[PowerPC] Fix access to VSCR in linux targets

The 4-byte VSCR register is found inside a 16-byte field in the regset
returned by ptrace and in core files. The position of VSCR depends on
the endianess of the target, which was previously assumed to be
big-endian for the purpose of getting VSCR. This patch removes this
assumption to fix access to VSCR in little-endian mode.

gdb/ChangeLog:
2018-05-22  Pedro Franco de Carvalho  <pedromfc@linux.vnet.ibm.com>

	* ppc-tdep.h (struct ppc_reg_offsets): Remove vector register
	offset fields.
	* ppc-fbsd-tdep.c (ppc32_fbsd_reg_offsets): Remove initializers
	for vector register offset fields.
	(ppc64_fbsd_reg_offsets): Likewise.
	* ppc-nbsd-tdep.c (_initialize_ppcnbsd_tdep): Remove assignment
	to vector register offset fields.
	* ppc-obsd-tdep.c (_initialize_ppcnbsd_tdep): Remove assignment
	to vector register offset fields.
	* ppc-obsd-nat.c (_initialize_ppcobsd_nat): Remove assignment to
	vector register offset fields.
	* rs6000-aix-tdep.c (rs6000_aix32_reg_offsets): Remove
	initializers for vector register offset fields.
	(rs6000_aix64_reg_offsets): Likewise.
	* rs6000-tdep.c (ppc_vrreg_offset): Remove.
	(ppc_supply_vrregset): Remove.
	(ppc_collect_vrregset): Remove.
	* ppc-linux-tdep.c (ppc_linux_collect_vrregset): New function.
	(ppc_linux_vrregset) : New function.
	(ppc32_le_linux_vrregmap, ppc32_be_linux_vrregmap)
	(ppc32_le_linux_vrregset, ppc32_be_linux_vrregset): New globals.
	(ppc32_linux_vrregset): Remove.
	(ppc_linux_iterate_over_regset_sections): Call ppc_linux_vrregset
	and use result instead of ppc32_linux_vrregset.
	(ppc32_linux_reg_offsets): Remove initializers for vector register
	offset fields.
	(ppc64_linux_reg_offsets): Likewise.
	* ppc-linux-tdep.h (ppc_linux_vrregset): New declaration.
	* ppc-linux-nat.c: Include regset.h.
	(gdb_vrregset_t): Adjust comment to account for little-endian
	mode.
	(supply_vrregset, fill_vrregset): Remove.
	(fetch_altivec_register, store_altivec_register): Remove.
	(fetch_altivec_registers): Add regno parameter. Get regset using
	ppc_linux_vrregset. Use regset to supply registers.
	(store_altivec_registers): Add regno parameter. Get regset using
	ppc_linux_vrregset. Use regset to collect registers.
	(fetch_register): Call fetch_altivec_registers instead of
	fetch_altivec_register.
	(store_register): Call store_altivec_registers instead of
	store_altivec_register.
	(fetch_ppc_registers): Call fetch_altivec_registers with -1 for
	the new regno parameter.
	(store_ppc_registers): Call store_altivec_registers with -1 for
	the new regno parameter.

gdb/gdbserver/ChangeLog:
2018-05-22  Pedro Franco de Carvalho  <pedromfc@linux.vnet.ibm.com>

	* linux-ppc-low.c (ppc_fill_vrregset): Add vscr_offset variable.
	Set vscr_offset to 0 in little-endian mode and 12 in big-endian
	mode. Call collect_register_by_name with vscr using
	vscr_offset. Zero-pad vscr and vrsave fields in collector buffer.
	(ppc_store_vrregset): Add and set vscr_offset variable as in
	ppc_fill_vrregset. Call supply_register_by_name with vscr using
	vscr_offset.

1 files changed, 64 insertions, 18 deletions

diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
index 344069d..7362c4b 100644
--- a/gdb/ppc-linux-tdep.c
+++ b/gdb/ppc-linux-tdep.c
@@ -444,6 +444,24 @@ ppc_linux_collect_gregset (const struct regset *regset,
     }
 }
 
