[RFA] ppc-linux-nat.c AltiVec regs ptrace

[Elena Zannoni <ezannoni at redhat dot com>]

This patch adds support for fetching and storing the AltiVec registers
on PPC.  I previously submitted a different patch based on a different
ptrace interface that was rejected by the ppc linux kernel maintainer.
A new ptrace interface has since been added to the kernel:
http://ppc.bkbits.net:8080/linuxppc_2_4/cset@1.543.1.14

This was the old patch, which is now obsolete:
http://sources.redhat.com/ml/gdb-patches/2001-11/msg00548.html


The Altivec registers are defined like this:
#define ELF_NVRREG      33      /* includes vscr */
/* Altivec registers */
typedef __vector128 elf_vrreg_t;
typedef elf_vrreg_t elf_vrregset_t[ELF_NVRREG];

There are 32 vector registers 16 bytes longs, plus a VSCR register
which is only 4 bytes long, but is fetched as a 16 bytes quantity. Up
to here we have the elf_vrregset_t structure.
Appended to this there is space for the VRSAVE register: 4 bytes.
Even though this vrsave register is not included in the regset
typedef, it is handled by the ptrace requests.

The layout is like this:

 |.|.|.|.|.....|.|.|.|.||.|.|.|x||.|
 <------->     <-------><-------><->
   VR0           VR31     VSCR    VRSAVE
(where x is the actual value of the vscr reg)


I have added a typedef to the ppc-linux-nat.c file to deal with
such a layout. I am not sure whether this is the best place to put
that. Maybe in gregset.h?


Elena


2002-02-19  Elena Zannoni  <ezannoni@redhat.com>

	* ppc-linux-nat.c (PTRACE_GETVRREGS, PTRACE_SETVRREGS): Define.
	(have_ptrace_getvrregs): Define for run time checks.
	(gdb_vrregset_t): New type for Altivec register handling.
	(fetch_register, store_register): Fetch/store altivec register
	when needed.
	(fetch_altivec_register, store_altivec-register): New functions.
	(supply_vrregset, fill_vrregset): New functions.
	(fetch_altivec_registers, store_altivec_registers): New functions.
	(fetch_ppc_registers, store_ppc_registers): Fetch/store altivec
	registers as well.

Index: ppc-linux-nat.c
===================================================================
RCS file: /cvs/uberbaum/gdb/ppc-linux-nat.c,v
retrieving revision 1.15
diff -u -p -r1.15 ppc-linux-nat.c
--- ppc-linux-nat.c	2002/02/18 15:08:40	1.15
+++ ppc-linux-nat.c	2002/02/20 19:27:29
@@ -17,7 +17,7 @@
    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place - Suite 330,
-   Boston, MA 02111-1307, USA.  */
+   Boston, MA 02111-1307, USA.*/
 
 #include "defs.h"
 #include "frame.h"
@@ -51,6 +51,39 @@
 #define PTRACE_XFER_TYPE int
 #endif
 
+/* This is necessary because of a glibc vs. kernel headers mess up.
+   Glibc's sys/ptrace.h defines PTRACE_GETFPXREGS and
+   PTRACE_SETFPXREGS to the same numbers that ppc's asm/ptrace.h
+   defines PTRACE_GETVRREGS and PTRACE_SETVRREGS to be. To complicate
+   matters further, the presence of such macros in glibc's ptrace.h
+   file doesn't guarantee that there is kernel support for
+   fetching/storing the AltiVec registers. So we have to fall back to
+   do a runtime check as well.  A similar trick is done for the
+   i386. */
+
+#ifdef HAVE_PTRACE_GETFPXREGS
+/* These definitions don't really have any functional impact, they are here 
+   to ease understanding of the ptrace calls. Glibc doesn't know about the
+   vrregs yet.*/
+#define PTRACE_GETVRREGS 18
+#define PTRACE_SETVRREGS 19
+
+/* This oddity is because the linux kernel defines elf_vrregset_t as
+   an array of 33 16 bytes long elements. I.e. it leaves out vrsave.
+   However the PTRACE_GETVRREGS and PTRACE_SETVRREGS requests return the
+   vrsave as an extra 4 bytes at the end. I opted for creating a flat
+   array of chars, so that it is easier to manipulate for gdb.  */
+#define SIZEOF_VRREGS 33*16+4
+typedef char gdb_vrregset_t[SIZEOF_VRREGS];
+#endif
+
+int have_ptrace_getvrregs
+#ifdef HAVE_PTRACE_GETFPXREGS
+     = 1;
+#else
+     = 0;
+#endif
+
 int
 kernel_u_size (void)
 {
@@ -109,6 +142,53 @@ ppc_ptrace_cannot_fetch_store_register (
   return (ppc_register_u_addr (regno) == -1);
 }
 
