Support fs_base and gs_base on FreeBSD/i386.

The i386 BSD native target uses the same ptrace operations
(PT_[GS]ET[FG]SBASE) as the amd64 BSD native target to fetch and store
the registers.

The amd64 BSD native now uses 'tdep->fsbase_regnum' instead of
hardcoding AMD64_FSBASE_REGNUM and AMD64_GSBASE_REGNUM to support
32-bit targets.  In addition, the store operations explicitly zero the
new register value before fetching it from the register cache to
ensure 32-bit values are zero-extended.

gdb/ChangeLog:

	* amd64-bsd-nat.c (amd64bsd_fetch_inferior_registers): Use
	tdep->fsbase_regnum instead of constants for fs_base and gs_base.
	(amd64bsd_store_inferior_registers): Likewise.
	* amd64-fbsd-nat.c (amd64_fbsd_nat_target::read_description):
	Enable segment base registers.
	* i386-bsd-nat.c (i386bsd_fetch_inferior_registers): Use
	PT_GETFSBASE and PT_GETGSBASE.
	(i386bsd_store_inferior_registers): Use PT_SETFSBASE and
	PT_SETGSBASE.
	* i386-fbsd-nat.c (i386_fbsd_nat_target::read_description): Enable
	segment base registers.
	* i386-fbsd-tdep.c (i386fbsd_core_read_description): Likewise.

6 files changed, 91 insertions, 12 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 79ba941..c91e975 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,20 @@
 2019-03-12  John Baldwin  <jhb@FreeBSD.org>
 
+	* amd64-bsd-nat.c (amd64bsd_fetch_inferior_registers): Use
+	tdep->fsbase_regnum instead of constants for fs_base and gs_base.
+	(amd64bsd_store_inferior_registers): Likewise.
+	* amd64-fbsd-nat.c (amd64_fbsd_nat_target::read_description):
+	Enable segment base registers.
+	* i386-bsd-nat.c (i386bsd_fetch_inferior_registers): Use
+	PT_GETFSBASE and PT_GETGSBASE.
+	(i386bsd_store_inferior_registers): Use PT_SETFSBASE and
+	PT_SETGSBASE.
+	* i386-fbsd-nat.c (i386_fbsd_nat_target::read_description): Enable
+	segment base registers.
+	* i386-fbsd-tdep.c (i386fbsd_core_read_description): Likewise.
+
+2019-03-12  John Baldwin  <jhb@FreeBSD.org>
+
 	* amd64-fbsd-nat.c (amd64_fbsd_nat_target::read_description):
 	Update calls to i386_target_description to add 'segments'
 	parameter.
diff --git a/gdb/amd64-bsd-nat.c b/gdb/amd64-bsd-nat.c
index a2a91ab..35763a5 100644
--- a/gdb/amd64-bsd-nat.c
+++ b/gdb/amd64-bsd-nat.c
@@ -43,6 +43,9 @@ amd64bsd_fetch_inferior_registers (struct regcache *regcache, int regnum)
 {
   struct gdbarch *gdbarch = regcache->arch ();
   pid_t pid = get_ptrace_pid (regcache->ptid ());
+#if defined(PT_GETFSBASE) || defined(PT_GETGSBASE)
+  const struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
+#endif
 
   if (regnum == -1 || amd64_native_gregset_supplies_p (gdbarch, regnum))
     {
@@ -57,27 +60,27 @@ amd64bsd_fetch_inferior_registers (struct regcache *regcache, int regnum)
     }
 
 #ifdef PT_GETFSBASE
-  if (regnum == -1 || regnum == AMD64_FSBASE_REGNUM)
+  if (regnum == -1 || regnum == tdep->fsbase_regnum)
     {
       register_t base;
 
       if (ptrace (PT_GETFSBASE, pid, (PTRACE_TYPE_ARG3) &base, 0) == -1)
 	perror_with_name (_("Couldn't get segment register fs_base"));
 
