[PATCH 2/2] Support the fs_base and gs_base registers on FreeBSD/amd64 native processes.

[John Baldwin <jhb@FreeBSD.org>]

Use ptrace operations to fetch and store the fs_base and gs_base registers
for FreeBSD/amd64 processes.  Note that FreeBSD does not currently store the
value of these registers in core dumps, so these registers are only
available when inspecting a running process.

gdb/ChangeLog:

	* amd64-bsd-nat.c (amd64bsd_fetch_inferior_registers): Use
	PT_GETFSBASE and PT_GETGSBASE.
	(amd64bsd_store_inferior_registers): Use PT_SETFSBASE and
	PT_SETGSBASE.
---
 gdb/ChangeLog       |  7 +++++++
 gdb/amd64-bsd-nat.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 2196419fa3..09fe66a49a 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,12 @@
 2017-06-26  John Baldwin  <jhb@FreeBSD.org>
 
+	* amd64-bsd-nat.c (amd64bsd_fetch_inferior_registers): Use
+	PT_GETFSBASE and PT_GETGSBASE.
+	(amd64bsd_store_inferior_registers): Use PT_SETFSBASE and
+	PT_SETGSBASE.
+
+2017-06-26  John Baldwin  <jhb@FreeBSD.org>
+
 	* features/Makefile (amd64.dat, amd64-avx.dat, amd64-mpx.dat)
 	(amd64-avx-mpx.dat, amd64-avx-avx512.dat)
 	(amd64-avx-mpx-avx512-pku.dat): Add i386/64bit-segments.xml in
diff --git a/gdb/amd64-bsd-nat.c b/gdb/amd64-bsd-nat.c
index ca61a3551b..41dee84269 100644
--- a/gdb/amd64-bsd-nat.c
+++ b/gdb/amd64-bsd-nat.c
@@ -57,6 +57,33 @@ amd64bsd_fetch_inferior_registers (struct target_ops *ops,
 	return;
     }
 
+#ifdef PT_GETFSBASE
+  if (regnum == -1 || regnum == AMD64_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 (regcache, AMD64_FSBASE_REGNUM, &base);
+      if (regnum != -1)
+	return;
+    }
+#endif
+#ifdef PT_GETGSBASE
+  if (regnum == -1 || regnum == AMD64_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 (regcache, AMD64_GSBASE_REGNUM, &base);
+      if (regnum != -1)
+	return;
+    }
+#endif
+
   if (regnum == -1 || !amd64_native_gregset_supplies_p (gdbarch, regnum))
     {
       struct fpreg fpregs;
@@ -108,6 +135,33 @@ amd64bsd_store_inferior_registers (struct target_ops *ops,
 	return;
     }
 
+#ifdef PT_SETFSBASE
+  if (regnum == -1 || regnum == AMD64_FSBASE_REGNUM)
+    {
+      register_t base;
+
+      regcache_raw_collect (regcache, AMD64_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 == AMD64_GSBASE_REGNUM)
+    {
+      register_t base;
+
+      regcache_raw_collect (regcache, AMD64_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 || !amd64_native_gregset_supplies_p (gdbarch, regnum))
     {
       struct fpreg fpregs;
-- 
2.11.0