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.

1 files changed, 54 insertions, 0 deletions

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;