-      regcache->raw_supply (AMD64_FSBASE_REGNUM, &base);
+      regcache->raw_supply (tdep->fsbase_regnum, &base);
       if (regnum != -1)
 	return;
     }
 #endif
 #ifdef PT_GETGSBASE
-  if (regnum == -1 || regnum == AMD64_GSBASE_REGNUM)
+  if (regnum == -1 || regnum == tdep->fsbase_regnum + 1)
     {
       register_t base;
 
       if (ptrace (PT_GETGSBASE, pid, (PTRACE_TYPE_ARG3) &base, 0) == -1)
 	perror_with_name (_("Couldn't get segment register gs_base"));
 
-      regcache->raw_supply (AMD64_GSBASE_REGNUM, &base);
+      regcache->raw_supply (tdep->fsbase_regnum + 1, &base);
       if (regnum != -1)
 	return;
     }
@@ -116,6 +119,9 @@ amd64bsd_store_inferior_registers (struct regcache *regcache, int regnum)
 {
   struct gdbarch *gdbarch = regcache->arch ();
   pid_t pid = get_ptrace_pid (regcache->ptid ());
+#if defined(PT_SETFSBASE) || defined(PT_SETGSBASE)
+  const struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
+#endif
 
   if (regnum == -1 || amd64_native_gregset_supplies_p (gdbarch, regnum))
     {
@@ -134,11 +140,13 @@ amd64bsd_store_inferior_registers (struct regcache *regcache, int regnum)
     }
 
 #ifdef PT_SETFSBASE
-  if (regnum == -1 || regnum == AMD64_FSBASE_REGNUM)
+  if (regnum == -1 || regnum == tdep->fsbase_regnum)
     {
       register_t base;
 
-      regcache->raw_collect (AMD64_FSBASE_REGNUM, &base);
+      /* Clear the full base value to support 32-bit targets.  */
+      base = 0;
+      regcache->raw_collect (tdep->fsbase_regnum, &base);
 
       if (ptrace (PT_SETFSBASE, pid, (PTRACE_TYPE_ARG3) &base, 0) == -1)
 	perror_with_name (_("Couldn't write segment register fs_base"));
@@ -147,11 +155,13 @@ amd64bsd_store_inferior_registers (struct regcache *regcache, int regnum)
     }
 #endif
 #ifdef PT_SETGSBASE
-  if (regnum == -1 || regnum == AMD64_GSBASE_REGNUM)
+  if (regnum == -1 || regnum == tdep->fsbase_regnum + 1)
     {
       register_t base;
 
-      regcache->raw_collect (AMD64_GSBASE_REGNUM, &base);
+      /* Clear the full base value to support 32-bit targets.  */
+      base = 0;
+      regcache->raw_collect (tdep->fsbase_regnum + 1, &base);
 
       if (ptrace (PT_SETGSBASE, pid, (PTRACE_TYPE_ARG3) &base, 0) == -1)
 	perror_with_name (_("Couldn't write segment register gs_base"));
diff --git a/gdb/amd64-fbsd-nat.c b/gdb/amd64-fbsd-nat.c
index 9fff763..cc676d3 100644
--- a/gdb/amd64-fbsd-nat.c
+++ b/gdb/amd64-fbsd-nat.c
@@ -190,13 +190,13 @@ amd64_fbsd_nat_target::read_description ()
       if (is64)
 	return amd64_target_description (xcr0, true);
       else
-	return i386_target_description (xcr0, false);
+	return i386_target_description (xcr0, true);
     }
 #endif
   if (is64)
     return amd64_target_description (X86_XSTATE_SSE_MASK, true);
   else
-    return i386_target_description (X86_XSTATE_SSE_MASK, false);
+    return i386_target_description (X86_XSTATE_SSE_MASK, true);
 }
 
