[PATCH 0/2] btrfs-progs: build warning hunting routine

[PATCH 0/2] btrfs-progs: build warning hunting routine

[Qu Wenruo]

Two small cosmetic warning hunting with latest GCC/e2fsprogs.

Qu Wenruo (2):
  btrfs-progs: convert/ext2: fix the pointer sign warning
  btrfs-progs: Fix seemly wrong format overflow warning

 common/fsfeatures.c   | 2 +-
 convert/source-ext2.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

-- 
2.27.0

[PATCH 1/2] btrfs-progs: convert/ext2: fix the pointer sign warning

[Qu Wenruo]

[WARNING]
When compiling btrfs-progs, there is one warning from convert ext2 code:
  convert/source-ext2.c: In function 'ext2_open_fs':
  convert/source-ext2.c:91:44: warning: pointer targets in passing argument 1 of 'strndup' differ in signedness [-Wpointer-sign]
     91 |  cctx->volume_name = strndup(ext2_fs->super->s_volume_name, 16);
        |                              ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
        |                                            |
        |                                            __u8 * {aka unsigned char *}
  In file included from ./kerncompat.h:25,
                   from convert/source-ext2.c:19:
  /usr/include/string.h:175:35: note: expected 'const char *' but argument is of type '__u8 *' {aka 'unsigned char *'}
    175 | extern char *strndup (const char *__string, size_t __n)
        |                       ~~~~~~~~~~~~^~~~~~~~

The toolchain involved is:
- GCC 10.1.0
- e2fsprogs 1.45.6

[CAUSE]
Obviously, in the offending e2fsprogs, the volume lable is using u8,
which is unsigned char, not char.

  /*078*/	__u8	s_volume_name[EXT2_LABEL_LEN];	/* volume name, no NUL? */

[FIX]
Just do a forced conversion to suppress the warning is enough.
I don't think we need to apply -Wnopointer-sign yet.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 convert/source-ext2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/convert/source-ext2.c b/convert/source-ext2.c
index f248249f..f11ef651 100644
--- a/convert/source-ext2.c
+++ b/convert/source-ext2.c
@@ -88,7 +88,7 @@ static int ext2_open_fs(struct btrfs_convert_context *cctx, const char *name)
 	cctx->blocksize = ext2_fs->blocksize;
 	cctx->block_count = ext2_fs->super->s_blocks_count;
 	cctx->total_bytes = ext2_fs->blocksize * ext2_fs->super->s_blocks_count;
-	cctx->volume_name = strndup(ext2_fs->super->s_volume_name, 16);
+	cctx->volume_name = strndup((char *)ext2_fs->super->s_volume_name, 16);
 	cctx->first_data_block = ext2_fs->super->s_first_data_block;
 	cctx->inodes_count = ext2_fs->super->s_inodes_count;
 	cctx->free_inodes_count = ext2_fs->super->s_free_inodes_count;
-- 
2.27.0

[PATCH 2/2] btrfs-progs: Fix seemly wrong format overflow warning

[Qu Wenruo]

[WARNING]
When compiling btrfs-progs, the following warning pops up:
  In file included from /usr/include/stdio.h:867,
                   from ./kerncompat.h:22,
                   from common/fsfeatures.c:17:
  In function 'printf',
      inlined from 'process_features' at common/fsfeatures.c:192:4,
      inlined from 'btrfs_process_runtime_features' at common/fsfeatures.c:205:2:
  /usr/include/bits/stdio2.h:107:10: warning: '%s' directive argument is null [-Wformat-overflow=]
    107 |   return __printf_chk (__USE_FORTIFY_LEVEL - 1, __fmt, __va_arg_pack ());
        |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This only occur with default make parameters. If compiling with D=1, the
warning just disappears.

The involved tool chain is:
- GCC 10.1.0

[CAUSE]
The offending code is:
  static void process_features(u64 flags, enum feature_source source)
  {
  ...
		if (flags & feat->flag) {
			printf("Turning ON incompat feature '%s': %s\n",
				feat->name, feat->desc);
		}
  ...
  }

Currently, there is no runtime/fs feature without a name nor
description.
So we shouldn't hit a feature with NULL as name nor description.

This looks like a bug in GCC though.

[WORKAROUND]
However can workaround it by doing an explicit check on feat->name and
feat->desc to teach GCC not to do a wrong warning.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 common/fsfeatures.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/common/fsfeatures.c b/common/fsfeatures.c
index ae075daf..195a77c3 100644
--- a/common/fsfeatures.c
+++ b/common/fsfeatures.c
@@ -188,7 +188,7 @@ static void process_features(u64 flags, enum feature_source source)
 	for (i = 0; i < array_size; i++) {
 		const struct btrfs_feature *feat = get_feature(i, source);
 
-		if (flags & feat->flag) {
+		if (flags & feat->flag && feat->name && feat->desc) {
 			printf("Turning ON incompat feature '%s': %s\n",
 				feat->name, feat->desc);
 		}
-- 
2.27.0

Re: [PATCH 0/2] btrfs-progs: build warning hunting routine

[David Sterba]

On Tue, Jun 23, 2020 at 01:48:02PM +0800, Qu Wenruo wrote:
> Two small cosmetic warning hunting with latest GCC/e2fsprogs.
> 
> Qu Wenruo (2):
>   btrfs-progs: convert/ext2: fix the pointer sign warning
>   btrfs-progs: Fix seemly wrong format overflow warning

Added to devel, thanks.