gdb: Restructure type_align and gdbarch_type_align

This commit restructures the relationship between the type_align
function and the gdbarch_type_align method.

The problem being addressed with this commit is this; previously the
type_align function was structured so that for "basic" types (int,
float, etc) the gdbarch_type_align hook was called, which for
"compound" types (arrays, structs, etc) the common type_align code has
a fixed method for how to extract a "basic" type and would then call
itself on that "basic" type.

The problem is that if an architecture wants to modify the alignment
rules for a "compound" type then this is not currently possible.

In the revised structure, all types pass through the
gdbarch_type_align method.  If this method returns 0 then this
indicates that the architecture has no special rules for this type,
and GDB should apply the default rules for alignment.  However, the
architecture is free to provide an alignment for any type, both
"basic" and "compound".

After this commit the default alignment rules now all live in the
type_align function, the default_type_align only ever returns 0,
meaning apply the default rules.

I've updated the 3 targets (arc, i386, and nios2) that already
override the gdbarch_type_align method to fit the new scheme.

Tested on X86-64/GNU Linux with no regressions.

gdb/ChangeLog:

	* arc-tdep.c (arc_type_align): Provide alignment for basic types,
	return 0 for other types.
	* arch-utils.c (default_type_align): Always return 0.
	* gdbarch.h: Regenerate.
	* gdbarch.sh (type_align): Extend comment.
	* gdbtypes.c (type_align): Add additional comments, always call
	gdbarch_type_align before applying the default rules.
	* i386-tdep.c (i386_type_align): Return 0 as the default rule,
	generic code will then apply a suitable default.
	* nios2-tdep.c (nios2_type_align): Provide alignment for basic
	types, return 0 for other types.

8 files changed, 74 insertions, 13 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index b0fce99..07f3c47 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,17 @@
+2019-02-27  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* arc-tdep.c (arc_type_align): Provide alignment for basic types,
+	return 0 for other types.
+	* arch-utils.c (default_type_align): Always return 0.
+	* gdbarch.h: Regenerate.
+	* gdbarch.sh (type_align): Extend comment.
+	* gdbtypes.c (type_align): Add additional comments, always call
+	gdbarch_type_align before applying the default rules.
+	* i386-tdep.c (i386_type_align): Return 0 as the default rule,
+	generic code will then apply a suitable default.
+	* nios2-tdep.c (nios2_type_align): Provide alignment for basic
+	types, return 0 for other types.
+
 2019-02-27  Joel Brobecker  <brobecker@adacore.com>
 
 	* NEWS: Create a new section for the next release branch.
diff --git a/gdb/arc-tdep.c b/gdb/arc-tdep.c
index cd2762c..235fb27 100644
--- a/gdb/arc-tdep.c
+++ b/gdb/arc-tdep.c
@@ -1963,8 +1963,27 @@ arc_tdesc_init (struct gdbarch_info info, const struct target_desc **tdesc,
 static ULONGEST
 arc_type_align (struct gdbarch *gdbarch, struct type *type)
 {
-  type = check_typedef (type);
-  return std::min<ULONGEST> (4, TYPE_LENGTH (type));
+  switch (TYPE_CODE (type))
+    {
+    case TYPE_CODE_PTR:
+    case TYPE_CODE_FUNC:
+    case TYPE_CODE_FLAGS:
+    case TYPE_CODE_INT:
+    case TYPE_CODE_RANGE:
+    case TYPE_CODE_FLT:
+    case TYPE_CODE_ENUM:
+    case TYPE_CODE_REF:
+    case TYPE_CODE_RVALUE_REF:
+    case TYPE_CODE_CHAR:
+    case TYPE_CODE_BOOL:
+    case TYPE_CODE_DECFLOAT:
+    case TYPE_CODE_METHODPTR:
+    case TYPE_CODE_MEMBERPTR:
+      type = check_typedef (type);
+      return std::min<ULONGEST> (4, TYPE_LENGTH (type));
+    default:
+      return 0;
+    }
 }
 
 /* Implement the "init" gdbarch method.  */
diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
index d2e27d9..52a08da 100644
--- a/gdb/arch-utils.c
+++ b/gdb/arch-utils.c
@@ -993,7 +993,7 @@ default_in_indirect_branch_thunk (gdbarch *gdbarch, CORE_ADDR pc)
 ULONGEST
 default_type_align (struct gdbarch *gdbarch, struct type *type)
 {
-  return type_length_units (check_typedef (type));
+  return 0;
 }
 
 void
diff --git a/gdb/gdbarch.h b/gdb/gdbarch.h
index 5b265a4..7561837 100644
--- a/gdb/gdbarch.h
+++ b/gdb/gdbarch.h
@@ -1589,7 +1589,10 @@ extern void set_gdbarch_disassembler_options (struct gdbarch *gdbarch, char ** d
 extern const disasm_options_and_args_t * gdbarch_valid_disassembler_options (struct gdbarch *gdbarch);
 extern void set_gdbarch_valid_disassembler_options (struct gdbarch *gdbarch, const disasm_options_and_args_t * valid_disassembler_options);
 