+#ifdef HAVE_PTRACE_GETFPXREGS
+/* The linux kernel ptrace interface for AltiVec registers uses the
+   registers set mechanism, as opposed to the interface for all the
+   other registers, that stores/fetches each register individually. */
+static void
+fetch_altivec_register (int tid, int regno)
+{
+  int ret;
+  int offset = 0;
+  gdb_vrregset_t regs;
+  struct gdbarch_tdep *tdep = gdbarch_tdep (current_gdbarch);
+  int vrregsize = REGISTER_RAW_SIZE (tdep->ppc_vr0_regnum);
+
+  ret = ptrace (PTRACE_GETVRREGS, tid, 0, &regs);
+  if (ret < 0)
+    {
+      if (errno == EIO)
+        {
+          have_ptrace_getvrregs = 0;
+          return;
+        }
+      perror_with_name ("Unable to fetch AltiVec register");
+    }
+ 
+  /* VSCR is fetched as a 16 bytes quantity, but it is really
+     4 bytes long on the hardware. We deal only with the lower
+     4 bytes of the vector. 
+     VRSAVE is at the end of the array in a 4 bytes slot, so there is no
+     need to define an offset for it. */
+  if (regno == (tdep->ppc_vrsave_regnum - 1))
+    offset = vrregsize - REGISTER_RAW_SIZE (tdep->ppc_vrsave_regnum);
+  
+  supply_register (regno,
+                   regs + (regno - tdep->ppc_vr0_regnum) * vrregsize + offset);
+}
+
+#else
+static void
+fetch_altivec_register (int tid, int regno)
+{
+  internal_error (__FILE__, __LINE__,
+		  "fetch_altivec_register: HAVE_PTRACE_GETFPXREGS not defined
+\nand have_ptrace_getvrregs set.");
+  return;
+}
+#endif /* HAVE_PTRACE_GETFPXREGS */
+
 static void
 fetch_register (int tid, int regno)
 {
@@ -119,6 +199,21 @@ fetch_register (int tid, int regno)
   char *buf = alloca (MAX_REGISTER_RAW_SIZE);
   CORE_ADDR regaddr = ppc_register_u_addr (regno);
 
+  if (altivec_register_p (regno))
+    {
+      /* If this is the first time through, or if it is not the first time
+         through, and we have comfirmed that there is kernel support for
+         such a ptrace request, then go and fetch the register. */
+      if (have_ptrace_getvrregs)
+       {
+         fetch_altivec_register (tid, regno);
+         return;
+       }
+     /* If we have discovered that there is no ptrace support for
+        AltiVec registers, fall through and return zeroes, because regaddr
+        will be -1 in this case. */
+    }
+
   if (regaddr == -1)
     {
       memset (buf, '\0', REGISTER_RAW_SIZE (regno));   /* Supply zeroes */
@@ -142,14 +237,70 @@ fetch_register (int tid, int regno)
   supply_register (regno, buf);
 }
 
