[PATCH] IA64: $fr0==0.0, $fr1==1.0

[Pedro Alves <palves@redhat.com>]

> I see that $f0 (always 0.0) and $f1 (always 1.0) could/should be given
> similar treatment:
>
> (gdb) info register $f0 $f1
> f0             *value not available*
> f1             *value not available*
>

(...)

> gcore.exp failures related to these issues.

(because when debugging a live process "info registers" shows 'value
not available', but when debugging a core, "info registers" shows 0.0
for those registers.

(I was lazy and got the raw bytes of 1.0 by using "info float" after
writing 1 to $fp2...)

With yours, and these patches applied, gcore.exp passes cleanly
on ia64-unknown-linux-gnu.  Before, we had:

Running ../../../src/gdb/testsuite/gdb.base/gcore.exp ...
FAIL: gdb.base/gcore.exp: corefile restored general registers
FAIL: gdb.base/gcore.exp: corefile restored all registers

No regressions.  WDYT?

2012-03-28  Pedro Alves  <palves@redhat.com>

	* ia64-linux-nat.c (supply_fpregset, ia64_linux_fetch_register):
	Always supply $fr0 as 0.0 and $fr1 as 1.0.
---
 gdb/ia64-linux-nat.c |   35 ++++++++++++++++++++++++++++++++++-
 1 files changed, 34 insertions(+), 1 deletions(-)

diff --git a/gdb/ia64-linux-nat.c b/gdb/ia64-linux-nat.c
index 24bde2d..237f2c7 100644
--- a/gdb/ia64-linux-nat.c
+++ b/gdb/ia64-linux-nat.c
@@ -447,8 +447,20 @@ supply_fpregset (struct regcache *regcache, const fpregset_t *fpregsetp)
 {
   int regi;
   const char *from;
+  const gdb_byte f_zero[16] = { 0 };
+  const gdb_byte f_one[16] =
+    { 0, 0, 0, 0, 0, 0, 0, 0x80, 0xff, 0xff, 0, 0, 0, 0, 0, 0 };
 
-  for (regi = IA64_FR0_REGNUM; regi <= IA64_FR127_REGNUM; regi++)
+  /* Kernel generated cores have fr1==0 instead of 1.0.  Older GDBs
+     did the same.  So ignore whatever might be recorded in fpregset_t
+     for fr0/fr1 and always supply their expected values.  */
+
+  /* fr0 is always read as zero.  */
+  regcache_raw_supply (regcache, IA64_FR0_REGNUM, f_zero);
+  /* fr1 is always read as one (1.0).  */
+  regcache_raw_supply (regcache, IA64_FR1_REGNUM, f_one);
+
+  for (regi = IA64_FR2_REGNUM; regi <= IA64_FR127_REGNUM; regi++)
     {
       from = (const char *) &((*fpregsetp)[regi - IA64_FR0_REGNUM]);
       regcache_raw_supply (regcache, regi, from);
@@ -690,6 +702,27 @@ ia64_linux_fetch_register (struct regcache *regcache, int regnum)
       return;
     }
 
+  /* fr0 cannot be fetched but is always zero.  */
+  if (regnum == IA64_FR0_REGNUM)
+    {
+      const gdb_byte f_zero[16] = { 0 };
+
+      gdb_assert (sizeof (f_zero) == register_size (gdbarch, regnum));
+      regcache_raw_supply (regcache, regnum, f_zero);
+      return;
+    }
+
+  /* fr1 cannot be fetched but is always one (1.0).  */
+  if (regnum == IA64_FR1_REGNUM)
+    {
+      const gdb_byte f_one[16] =
+	{ 0, 0, 0, 0, 0, 0, 0, 0x80, 0xff, 0xff, 0, 0, 0, 0, 0, 0 };
+
+      gdb_assert (sizeof (f_one) == register_size (gdbarch, regnum));
+      regcache_raw_supply (regcache, regnum, f_one);
+      return;
+    }
+
   if (ia64_cannot_fetch_register (gdbarch, regnum))
     {
       regcache_raw_supply (regcache, regnum, NULL);