+static void
+ppc_linux_collect_vrregset (const struct regset *regset,
+			    const struct regcache *regcache,
+			    int regnum, void *buf, size_t len)
+{
+  gdb_byte *vrregs = (gdb_byte *) buf;
+
+  /* Zero-pad the unused bytes in the fields for vscr and vrsave
+     in case they get displayed somewhere (e.g. in core files).  */
+  if (regnum == PPC_VSCR_REGNUM || regnum == -1)
+    memset (&vrregs[32 * 16], 0, 16);
+
+  if (regnum == PPC_VRSAVE_REGNUM || regnum == -1)
+    memset (&vrregs[33 * 16], 0, 16);
+
+  regcache_collect_regset (regset, regcache, regnum, buf, len);
+}
+
 /* Regset descriptions.  */
 static const struct ppc_reg_offsets ppc32_linux_reg_offsets =
   {
@@ -462,12 +480,7 @@ static const struct ppc_reg_offsets ppc32_linux_reg_offsets =
     /* Floating-point registers.  */
     /* .f0_offset = */ 0,
     /* .fpscr_offset = */ 256,
-    /* .fpscr_size = */ 8,
-
-    /* AltiVec registers.  */
-    /* .vr0_offset = */ 0,
-    /* .vscr_offset = */ 512 + 12,
-    /* .vrsave_offset = */ 528
+    /* .fpscr_size = */ 8
   };
 
 static const struct ppc_reg_offsets ppc64_linux_reg_offsets =
@@ -487,12 +500,7 @@ static const struct ppc_reg_offsets ppc64_linux_reg_offsets =
     /* Floating-point registers.  */
     /* .f0_offset = */ 0,
     /* .fpscr_offset = */ 256,
-    /* .fpscr_size = */ 8,
-
-    /* AltiVec registers.  */
-    /* .vr0_offset = */ 0,
-    /* .vscr_offset = */ 512 + 12,
-    /* .vrsave_offset = */ 528
+    /* .fpscr_size = */ 8
   };
 
 static const struct regset ppc32_linux_gregset = {
@@ -513,10 +521,36 @@ static const struct regset ppc32_linux_fpregset = {
   ppc_collect_fpregset
 };
 
-static const struct regset ppc32_linux_vrregset = {
-  &ppc32_linux_reg_offsets,
-  ppc_supply_vrregset,
-  ppc_collect_vrregset
+static const struct regcache_map_entry ppc32_le_linux_vrregmap[] =
+  {
+      { 32, PPC_VR0_REGNUM, 16 },
+      { 1, PPC_VSCR_REGNUM, 4 },
+      { 1, REGCACHE_MAP_SKIP, 12 },
+      { 1, PPC_VRSAVE_REGNUM, 4 },
+      { 1, REGCACHE_MAP_SKIP, 12 },
+      { 0 }
+  };
+
+static const struct regcache_map_entry ppc32_be_linux_vrregmap[] =
+  {
+      { 32, PPC_VR0_REGNUM, 16 },
+      { 1, REGCACHE_MAP_SKIP, 12},
+      { 1, PPC_VSCR_REGNUM, 4 },
+      { 1, PPC_VRSAVE_REGNUM, 4 },
+      { 1, REGCACHE_MAP_SKIP, 12 },
+      { 0 }
+  };
+
+static const struct regset ppc32_le_linux_vrregset = {
+  ppc32_le_linux_vrregmap,
+  regcache_supply_regset,
+  ppc_linux_collect_vrregset
+};
+
+static const struct regset ppc32_be_linux_vrregset = {
+  ppc32_be_linux_vrregmap,
+  regcache_supply_regset,
+  ppc_linux_collect_vrregset
 };
 
 static const struct regset ppc32_linux_vsxregset = {
@@ -537,6 +571,15 @@ ppc_linux_fpregset (void)
   return &ppc32_linux_fpregset;
 }
 
+const struct regset *
+ppc_linux_vrregset (struct gdbarch *gdbarch)
+{
+  if (gdbarch_byte_order (gdbarch) == BFD_ENDIAN_BIG)
+    return &ppc32_be_linux_vrregset;
+  else
+    return &ppc32_le_linux_vrregset;
+}
+
 /* Iterate over supported core file register note sections. */
 
 static void
@@ -557,8 +600,11 @@ ppc_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
   cb (".reg2", 264, &ppc32_linux_fpregset, NULL, cb_data);
 
   if (have_altivec)
-    cb (".reg-ppc-vmx", PPC_LINUX_SIZEOF_VRREGSET, &ppc32_linux_vrregset,
-	"ppc Altivec", cb_data);
+    {
+      const struct regset *vrregset = ppc_linux_vrregset (gdbarch);
+      cb (".reg-ppc-vmx", PPC_LINUX_SIZEOF_VRREGSET, vrregset,
+	  "ppc Altivec", cb_data);
+    }
 
   if (have_vsx)
     cb (".reg-ppc-vsx", PPC_LINUX_SIZEOF_VSXREGSET,