-/* Type alignment. */
+/* Type alignment override method.  Return the architecture specific
+   alignment required for TYPE.  If there is no special handling
+   required for TYPE then return the value 0, GDB will then apply the
+   default rules as laid out in gdbtypes.c:type_align. */
 
 typedef ULONGEST (gdbarch_type_align_ftype) (struct gdbarch *gdbarch, struct type *type);
 extern ULONGEST gdbarch_type_align (struct gdbarch *gdbarch, struct type *type);
diff --git a/gdb/gdbarch.sh b/gdb/gdbarch.sh
index d53bbcc..48fcebd 100755
--- a/gdb/gdbarch.sh
+++ b/gdb/gdbarch.sh
@@ -1171,7 +1171,10 @@ v;const char *;disassembler_options_implicit;;;0;0;;0;pstring (gdbarch->disassem
 v;char **;disassembler_options;;;0;0;;0;pstring_ptr (gdbarch->disassembler_options)
 v;const disasm_options_and_args_t *;valid_disassembler_options;;;0;0;;0;host_address_to_string (gdbarch->valid_disassembler_options)
 
-# Type alignment.
+# Type alignment override method.  Return the architecture specific
+# alignment required for TYPE.  If there is no special handling
+# required for TYPE then return the value 0, GDB will then apply the
+# default rules as laid out in gdbtypes.c:type_align.
 m;ULONGEST;type_align;struct type *type;type;;default_type_align;;0
 
 EOF
diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index 0d29339..63dec3c 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -2992,11 +2992,17 @@ type_raw_align (struct type *type)
 unsigned
 type_align (struct type *type)
 {
+  /* Check alignment provided in the debug information.  */
   unsigned raw_align = type_raw_align (type);
   if (raw_align != 0)
     return raw_align;
 
-  ULONGEST align = 0;
+  /* Allow the architecture to provide an alignment.  */
+  struct gdbarch *arch = get_type_arch (type);
+  ULONGEST align = gdbarch_type_align (arch, type);
+  if (align != 0)
+    return align;
+
   switch (TYPE_CODE (type))
     {
     case TYPE_CODE_PTR:
@@ -3013,10 +3019,7 @@ type_align (struct type *type)
     case TYPE_CODE_DECFLOAT:
     case TYPE_CODE_METHODPTR:
     case TYPE_CODE_MEMBERPTR:
-      {
-	struct gdbarch *arch = get_type_arch (type);
-	align = gdbarch_type_align (arch, type);
-      }
+      align = type_length_units (check_typedef (type));
       break;
 
     case TYPE_CODE_ARRAY:
diff --git a/gdb/i386-tdep.c b/gdb/i386-tdep.c
index 663d510..bc9ba75 100644
--- a/gdb/i386-tdep.c
+++ b/gdb/i386-tdep.c
@@ -8348,7 +8348,7 @@ i386_type_align (struct gdbarch *gdbarch, struct type *type)
 	return 4;
     }
 
-  return TYPE_LENGTH (type);
+  return 0;
 }
 
 
diff --git a/gdb/nios2-tdep.c b/gdb/nios2-tdep.c
index aa49a57..ee45db9 100644
--- a/gdb/nios2-tdep.c
+++ b/gdb/nios2-tdep.c
@@ -2233,8 +2233,27 @@ nios2_get_longjmp_target (struct frame_info *frame, CORE_ADDR *pc)
 static ULONGEST
 nios2_type_align (struct gdbarch *gdbarch, struct type *type)
 {
-  type = check_typedef (type);
-  return std::min<ULONGEST> (4, TYPE_LENGTH (type));
+  switch (TYPE_CODE (type))
+    {
+    case TYPE_CODE_PTR:
+    case TYPE_CODE_FUNC:
+    case TYPE_CODE_FLAGS:
+    case TYPE_CODE_INT:
+    case TYPE_CODE_RANGE:
+    case TYPE_CODE_FLT:
+    case TYPE_CODE_ENUM:
+    case TYPE_CODE_REF:
+    case TYPE_CODE_RVALUE_REF:
+    case TYPE_CODE_CHAR:
+    case TYPE_CODE_BOOL:
+    case TYPE_CODE_DECFLOAT:
+    case TYPE_CODE_METHODPTR:
+    case TYPE_CODE_MEMBERPTR:
+      type = check_typedef (type);
+      return std::min<ULONGEST> (4, TYPE_LENGTH (type));
+    default:
+      return 0;
+    }
 }
 
 /* Implement the gcc_target_options gdbarch method.  */