[RFC PATCH v2 3/5] Update x86 FreeBSD architectures to support XSAVE layouts.

[John Baldwin <jhb@FreeBSD.org>]

Add an implementation of gdbarch_core_xfer_x86_xsave_layout which uses
the size of an existing NT_X86_XSTATE core dump to determine the
offsets via i387_set_xsave_layout.

Use tdep->xsave_layout.sizeof_xsave as the size of the XSTATE register
set and only fetch/store the register set if this size is non-zero.
---
 gdb/amd64-fbsd-tdep.c |  8 ++++++--
 gdb/i386-fbsd-tdep.c  | 37 ++++++++++++++++++++++++++++++++++---
 gdb/i386-fbsd-tdep.h  |  6 ++++++
 3 files changed, 46 insertions(+), 5 deletions(-)

diff --git a/gdb/amd64-fbsd-tdep.c b/gdb/amd64-fbsd-tdep.c
index da5c297902d..37d89c98bc9 100644
--- a/gdb/amd64-fbsd-tdep.c
+++ b/gdb/amd64-fbsd-tdep.c
@@ -253,8 +253,10 @@ 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-xstate", X86_XSTATE_SIZE (tdep->xcr0), X86_XSTATE_SIZE (tdep->xcr0),
-      &amd64fbsd_xstateregset, "XSAVE extended state", cb_data);
+  if (tdep->xsave_layout.sizeof_xsave != 0)
+    cb (".reg-xstate", tdep->xsave_layout.sizeof_xsave,
+	tdep->xsave_layout.sizeof_xsave, &amd64fbsd_xstateregset,
+	"XSAVE extended state", cb_data);
 }
 
 /* Implement the get_thread_local_address gdbarch method.  */
@@ -295,6 +297,8 @@ amd64fbsd_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
   tramp_frame_prepend_unwinder (gdbarch, &amd64_fbsd_sigframe);
 
   tdep->xsave_xcr0_offset = I386_FBSD_XSAVE_XCR0_OFFSET;
+  set_gdbarch_core_xfer_x86_xsave_layout
+    (gdbarch, i386fbsd_core_xfer_x86_xsave_layout);
 
   /* Iterate over core file register note sections.  */
   set_gdbarch_iterate_over_regset_sections
diff --git a/gdb/i386-fbsd-tdep.c b/gdb/i386-fbsd-tdep.c
index 16ffd576323..cbbd3dcdc5f 100644
--- a/gdb/i386-fbsd-tdep.c
+++ b/gdb/i386-fbsd-tdep.c
@@ -18,6 +18,7 @@
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #include "defs.h"
+#include "gdbcore.h"
 #include "osabi.h"
 #include "regcache.h"
 #include "regset.h"
@@ -263,6 +264,34 @@ i386fbsd_core_read_xcr0 (bfd *abfd)
   return xcr0;
 }
 
+/* Implement the core_xfer_x86_xsave_layout gdbarch method.  */
+
+LONGEST
+i386fbsd_core_xfer_x86_xsave_layout (struct gdbarch *gdbarch,
+				     gdb_byte *readbuf, ULONGEST offset,
+				     ULONGEST len)
+{
+  asection *xstate = bfd_get_section_by_name (core_bfd, ".reg-xstate");
+  if (xstate == nullptr)
+    return -1;
+
+  size_t size = bfd_section_size (xstate);
+  if (size < X86_XSTATE_AVX_SIZE)
+    return -1;
+
+  if (offset > sizeof (x86_xsave_layout))
+    return -1;
+
+  x86_xsave_layout layout;
+  i387_set_xsave_layout (i386fbsd_core_read_xcr0 (core_bfd), size, &layout);
+
+  if (offset + len > sizeof (layout))
+    len = sizeof (layout) - offset;
+
+  memcpy (readbuf, ((gdb_byte *) &layout) + offset, len);
+  return len;
+}
+
 /* Implement the core_read_description gdbarch method.  */
 
 static const struct target_desc *
@@ -317,9 +346,9 @@ i386fbsd_iterate_over_regset_sections (struct gdbarch *gdbarch,
   cb (".reg2", tdep->sizeof_fpregset, tdep->sizeof_fpregset, &i386_fpregset,
       NULL, cb_data);
 
-  if (tdep->xcr0 & X86_XSTATE_AVX)
-    cb (".reg-xstate", X86_XSTATE_SIZE (tdep->xcr0),
-	X86_XSTATE_SIZE (tdep->xcr0), &i386fbsd_xstateregset,
+  if (tdep->xsave_layout.sizeof_xsave != 0)
+    cb (".reg-xstate", tdep->xsave_layout.sizeof_xsave,
+	tdep->xsave_layout.sizeof_xsave, &i386fbsd_xstateregset,
 	"XSAVE extended state", cb_data);
 }
 
@@ -372,6 +401,8 @@ i386fbsd_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
   i386_elf_init_abi (info, gdbarch);
 
   tdep->xsave_xcr0_offset = I386_FBSD_XSAVE_XCR0_OFFSET;
+  set_gdbarch_core_xfer_x86_xsave_layout
+    (gdbarch, i386fbsd_core_xfer_x86_xsave_layout);
 
   /* Iterate over core file register note sections.  */
   set_gdbarch_iterate_over_regset_sections
diff --git a/gdb/i386-fbsd-tdep.h b/gdb/i386-fbsd-tdep.h
index 76f4c20f657..305ef8416ed 100644
--- a/gdb/i386-fbsd-tdep.h
+++ b/gdb/i386-fbsd-tdep.h
@@ -25,6 +25,12 @@
 /* Get XSAVE extended state xcr0 from core dump.  */
 extern uint64_t i386fbsd_core_read_xcr0 (bfd *abfd);
 
+/* Implement the core_xfer_x86_xsave_layout gdbarch method.  */
+extern LONGEST i386fbsd_core_xfer_x86_xsave_layout (struct gdbarch *gdbarch,
+						    gdb_byte *readbuf,
+						    ULONGEST offset,
+						    ULONGEST len);
+
 /* The format of the XSAVE extended area is determined by hardware.
    Cores store the XSAVE extended area in a NT_X86_XSTATE note that
    matches the layout on Linux.  */
-- 
2.34.1