[PATCH 4/5] FreeBSD/x86: Read segment base registers from NT_X86_SEGBASES.

[John Baldwin <jhb@FreeBSD.org>]

FreeBSD kernels recently grew a new register core dump note containing
the base addresses of the %fs and %gs segments (corresponding to the
%fsbase and %gsbase registers).  Parse this note to permit inspecting
TLS variables in core dumps.  Native processes already supported TLS
via older ptrace() operations.
---
 gdb/amd64-fbsd-tdep.c | 18 ++++++++++++++++++
 gdb/i386-fbsd-tdep.c  | 18 ++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/gdb/amd64-fbsd-tdep.c b/gdb/amd64-fbsd-tdep.c
index da5c297902d..55764beaad2 100644
--- a/gdb/amd64-fbsd-tdep.c
+++ b/gdb/amd64-fbsd-tdep.c
@@ -37,6 +37,9 @@
    16-bit segment registers.  */
 #define AMD64_FBSD_SIZEOF_GREGSET	(22 * 8)
 
+/* The segment base register set consists of 2 64-bit registers.  */
+#define AMD64_FBSD_SIZEOF_SEGBASES_REGSET	(2 * 8)
+
 /* Register maps.  */
 
 static const struct regcache_map_entry amd64_fbsd_gregmap[] =
@@ -70,6 +73,13 @@ static const struct regcache_map_entry amd64_fbsd_gregmap[] =
   { 0 }
 };
 
+static const struct regcache_map_entry amd64_fbsd_segbases_regmap[] =
+{
+  { 1, AMD64_FSBASE_REGNUM, 0 },
+  { 1, AMD64_GSBASE_REGNUM, 0 },
+  { 0 }
+};
+
 /* This layout including fsbase and gsbase was adopted in FreeBSD
    8.0.  */
 
@@ -120,6 +130,11 @@ const struct regset amd64_fbsd_gregset =
   amd64_fbsd_gregmap, regcache_supply_regset, regcache_collect_regset
 };
 
+const struct regset amd64_fbsd_segbases_regset =
+{
+  amd64_fbsd_segbases_regmap, regcache_supply_regset, regcache_collect_regset
+};
+
 /* Support for signal handlers.  */
 
 /* In a signal frame, rsp points to a 'struct sigframe' which is
@@ -253,6 +268,9 @@ amd64fbsd_iterate_over_regset_sections (struct gdbarch *gdbarch,
       &amd64_fbsd_gregset, NULL, cb_data);
   cb (".reg2", tdep->sizeof_fpregset, tdep->sizeof_fpregset, &amd64_fpregset,
       NULL, cb_data);
+  cb (".reg-x86-segbases", AMD64_FBSD_SIZEOF_SEGBASES_REGSET,
+      AMD64_FBSD_SIZEOF_SEGBASES_REGSET, &amd64_fbsd_segbases_regset,
+      "segment bases", cb_data);
   cb (".reg-xstate", X86_XSTATE_SIZE (tdep->xcr0), X86_XSTATE_SIZE (tdep->xcr0),
       &amd64fbsd_xstateregset, "XSAVE extended state", cb_data);
 }
diff --git a/gdb/i386-fbsd-tdep.c b/gdb/i386-fbsd-tdep.c
index 16ffd576323..fad091f8472 100644
--- a/gdb/i386-fbsd-tdep.c
+++ b/gdb/i386-fbsd-tdep.c
@@ -35,6 +35,9 @@
 /* The general-purpose regset consists of 19 32-bit slots.  */
 #define I386_FBSD_SIZEOF_GREGSET	(19 * 4)
 
+/* The segment base register set consists of 2 32-bit registers.  */
+#define I386_FBSD_SIZEOF_SEGBASES_REGSET	(2 * 4)
+
 /* Register maps.  */
 
 static const struct regcache_map_entry i386_fbsd_gregmap[] =
@@ -61,6 +64,13 @@ static const struct regcache_map_entry i386_fbsd_gregmap[] =
   { 0 }
 };
 
+static const struct regcache_map_entry i386_fbsd_segbases_regmap[] =
+{
+  { 1, I386_FSBASE_REGNUM, 0 },
+  { 1, I386_GSBASE_REGNUM, 0 },
+  { 0 }
+};
+
 /* This layout including fsbase and gsbase was adopted in FreeBSD
    8.0.  */
 
@@ -103,6 +113,11 @@ const struct regset i386_fbsd_gregset =
   i386_fbsd_gregmap, regcache_supply_regset, regcache_collect_regset
 };
 
+const struct regset i386_fbsd_segbases_regset =
+{
+  i386_fbsd_segbases_regmap, regcache_supply_regset, regcache_collect_regset
+};
+
 /* Support for signal handlers.  */
 
 /* In a signal frame, esp points to a 'struct sigframe' which is
@@ -316,6 +331,9 @@ i386fbsd_iterate_over_regset_sections (struct gdbarch *gdbarch,
       &i386_fbsd_gregset, NULL, cb_data);
   cb (".reg2", tdep->sizeof_fpregset, tdep->sizeof_fpregset, &i386_fpregset,
       NULL, cb_data);
+  cb (".reg-x86-segbases", I386_FBSD_SIZEOF_SEGBASES_REGSET,
+      I386_FBSD_SIZEOF_SEGBASES_REGSET, &i386_fbsd_segbases_regset,
+      "segment bases", cb_data);
 
   if (tdep->xcr0 & X86_XSTATE_AVX)
     cb (".reg-xstate", X86_XSTATE_SIZE (tdep->xcr0),
-- 
2.34.1