+static void
+supply_vrregset (gdb_vrregset_t *vrregsetp)
+{
+  int i;
+  struct gdbarch_tdep *tdep = gdbarch_tdep (current_gdbarch);
+  int num_of_vrregs = tdep->ppc_vrsave_regnum - tdep->ppc_vr0_regnum;
+  int vrregsize = REGISTER_RAW_SIZE (tdep->ppc_vr0_regnum);
+  int offset = vrregsize - REGISTER_RAW_SIZE (tdep->ppc_vrsave_regnum);
+
+  for (i = 0; i < num_of_vrregs - 1; i++)
+    {
+      /* The last 2 registers of this set are only 32 bit long, not 128.
+         However an offset is necessary only for VSCR because it occupies 
+         a whole vector, while VRSAVE occupies a full 4 bytes slot. */
+      if (i == (tdep->ppc_vrsave_regnum - 1))
+        supply_register (tdep->ppc_vr0_regnum + i,
+                         *vrregsetp + i * vrregsize + offset);
+      else
+        supply_register (tdep->ppc_vr0_regnum + i, *vrregsetp + i * vrregsize);
+    }
+}
+
+#ifdef HAVE_PTRACE_GETFPXREGS
+
+static void
+fetch_altivec_registers (int tid)
+{
+  int ret;
+  gdb_vrregset_t regs;
+  
+  ret = ptrace (PTRACE_GETVRREGS, tid, 0, &regs);
+  if (ret < 0)
+    {
+      if (errno == EIO)
+	{
+          have_ptrace_getvrregs = 0;
+	  return;
+	}
+      perror_with_name ("Unable to fetch AltiVec registers");
+    }
+  supply_vrregset (&regs);
+}
+#else
+static void
+fetch_altivec_registers (int tid)
+{
+  internal_error (__FILE__, __LINE__,
+		  "fetch_altivec_registers: HAVE_PTRACE_GETFPXREGS not defined
+\nand have_ptrace_getvrregs set");
+  return;
+}
+#endif /* HAVE_PTRACE_GETFPXREGS */
+
 static void 
 fetch_ppc_registers (int tid)
 {
   int i;
-  int last_register = gdbarch_tdep (current_gdbarch)->ppc_mq_regnum;
-  
-  for (i = 0; i <= last_register; i++)
+  struct gdbarch_tdep *tdep = gdbarch_tdep (current_gdbarch);
+
+  for (i = 0; i <= tdep->ppc_mq_regnum; i++)
     fetch_register (tid, i);
+  if (have_ptrace_getvrregs)
+    if (tdep->ppc_vr0_regnum != -1 && tdep->ppc_vrsave_regnum != -1)
+      fetch_altivec_registers (tid);
 }
 
 /* Fetch registers from the child process.  Fetch all registers if
@@ -158,21 +309,65 @@ fetch_ppc_registers (int tid)
 void
 fetch_inferior_registers (int regno)
 {
- /* Overload thread id onto process id */
+  /* Overload thread id onto process id */
   int tid = TIDGET (inferior_ptid);
 
   /* No thread id, just use process id */
   if (tid == 0)
     tid = PIDGET (inferior_ptid);
 
-   if (regno == -1)
+  if (regno == -1)
     fetch_ppc_registers (tid);
   else 
     fetch_register (tid, regno);
 }
 
+#ifdef HAVE_PTRACE_GETFPXREGS
 /* Store one register. */
 static void
+store_altivec_register (int tid, int regno)
+{
+  int ret;
+  int offset = 0;
+  gdb_vrregset_t regs;
+  struct gdbarch_tdep *tdep = gdbarch_tdep (current_gdbarch);
+  int vrregsize = REGISTER_RAW_SIZE (tdep->ppc_vr0_regnum);
+
+  ret = ptrace (PTRACE_GETVRREGS, tid, 0, &regs);
+  if (ret < 0)
+    {
+      if (errno == EIO)
+        {
+          have_ptrace_getvrregs = 0;
+          return;
+        }
+      perror_with_name ("Unable to fetch AltiVec register");
+    }
+
+  /* VSCR is fetched as a 16 bytes quantity, but it is really
+     4 bytes long on the hardware. */
+  if (regno == (tdep->ppc_vrsave_regnum - 1))
+    offset = vrregsize - REGISTER_RAW_SIZE (tdep->ppc_vrsave_regnum);
+
+  regcache_collect (regno,
+                    regs + (regno - tdep->ppc_vr0_regnum) * vrregsize + offset);
+
+  ret = ptrace (PTRACE_SETVRREGS, tid, 0, &regs);
+  if (ret < 0)
+    perror_with_name ("Unable to store AltiVec register");
+}
+#else
+static void
+store_altivec_register (int tid)
+{
+  internal_error (__FILE__, __LINE__,
+		  "store_altivec_register: HAVE_PTRACE_GETFPXREGS not defined,
+\nand have_ptrace_getvrregs set");
+  return;
+}
+#endif
+
+static void
 store_register (int tid, int regno)
 {
   /* This isn't really an address.  But ptrace thinks of it as one.  */
@@ -182,11 +377,15 @@ store_register (int tid, int regno)
   unsigned int offset;         /* Offset of registers within the u area.  */
   char *buf = alloca (MAX_REGISTER_RAW_SIZE);
 
