svn commit: r292809 - head/lib/libc/stdio

[Warner Losh]

Author: imp
Date: Sun Dec 27 23:04:11 2015
New Revision: 292809
URL: https://svnweb.freebsd.org/changeset/base/292809

Log:
  The FILE structure has a mbstate_t in it. This structure needs to be
  aligned on a int64_t boundary. However, when we allocate the array of
  these structures, we use ALIGNBYTES which defaults to sizeof(int) on
  arm, i386 and others. The i386 stuff can handle unaligned accesses
  seemlessly. However, arm cannot. Take this into account when creating
  the array of FILEs, and add some comments about why.
  
  Differential Revision: https://reviews.freebsd.org/D4708

Modified:
  head/lib/libc/stdio/findfp.c

Modified: head/lib/libc/stdio/findfp.c
==============================================================================
--- head/lib/libc/stdio/findfp.c	Sun Dec 27 23:04:10 2015	(r292808)
+++ head/lib/libc/stdio/findfp.c	Sun Dec 27 23:04:11 2015	(r292809)
@@ -41,6 +41,7 @@ __FBSDID("$FreeBSD$");
 #include <unistd.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdint.h>
 #include <string.h>
 
 #include <spinlock.h>
@@ -96,11 +97,22 @@ moreglue(int n)
 	struct glue *g;
 	static FILE empty = { ._fl_mutex = PTHREAD_MUTEX_INITIALIZER };
 	FILE *p;
+	size_t align;
 
-	g = (struct glue *)malloc(sizeof(*g) + ALIGNBYTES + n * sizeof(FILE));
+	/*
+	 * FILE has a mbstate_t variable. This variable tries to be int64_t
+	 * aligned through its definition. int64_t may be larger than void *,
+	 * which is the size traditionally used for ALIGNBYTES.  So, use our own
+	 * rounding instead of the MI ALIGN macros. If for some reason
+	 * ALIGNBYTES is larger than int64_t, respect that too. There appears to
+	 * be no portable way to ask for FILE's alignment requirements other
+	 * than just knowing here.
+	 */
+	align = MAX(ALIGNBYTES, sizeof(int64_t));
+	g = (struct glue *)malloc(sizeof(*g) + align + n * sizeof(FILE));
 	if (g == NULL)
 		return (NULL);
-	p = (FILE *)ALIGN(g + 1);
+	p = (FILE *)roundup((uintptr_t)(g + 1), align);
 	g->next = NULL;
 	g->niobs = n;
 	g->iobs = p;