)

Index: src/gdb/alpha-tdep.c
===================================================================
--- src.orig/gdb/alpha-tdep.c	2011-04-20 16:22:32.000000000 +0100
+++ src/gdb/alpha-tdep.c	2011-05-23 18:24:29.448753681 +0100
@@ -111,8 +111,7 @@ alpha_register_name (struct gdbarch *gdb
 static int
 alpha_cannot_fetch_register (struct gdbarch *gdbarch, int regno)
 {
-  return (regno == ALPHA_ZERO_REGNUM
-          || strlen (alpha_register_name (gdbarch, regno)) == 0);
+  return (strlen (alpha_register_name (gdbarch, regno)) == 0);
 }
 
 static int
@@ -1424,7 +1423,11 @@ alpha_supply_int_regs (struct regcache *
       regcache_raw_supply (regcache, i, regs + i * 8);
 
   if (regno == ALPHA_ZERO_REGNUM || regno == -1)
-    regcache_raw_supply (regcache, ALPHA_ZERO_REGNUM, NULL);
+    {
+      const gdb_byte zero[8] = { 0 };
+
+      regcache_raw_supply (regcache, ALPHA_ZERO_REGNUM, zero);
+    }
 
   if (regno == ALPHA_PC_REGNUM || regno == -1)
     regcache_raw_supply (regcache, ALPHA_PC_REGNUM, pc);
Index: src/gdb/alpha-nat.c
===================================================================
--- src.orig/gdb/alpha-nat.c	2011-01-13 15:07:16.000000000 +0000
+++ src/gdb/alpha-nat.c	2011-05-23 18:28:14.428753680 +0100
@@ -101,6 +101,15 @@ fetch_osf_core_registers (struct regcach
 	  regcache_raw_supply (regcache, regno, NULL);
 	  continue;
 	}
+
+      if (regno == ALPHA_ZERO_REGNUM)
+	{
+	  const gdb_byte zero[8] = { 0 };
+
+	  regcache_raw_supply (regcache, regno, zero);
+	  continue;
+	}
+
       addr = 8 * core_reg_mapping[regno];
       if (addr < 0 || addr >= core_reg_size)
 	{