Assert that a floating type's length is at least as long as its format

This would have caught the HP/PA bug fixed in the previous patch:

 .../src/gdb/gdbtypes.c:4690: internal-error: arch_float_type: Assertion `len >= floatformat_totalsize_bytes (floatformats[0])' failed.
 A problem internal to GDB has been detected,
 further debugging may prove unreliable.
 Quit this debugging session? (y or n)

Tested on x86-64 Fedora 23, --enable-targets=all.

gdb/ChangeLog:
2016-03-09  Pedro Alves  <palves@redhat.com>

	* doublest.c (floatformat_totalsize_bytes): New function.
	(floatformat_from_type): Assert that the type's length is at least
	as long as the floatformat's totalsize.
	* doublest.h (floatformat_totalsize_bytes): New declaration.
	* gdbtypes.c (arch_float_type): Assert that the type's length is
	at least as long as the floatformat's totalsize.

4 files changed, 37 insertions, 2 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 7303c32..abb224d 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,14 @@
 2016-03-09  Pedro Alves  <palves@redhat.com>
 
+	* doublest.c (floatformat_totalsize_bytes): New function.
+	(floatformat_from_type): Assert that the type's length is at least
+	as long as the floatformat's totalsize.
+	* doublest.h (floatformat_totalsize_bytes): New declaration.
+	* gdbtypes.c (arch_float_type): Assert that the type's length is
+	at least as long as the floatformat's totalsize.
+
+2016-03-09  Pedro Alves  <palves@redhat.com>
+
 	* hppa-linux-tdep.c (hppa_linux_init_abi): Set the long double
 	format to floatformats_ieee_double.
 
diff --git a/gdb/doublest.c b/gdb/doublest.c
index 026cf42..fe06fec 100644
--- a/gdb/doublest.c
+++ b/gdb/doublest.c
@@ -693,6 +693,15 @@ static const struct floatformat *host_double_format = GDB_HOST_DOUBLE_FORMAT;
 static const struct floatformat *host_long_double_format
   = GDB_HOST_LONG_DOUBLE_FORMAT;
 
+/* See doublest.h.  */
+
+size_t
+floatformat_totalsize_bytes (const struct floatformat *fmt)
+{
+  return ((fmt->totalsize + FLOATFORMAT_CHAR_BIT - 1)
+	  / FLOATFORMAT_CHAR_BIT);
+}
+
 void
 floatformat_to_doublest (const struct floatformat *fmt,
 			 const void *in, DOUBLEST *out)
@@ -802,12 +811,16 @@ const struct floatformat *
 floatformat_from_type (const struct type *type)
 {
   struct gdbarch *gdbarch = get_type_arch (type);
+  const struct floatformat *fmt;
 
   gdb_assert (TYPE_CODE (type) == TYPE_CODE_FLT);
   if (TYPE_FLOATFORMAT (type) != NULL)
-    return TYPE_FLOATFORMAT (type)[gdbarch_byte_order (gdbarch)];
+    fmt = TYPE_FLOATFORMAT (type)[gdbarch_byte_order (gdbarch)];
   else
-    return floatformat_from_length (gdbarch, TYPE_LENGTH (type));
+    fmt = floatformat_from_length (gdbarch, TYPE_LENGTH (type));
+
+  gdb_assert (TYPE_LENGTH (type) >= floatformat_totalsize_bytes (fmt));
+  return fmt;
 }
 
 /* Extract a floating-point number of type TYPE from a target-order
diff --git a/gdb/doublest.h b/gdb/doublest.h
index ae42bdb..9522829 100644
--- a/gdb/doublest.h
+++ b/gdb/doublest.h
@@ -89,6 +89,10 @@ extern const char *floatformat_mantissa (const struct floatformat *,
 
 const struct floatformat *floatformat_from_type (const struct type *type);
 
+/* Return the floatformat's total size in host bytes.  */
+
+extern size_t floatformat_totalsize_bytes (const struct floatformat *fmt);
+
 extern DOUBLEST extract_typed_floating (const void *addr,
 					const struct type *type);
 extern void store_typed_floating (void *addr, const struct type *type,
diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index f129b0e..1af6fff 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -4682,6 +4682,15 @@ arch_float_type (struct gdbarch *gdbarch,
 
   t = arch_type (gdbarch, TYPE_CODE_FLT, bit / TARGET_CHAR_BIT, name);
   TYPE_FLOATFORMAT (t) = floatformats;
+
+  if (floatformats != NULL)
+    {
+      size_t len = TYPE_LENGTH (t);
+
+      gdb_assert (len >= floatformat_totalsize_bytes (floatformats[0]));
+      gdb_assert (len >= floatformat_totalsize_bytes (floatformats[1]));
+    }
+
   return t;
 }