-  if (regaddr == -1)
+  if (altivec_register_p (regno))
     {
+      store_altivec_register (tid, regno);
       return;
     }
 
+  if (regaddr == -1)
+    return;
+
   regcache_collect (regno, buf);
   for (i = 0; i < REGISTER_RAW_SIZE (regno); i += sizeof (PTRACE_XFER_TYPE))
     {
@@ -204,13 +403,71 @@ store_register (int tid, int regno)
 }
 
 static void
+fill_vrregset (gdb_vrregset_t *vrregsetp)
+{
+  int i;
+  struct gdbarch_tdep *tdep = gdbarch_tdep (current_gdbarch);
+  int num_of_vrregs = tdep->ppc_vrsave_regnum - tdep->ppc_vr0_regnum;
+  int vrregsize = REGISTER_RAW_SIZE (tdep->ppc_vr0_regnum);
+  int offset = vrregsize - REGISTER_RAW_SIZE (tdep->ppc_vrsave_regnum);
+
+  for (i = 0; i < num_of_vrregs; i++)
+    {
+      /* The last 2 registers of this set are only 32 bit long, not 128.
+         Only VSCR is fetched as a 16 bytes quantity. */
+      if (i == (tdep->ppc_vrsave_regnum - 1))
+        regcache_collect (tdep->ppc_vr0_regnum + i,
+                          *vrregsetp + i * vrregsize + offset);
+      else
+        regcache_collect (tdep->ppc_vr0_regnum + i, *vrregsetp + i * vrregsize);
+    }
+}
+
+#ifdef HAVE_PTRACE_GETFPXREGS
+static void
+store_altivec_registers (int tid)
+{
+  int ret;
+  gdb_vrregset_t regs;
+
+  ret = ptrace (PTRACE_GETVRREGS, tid, 0, (int) &regs);
+  if (ret < 0)
+    {
+      if (errno == EIO)
+        {
+          have_ptrace_getvrregs = 0;
+          return;
+        }
+      perror_with_name ("Couldn't get AltiVec registers");
+    }
+
+  fill_vrregset (&regs);
+  
+  if (ptrace (PTRACE_SETVRREGS, tid, 0, (int) &regs) < 0)
+    perror_with_name ("Couldn't write AltiVec registers");
+}
+#else
+static void
+store_altivec_registers (int tid)
+{
+  internal_error (__FILE__, __LINE__,
+		  "store_altivec_registers: HAVE_PTRACE_GETFPXREGS not defined
+\nand have_ptrace_getvrregs set");
+  return;
+}
+#endif
+
+static void
 store_ppc_registers (int tid)
 {
   int i;
-  int last_register = gdbarch_tdep (current_gdbarch)->ppc_mq_regnum;
+  struct gdbarch_tdep *tdep = gdbarch_tdep (current_gdbarch);
   
-  for (i = 0; i <= last_register; i++)
+  for (i = 0; i <= tdep->ppc_mq_regnum; i++)
     store_register (tid, i);
+  if (have_ptrace_getvrregs)
+    if (tdep->ppc_vr0_regnum != -1 && tdep->ppc_vrsave_regnum != -1)
+      store_altivec_registers (tid);
 }
 
 void
@@ -281,6 +538,7 @@ void
 supply_fpregset (gdb_fpregset_t * fpregsetp)
 {
   int regi;
+
   for (regi = 0; regi < 32; regi++)
     supply_register (FP0_REGNUM + regi, (char *) (*fpregsetp + regi));
 }