diff mbox

[0/5] obstacks again

Message ID 54518D50.1090503@cs.ucla.edu
State Not Applicable
Headers show

Commit Message

Paul Eggert Oct. 30, 2014, 12:58 a.m. UTC
Joseph S. Myers wrote:
> Note that we can't use <stdalign.h> in glibc sources unless we move to
> requiring GCC >= 4.7

Ah, thanks for mentioning that; the attached patch should fix that.  I pushed 
this into gnulib.
From d91a04a3dfc05b42031e8fd00af2cd29b6fa585d Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Wed, 29 Oct 2014 16:15:41 -0700
Subject: [PATCH] obstack: prefer __alignof__ to alignof

This is for portability to pre-4.7 GCC when compiling glibc.
See Joseph S. Myers in:
http://sourceware.org/ml/libc-alpha/2014-10/msg00703.html
* lib/obstack.c (__alignof__) [!_LIBC && !__GNUC__]:
New macro, defined by including and using <alignof.h>.
(MAX): New macro.
(DEFAULT_ALIGNMENT, DEFAULT_ROUNDING): Redefine in terms of these.
Do not use enums as they are not portable to some broken compilers.
* modules/obstack (Depends-on): Depend on alignof, not stdalign.
---
 ChangeLog       | 11 +++++++++++
 lib/obstack.c   | 32 ++++++++++++++++++--------------
 modules/obstack |  2 +-
 3 files changed, 30 insertions(+), 15 deletions(-)
diff mbox

Patch

diff --git a/ChangeLog b/ChangeLog
index ffe7285..cea54fc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,16 @@ 
 2014-10-29  Paul Eggert  <eggert@cs.ucla.edu>
 
+	obstack: prefer __alignof__ to alignof
+	This is for portability to pre-4.7 GCC when compiling glibc.
+	See Joseph S. Myers in:
+	http://sourceware.org/ml/libc-alpha/2014-10/msg00703.html
+	* lib/obstack.c (__alignof__) [!_LIBC && !__GNUC__]:
+	New macro, defined by including and using <alignof.h>.
+	(MAX): New macro.
+	(DEFAULT_ALIGNMENT, DEFAULT_ROUNDING): Redefine in terms of these.
+	Do not use enums as they are not portable to some broken compilers.
+	* modules/obstack (Depends-on): Depend on alignof, not stdalign.
+
 	obstack: prefer alignof to calculating alignments by hand
 	* lib/obstack.c: Include <stdalign.h>.
 	(struct fooalign): Remove.
diff --git a/lib/obstack.c b/lib/obstack.c
index 03281ae..ba7dff3 100644
--- a/lib/obstack.c
+++ b/lib/obstack.c
@@ -48,26 +48,30 @@ 
 #endif
 
 #ifndef _OBSTACK_ELIDE_CODE
-# include <stdalign.h>
+# if !defined _LIBC && !defined __GNUC__
+#  include <alignof.h>
+#  define __alignof__(type) alignof_type (type)
+# endif
 # include <stdlib.h>
 # include <stdint.h>
 
+# ifndef MAX
+#  define MAX(a,b) ((a) > (b) ? (a) : (b))
+# endif
+
 /* Determine default alignment.  */
-union fooround
-{
-  uintmax_t i;
-  long double d;
-  void *p;
-};
+
 /* If malloc were really smart, it would round addresses to DEFAULT_ALIGNMENT.
    But in fact it might be less smart and round addresses to as much as
-   DEFAULT_ROUNDING.  So we prepare for it to do that.  */
-enum
-{
-  DEFAULT_ALIGNMENT = alignof (union fooround),
-  DEFAULT_ROUNDING = sizeof (union fooround)
-};
-
+   DEFAULT_ROUNDING.  So we prepare for it to do that.
+
+   DEFAULT_ALIGNMENT cannot be an enum constant; see gnulib's alignof.h.  */
+#define DEFAULT_ALIGNMENT MAX (__alignof__ (long double),		      \
+                               MAX (__alignof__ (uintmax_t),		      \
+                                    __alignof__ (void *)))
+#define DEFAULT_ROUNDING MAX (sizeof (long double),			      \
+                               MAX (sizeof (uintmax_t),			      \
+                                    sizeof (void *)))
 
 /* Define a macro that either calls functions with the traditional malloc/free
    calling interface, or calls functions with the mmalloc/mfree interface
diff --git a/modules/obstack b/modules/obstack
index c2c6390..36dc444 100644
--- a/modules/obstack
+++ b/modules/obstack
@@ -6,9 +6,9 @@  lib/obstack.h
 lib/obstack.c
 
 Depends-on:
+alignof
 gettext-h
 exitfail
-stdalign
 stdint
 stdlib