From: David Woodhouse <dwmw2@infradead.org>
Date: Sun, 14 May 2006 23:49:43 +0000 (+0100)
Subject: [JFFS2] Don't pack on-medium structures, because GCC emits crappy code
X-Git-Tag: v2.6.18-rc1~1105^2~106
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3e68fbb59b3d4e6b47b65e9928b5929e02179759;p=linux-2.6

[JFFS2] Don't pack on-medium structures, because GCC emits crappy code

If we use __attribute__((packed)), GCC will _also_ assume that the
structures aren't sensibly aligned, and it'll emit code to cope with
that instead of straight word load/save. This can be _very_ suboptimal
on architectures like ARM.

Ideally, we want an attribute which just tells GCC not to do any
padding, without the alignment side-effects. In the absense of that,
we'll just drop the 'packed' attribute and hope that everything stays as
it was (which to be fair is fairly much what we expect). And add some
paranoia checks in the initialisation code, which should be optimised
away completely in the normal case.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
---

diff --git a/fs/jffs2/super.c b/fs/jffs2/super.c
index ffd8e84b22..5f73de5869 100644
--- a/fs/jffs2/super.c
+++ b/fs/jffs2/super.c
@@ -320,6 +320,18 @@ static int __init init_jffs2_fs(void)
 {
 	int ret;
 
+	/* Paranoia checks for on-medium structures. If we ask GCC
+	   to pack them with __attribute__((packed)) then it _also_
+	   assumes that they're not aligned -- so it emits crappy
+	   code on some architectures. Ideally we want an attribute
+	   which means just 'no padding', without the alignment
+	   thing. But GCC doesn't have that -- we have to just
+	   hope the structs are the right sizes, instead. */
+	BUG_ON(sizeof(struct jffs2_unknown_node) != 12);
+	BUG_ON(sizeof(struct jffs2_raw_dirent) != 40);
+	BUG_ON(sizeof(struct jffs2_raw_inode) != 68);
+	BUG_ON(sizeof(struct jffs2_raw_summary) != 32);
+
 	printk(KERN_INFO "JFFS2 version 2.2."
 #ifdef CONFIG_JFFS2_FS_WRITEBUFFER
 	       " (NAND)"
@@ -327,7 +339,7 @@ static int __init init_jffs2_fs(void)
 #ifdef CONFIG_JFFS2_SUMMARY
 	       " (SUMMARY) "
 #endif
-	       " (C) 2001-2003 Red Hat, Inc.\n");
+	       " (C) 2001-2006 Red Hat, Inc.\n");
 
 	jffs2_inode_cachep = kmem_cache_create("jffs2_i",
 					     sizeof(struct jffs2_inode_info),
diff --git a/include/linux/jffs2.h b/include/linux/jffs2.h
index cf792bb3c7..228ad72f7d 100644
--- a/include/linux/jffs2.h
+++ b/include/linux/jffs2.h
@@ -82,15 +82,15 @@
 
 typedef struct {
 	uint32_t v32;
-} __attribute__((packed))  jint32_t;
+} jint32_t;
 
 typedef struct {
 	uint32_t m;
-} __attribute__((packed))  jmode_t;
+} jmode_t;
 
 typedef struct {
 	uint16_t v16;
-} __attribute__((packed)) jint16_t;
+} jint16_t;
 
 struct jffs2_unknown_node
 {
@@ -99,7 +99,7 @@ struct jffs2_unknown_node
 	jint16_t nodetype;
 	jint32_t totlen; /* So we can skip over nodes we don't grok */
 	jint32_t hdr_crc;
-} __attribute__((packed));
+};
 
 struct jffs2_raw_dirent
 {
@@ -117,7 +117,7 @@ struct jffs2_raw_dirent
 	jint32_t node_crc;
 	jint32_t name_crc;
 	uint8_t name[0];
-} __attribute__((packed));
+};
 
 /* The JFFS2 raw inode structure: Used for storage on physical media.  */
 /* The uid, gid, atime, mtime and ctime members could be longer, but
@@ -149,7 +149,7 @@ struct jffs2_raw_inode
 	jint32_t data_crc;   /* CRC for the (compressed) data.  */
 	jint32_t node_crc;   /* CRC for the raw inode (excluding data)  */
 	uint8_t data[0];
-} __attribute__((packed));
+};
 
 struct jffs2_raw_summary
 {
@@ -163,7 +163,7 @@ struct jffs2_raw_summary
 	jint32_t sum_crc;	/* summary information crc */
 	jint32_t node_crc; 	/* node crc */
 	jint32_t sum[0]; 	/* inode summary info */
-} __attribute__((packed));
+};
 
 union jffs2_node_union
 {