[PATCH v2 2/3] Detect SVE when reading aarch64 core files

[Alan Hayward <alan.hayward@arm.com>]

Add a function which reads the vector length from the SVE section within an
aarch64 core file.

The SVE section in a core file contains a header followed by the registers.
All macros to parse access this structure.

2018-07-30  Alan Hayward  <alan.hayward@arm.com>

	* aarch64-linux-tdep.c (struct struct_contents): Add struct.
	(SVE_HEADER_SIZE): Add Macro.
	(SVE_HEADER_WRITE): Likewise.
	(SVE_HEADER_READ): Likewise.
	(aarch64_linux_core_read_vq): Add function.
	(aarch64_linux_core_read_description): Check for SVE section.
---
 gdb/aarch64-linux-tdep.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 71 insertions(+), 3 deletions(-)

diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
index 7b63cddbe6..f9a95950da 100644
--- a/gdb/aarch64-linux-tdep.c
+++ b/gdb/aarch64-linux-tdep.c
@@ -219,6 +219,75 @@ const struct regset aarch64_linux_fpregset =
     regcache_supply_regset, regcache_collect_regset
   };
 
+/* Description of the fields in an SVE header at the start of a SVE regset.  */
+
+struct struct_contents {
+  int len;
+  int offset;
+} sve_header[] =
+    {
+      { 4, 0 },		/* __u32 size.  */
+      { 4, 4 },		/* __u32 max_size.  */
+      { 2, 8 },		/* __u16 vl.  */
+      { 2, 10 },	/* __u16 max_vl.  */
+      { 2, 12 },	/* __u16 flags.  */
+      { 2, 14 },	/* __u16 reserved.  */
+      { -1, 16 }
+    };
+
+#define SVE_HEADER_SIZE (sve_header[6].offset)
+
+#define SVE_HEADER_WRITE(header, entry, byte_order, value) \
+  store_unsigned_integer ((gdb_byte *) header + sve_header[entry].offset, \
+			  sve_header[entry].len, byte_order, value)
+
+#define SVE_HEADER_READ(header, entry, byte_order) \
+  extract_unsigned_integer ((gdb_byte *) header + sve_header[entry].offset, \
+			    sve_header[entry].len, byte_order)
+
+/* Get VQ value from SVE section in the core dump.  */
+
+static uint64_t
+aarch64_linux_core_read_vq (struct gdbarch *gdbarch, bfd *abfd)
+{
+  gdb_byte header[SVE_HEADER_SIZE];
+  enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
+  asection *sve_section = bfd_get_section_by_name (abfd, ".reg-aarch-sve");
+
+  if (!sve_section)
+    {
+      /* No SVE state.  */
+      return 0;
+    }
+
+  size_t size = bfd_section_size (abfd, sve_section);
+
+  /* Check extended state size.  */
+  if (size < SVE_HEADER_SIZE)
+    {
+      warning (_("'.reg-aarch-sve' section in core file too small."));
+      return 0;
+    }
+
+  if (!bfd_get_section_contents (abfd, sve_section, header, 0, SVE_HEADER_SIZE))
+    {
+      warning (_("Couldn't read sve header from "
+		 "'.reg-aarch-sve' section in core file."));
+      return 0;
+    }
+
+  uint64_t vq = sve_vq_from_vl (SVE_HEADER_READ (header, 2, byte_order));
+
+  if (vq > AARCH64_MAX_SVE_VQ)
+    {
+      warning (_("sve header invalid in "
+		 "'.reg-aarch-sve' section in core file."));
+      return 0;
+    }
+
+  return vq;
+}
+
 /* Implement the "regset_from_core_section" gdbarch method.  */
 
 static void
@@ -233,8 +302,7 @@ aarch64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
       &aarch64_linux_fpregset, NULL, cb_data);
 }
 
-/* Implement the "core_read_description" gdbarch method.  SVE not yet
-   supported.  */
+/* Implement the "core_read_description" gdbarch method.  */
 
 static const struct target_desc *
 aarch64_linux_core_read_description (struct gdbarch *gdbarch,
@@ -245,7 +313,7 @@ aarch64_linux_core_read_description (struct gdbarch *gdbarch,
   if (target_auxv_search (target, AT_HWCAP, &aarch64_hwcap) != 1)
     return NULL;
 
-  return aarch64_read_description (0);
+  return aarch64_read_description (aarch64_linux_core_read_vq (gdbarch, abfd));
 }
 
 /* Implementation of `gdbarch_stap_is_single_operand', as defined in
-- 
2.15.2 (Apple Git-101.1)