[PowerPC] Disable regsets using zero sizes in gdbserver

Currently the linux-ppc-low.c fill/store functions for extended
regsets check whether they should execute by using the global hwcap
variable.

This patch explicitly sets the regset sizes to zero when needed to
disable them instead, so that the fill/store functions are not called
in the first place by regsets_fetch_inferior_registers in linux-low.c.

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

	* linux-ppc-low.c (ppc_fill_vsxregset): Remove ppc_hwcap check.
	(ppc_store_vsxregset): Likewise.
	(ppc_fill_vrregset): Likewise.
	(ppc_store_vrregset): Likewise.
	(ppc_fill_evrregset): Likewise.
	(ppc_store_evrregset): Likewise.
	(ppc_regsets): Set VSX/VR/EVR regset sizes to 0.
	(ppc_arch_setup): Iterate through ppc_regsets and set sizes when
	needed.

2 files changed, 36 insertions, 21 deletions

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 7d8b704..9149c2f 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,5 +1,17 @@
 2018-05-22  Pedro Franco de Carvalho  <pedromfc@linux.vnet.ibm.com>
 
+	* linux-ppc-low.c (ppc_fill_vsxregset): Remove ppc_hwcap check.
+	(ppc_store_vsxregset): Likewise.
+	(ppc_fill_vrregset): Likewise.
+	(ppc_store_vrregset): Likewise.
+	(ppc_fill_evrregset): Likewise.
+	(ppc_store_evrregset): Likewise.
+	(ppc_regsets): Set VSX/VR/EVR regset sizes to 0.
+	(ppc_arch_setup): Iterate through ppc_regsets and set sizes when
+	needed.
+
+2018-05-22  Pedro Franco de Carvalho  <pedromfc@linux.vnet.ibm.com>
+
 	* linux-ppc-low.c (ppc_arch_setup): Remove code for getting the
 	wordsize of the inferior. Call ppc_linux_target_wordsize.
 
diff --git a/gdb/gdbserver/linux-ppc-low.c b/gdb/gdbserver/linux-ppc-low.c
index 30fcd41..b440b0e 100644
--- a/gdb/gdbserver/linux-ppc-low.c
+++ b/gdb/gdbserver/linux-ppc-low.c
@@ -467,9 +467,6 @@ ppc_fill_vsxregset (struct regcache *regcache, void *buf)
   int i, base;
   char *regset = (char *) buf;
 
-  if (!(ppc_hwcap & PPC_FEATURE_HAS_VSX))
-    return;
-
   base = find_regno (regcache->tdesc, "vs0h");
   for (i = 0; i < 32; i++)
     collect_register (regcache, base + i, &regset[i * 8]);
@@ -481,9 +478,6 @@ ppc_store_vsxregset (struct regcache *regcache, const void *buf)
   int i, base;
   const char *regset = (const char *) buf;
 
-  if (!(ppc_hwcap & PPC_FEATURE_HAS_VSX))
-    return;
-
   base = find_regno (regcache->tdesc, "vs0h");
   for (i = 0; i < 32; i++)
     supply_register (regcache, base + i, &regset[i * 8]);
@@ -497,9 +491,6 @@ ppc_fill_vrregset (struct regcache *regcache, void *buf)
   int i, base;
   char *regset = (char *) buf;
 
-  if (!(ppc_hwcap & PPC_FEATURE_HAS_ALTIVEC))
-    return;
-
   base = find_regno (regcache->tdesc, "vr0");
   for (i = 0; i < 32; i++)
     collect_register (regcache, base + i, &regset[i * 16]);
@@ -514,9 +505,6 @@ ppc_store_vrregset (struct regcache *regcache, const void *buf)
   int i, base;
   const char *regset = (const char *) buf;
 
-  if (!(ppc_hwcap & PPC_FEATURE_HAS_ALTIVEC))
-    return;
-
   base = find_regno (regcache->tdesc, "vr0");
   for (i = 0; i < 32; i++)
     supply_register (regcache, base + i, &regset[i * 16]);
@@ -538,9 +526,6 @@ ppc_fill_evrregset (struct regcache *regcache, void *buf)
   int i, ev0;
   struct gdb_evrregset_t *regset = (struct gdb_evrregset_t *) buf;
 
-  if (!(ppc_hwcap & PPC_FEATURE_HAS_SPE))
-    return;
-
   ev0 = find_regno (regcache->tdesc, "ev0h");
   for (i = 0; i < 32; i++)
     collect_register (regcache, ev0 + i, &regset->evr[i]);
@@ -555,9 +540,6 @@ ppc_store_evrregset (struct regcache *regcache, const void *buf)
   int i, ev0;
   const struct gdb_evrregset_t *regset = (const struct gdb_evrregset_t *) buf;
 
-  if (!(ppc_hwcap & PPC_FEATURE_HAS_SPE))
-    return;
-
   ev0 = find_regno (regcache->tdesc, "ev0h");
   for (i = 0; i < 32; i++)
     supply_register (regcache, ev0 + i, &regset->evr[i]);
@@ -579,11 +561,11 @@ static struct regset_info ppc_regsets[] = {
      fetch them every time, but still fall back to PTRACE_PEEKUSER for the
      general registers.  Some kernels support these, but not the newer
      PPC_PTRACE_GETREGS.  */
-  { PTRACE_GETVSXREGS, PTRACE_SETVSXREGS, 0, SIZEOF_VSXREGS, EXTENDED_REGS,
+  { PTRACE_GETVSXREGS, PTRACE_SETVSXREGS, 0, 0, EXTENDED_REGS,
   ppc_fill_vsxregset, ppc_store_vsxregset },
-  { PTRACE_GETVRREGS, PTRACE_SETVRREGS, 0, SIZEOF_VRREGS, EXTENDED_REGS,
+  { PTRACE_GETVRREGS, PTRACE_SETVRREGS, 0, 0, EXTENDED_REGS,
     ppc_fill_vrregset, ppc_store_vrregset },
-  { PTRACE_GETEVRREGS, PTRACE_SETEVRREGS, 0, 32 * 4 + 8 + 4, EXTENDED_REGS,
+  { PTRACE_GETEVRREGS, PTRACE_SETEVRREGS, 0, 0, EXTENDED_REGS,
     ppc_fill_evrregset, ppc_store_evrregset },
   { 0, 0, 0, 0, GENERAL_REGS, ppc_fill_gregset, NULL },
   NULL_REGSET
@@ -619,7 +601,9 @@ static void
 ppc_arch_setup (void)
 {
   const struct target_desc *tdesc;
+  struct regset_info *regset;
   struct ppc_linux_features features = ppc_linux_no_features;
+
   int tid = lwpid_of (current_thread);
 
   features.wordsize = ppc_linux_target_wordsize (tid);
@@ -671,6 +655,25 @@ ppc_arch_setup (void)
 #endif
 
   current_process ()->tdesc = tdesc;
+
+  for (regset = ppc_regsets; regset->size >= 0; regset++)
+    switch (regset->get_request)
+      {
+      case PTRACE_GETVRREGS:
+	regset->size = features.altivec ? SIZEOF_VRREGS : 0;
+	break;
+      case PTRACE_GETVSXREGS:
+	regset->size = features.vsx ? SIZEOF_VSXREGS : 0;
+	break;
+      case PTRACE_GETEVRREGS:
+	if (ppc_hwcap & PPC_FEATURE_HAS_SPE)
+	  regset->size = 32 * 4 + 8 + 4;
+	else
+	  regset->size = 0;
+	break;
+      default:
+	break;
+      }
 }
 
 /* Implementation of linux_target_ops method "supports_tracepoints".  */