 #if defined(HAVE_PT_GETDBREGS) && defined(USE_SIGTRAP_SIGINFO)
diff --git a/gdb/i386-bsd-nat.c b/gdb/i386-bsd-nat.c
index 009a8dc..a10b496 100644
--- a/gdb/i386-bsd-nat.c
+++ b/gdb/i386-bsd-nat.c
@@ -144,6 +144,33 @@ i386bsd_fetch_inferior_registers (struct regcache *regcache, int regnum)
 	return;
     }
 
+#ifdef PT_GETFSBASE
+  if (regnum == -1 || regnum == I386_FSBASE_REGNUM)
+    {
+      register_t base;
+
+      if (ptrace (PT_GETFSBASE, pid, (PTRACE_TYPE_ARG3) &base, 0) == -1)
+	perror_with_name (_("Couldn't get segment register fs_base"));
+
+      regcache->raw_supply (I386_FSBASE_REGNUM, &base);
+      if (regnum != -1)
+	return;
+    }
+#endif
+#ifdef PT_GETGSBASE
+  if (regnum == -1 || regnum == I386_GSBASE_REGNUM)
+    {
+      register_t base;
+
+      if (ptrace (PT_GETGSBASE, pid, (PTRACE_TYPE_ARG3) &base, 0) == -1)
+	perror_with_name (_("Couldn't get segment register gs_base"));
+
+      regcache->raw_supply (I386_GSBASE_REGNUM, &base);
+      if (regnum != -1)
+	return;
+    }
+#endif
+
   if (regnum == -1 || regnum >= I386_ST0_REGNUM)
     {
       struct fpreg fpregs;
@@ -211,6 +238,33 @@ i386bsd_store_inferior_registers (struct regcache *regcache, int regnum)
 	return;
     }
 
+#ifdef PT_SETFSBASE
+  if (regnum == -1 || regnum == I386_FSBASE_REGNUM)
+    {
+      register_t base;
+
+      regcache->raw_collect (I386_FSBASE_REGNUM, &base);
+
+      if (ptrace (PT_SETFSBASE, pid, (PTRACE_TYPE_ARG3) &base, 0) == -1)
+	perror_with_name (_("Couldn't write segment register fs_base"));
+      if (regnum != -1)
+	return;
+    }
+#endif
+#ifdef PT_SETGSBASE
+  if (regnum == -1 || regnum == I386_GSBASE_REGNUM)
+    {
+      register_t base;
+
+      regcache->raw_collect (I386_GSBASE_REGNUM, &base);
+
+      if (ptrace (PT_SETGSBASE, pid, (PTRACE_TYPE_ARG3) &base, 0) == -1)
+	perror_with_name (_("Couldn't write segment register gs_base"));
+      if (regnum != -1)
+	return;
+    }
+#endif
+
   if (regnum == -1 || regnum >= I386_ST0_REGNUM)
     {
       struct fpreg fpregs;
diff --git a/gdb/i386-fbsd-nat.c b/gdb/i386-fbsd-nat.c
index 7106e90..be5d4c6 100644
--- a/gdb/i386-fbsd-nat.c
+++ b/gdb/i386-fbsd-nat.c
@@ -160,7 +160,7 @@ i386_fbsd_nat_target::read_description ()
   if (x86bsd_xsave_len == 0)
     xcr0 = X86_XSTATE_SSE_MASK;
 
-  return i386_target_description (xcr0, false);
+  return i386_target_description (xcr0, true);
 }
 #endif
 
diff --git a/gdb/i386-fbsd-tdep.c b/gdb/i386-fbsd-tdep.c
index 2f28bad..ac57e73 100644
--- a/gdb/i386-fbsd-tdep.c
+++ b/gdb/i386-fbsd-tdep.c
@@ -267,7 +267,7 @@ i386fbsd_core_read_description (struct gdbarch *gdbarch,
 				struct target_ops *target,
 				bfd *abfd)
 {
-  return i386_target_description (i386fbsd_core_read_xcr0 (abfd), false);
+  return i386_target_description (i386fbsd_core_read_xcr0 (abfd), true);
 }
 
 /* Similar to i386_supply_fpregset, but use XSAVE extended state.  */