From: Linus Torvalds <torvalds@linux-foundation.org>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Anders Larsen <al@alarsen.net>, Arnd Bergmann <arnd@arndb.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] [RFC v2] qnx: avoid -Wstringop-overread warning, again
Date: Mon, 20 Sep 2021 10:26:21 -0700 [thread overview]
Message-ID: <CAHk-=wi=CZ_fsUwDQCBbgPB4MTFx1ywgyERjFb7DNUk9Pix_Nw@mail.gmail.com> (raw)
In-Reply-To: <20210920121208.54732-1-arnd@kernel.org>
[-- Attachment #1: Type: text/plain, Size: 1050 bytes --]
On Mon, Sep 20, 2021 at 5:12 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> + /*
> + * work around gcc-11.x using the first field it observes
> + * to determing the actual length
> + * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578
> + */
> + char __empty[0];
> + char de_name[];
Ugh. That looks _really_ hacky.
It sounds like we can avoid the gcc bug if we just always use
"de->de_name[]". Then we don't need to depend on magical behavior
about one particular gcc version and a strange empty array in front of
it.
IOW, something like the attached simpler thing that just does that
"always use de_name[]" and has a comment about why we don't do the
natural thing
Also, just what version of gcc is the broken one? You say "gcc-11",
but I certainly don't see it with _my_ version of gcc-11, so can we
(just for that comment) document more precisely what version you have
(or possibly what config you use to trigger it).
Linus
[-- Attachment #2: patch.diff --]
[-- Type: text/x-patch, Size: 2210 bytes --]
fs/qnx4/dir.c | 27 ++++++++++++++++++---------
1 file changed, 18 insertions(+), 9 deletions(-)
diff --git a/fs/qnx4/dir.c b/fs/qnx4/dir.c
index 2a66844b7ff8..d60806efe090 100644
--- a/fs/qnx4/dir.c
+++ b/fs/qnx4/dir.c
@@ -20,12 +20,24 @@
* depending on the status field in the last byte. The
* first byte is where the name start either way, and a
* zero means it's empty.
+ *
+ * Also, due to a bug in gcc, we don't want to use the
+ * real (differently sized) name arrays in the inode and
+ * link entries, but always the 'de_name[]' one in the
+ * fake struct entry.
+ *
+ * See
+ *
+ * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578#c6
+ *
+ * for details - but basically gcc will take the size of
+ * the 'name' array from one of the used entries randomly.
*/
union qnx4_directory_entry {
struct {
- char de_name;
- char de_pad[62];
- char de_status;
+ const char de_name[48];
+ u8 de_pad[15];
+ u8 de_status;
};
struct qnx4_inode_entry inode;
struct qnx4_link_info link;
@@ -53,29 +65,26 @@ static int qnx4_readdir(struct file *file, struct dir_context *ctx)
ix = (ctx->pos >> QNX4_DIR_ENTRY_SIZE_BITS) % QNX4_INODES_PER_BLOCK;
for (; ix < QNX4_INODES_PER_BLOCK; ix++, ctx->pos += QNX4_DIR_ENTRY_SIZE) {
union qnx4_directory_entry *de;
- const char *name;
offset = ix * QNX4_DIR_ENTRY_SIZE;
de = (union qnx4_directory_entry *) (bh->b_data + offset);
- if (!de->de_name)
+ if (!de->de_name[0])
continue;
if (!(de->de_status & (QNX4_FILE_USED|QNX4_FILE_LINK)))
continue;
if (!(de->de_status & QNX4_FILE_LINK)) {
size = sizeof(de->inode.di_fname);
- name = de->inode.di_fname;
ino = blknum * QNX4_INODES_PER_BLOCK + ix - 1;
} else {
size = sizeof(de->link.dl_fname);
- name = de->link.dl_fname;
ino = ( le32_to_cpu(de->link.dl_inode_blk) - 1 ) *
QNX4_INODES_PER_BLOCK +
de->link.dl_inode_ndx;
}
- size = strnlen(name, size);
+ size = strnlen(de->de_name, size);
QNX4DEBUG((KERN_INFO "qnx4_readdir:%.*s\n", size, name));
- if (!dir_emit(ctx, name, size, ino, DT_UNKNOWN)) {
+ if (!dir_emit(ctx, de->de_name, size, ino, DT_UNKNOWN)) {
brelse(bh);
return 0;
}
next prev parent reply other threads:[~2021-09-20 21:27 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-20 12:12 [PATCH] [RFC v2] qnx: avoid -Wstringop-overread warning, again Arnd Bergmann
2021-09-20 17:26 ` Linus Torvalds [this message]
2021-09-21 8:18 ` Arnd Bergmann
2021-09-21 15:15 ` Anders Larsen
2021-09-21 15:40 ` Linus Torvalds
2021-09-21 15:49 ` Anders Larsen
2021-09-21 15:51 ` Linus Torvalds
2021-09-21 16:56 ` Arnd Bergmann
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