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

1 files changed, 14 insertions, 2 deletions

diff --git a/lib/libc/stdio/findfp.c b/lib/libc/stdio/findfp.c
index b8bb5af..6a68958 100644
--- a/lib/libc/stdio/findfp.c
+++ b/lib/libc/stdio/findfp.c
@@ -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;