diff mbox series

media: gspca/gl860-mi1320: avoid -Wstring-concatenation warning

Message ID 20210927122024.941874-1-arnd@kernel.org (mailing list archive)
State New, archived
Headers show
Series media: gspca/gl860-mi1320: avoid -Wstring-concatenation warning | expand

Commit Message

Arnd Bergmann Sept. 27, 2021, 12:20 p.m. UTC 
From: Arnd Bergmann <arnd@arndb.de>

Newer clang versions are suspicious of definitions that mix concatenated
strings with comma-separated arrays of strings, this has found real bugs
elsewhere, but this seems to be a false positive:

drivers/media/usb/gspca/gl860/gl860-mi1320.c:62:37: error: suspicious concatenation of string literals in an array initialization; did you mean to separate the elements with a comma? [-Werror,-Wstring-concatenation]
        "\xd3\x02\xd4\x28\xd5\x01\xd0\x02" "\xd1\x18\xd2\xc1"
                                           ^
                                          ,
drivers/media/usb/gspca/gl860/gl860-mi1320.c:62:2: note: place parentheses around the string literal to silence warning
        "\xd3\x02\xd4\x28\xd5\x01\xd0\x02" "\xd1\x18\xd2\xc1"

Use the extra parentheses as suggested in the warning message.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/media/usb/gspca/gl860/gl860-mi1320.c | 24 ++++++++++----------
 1 file changed, 12 insertions(+), 12 deletions(-)

Comments

Hans Verkuil Oct. 4, 2021, 10:55 a.m. UTC | #1 
Hi Arnd,

On 27/09/2021 14:20, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> Newer clang versions are suspicious of definitions that mix concatenated
> strings with comma-separated arrays of strings, this has found real bugs
> elsewhere, but this seems to be a false positive:
> 
> drivers/media/usb/gspca/gl860/gl860-mi1320.c:62:37: error: suspicious concatenation of string literals in an array initialization; did you mean to separate the elements with a comma? [-Werror,-Wstring-concatenation]
>         "\xd3\x02\xd4\x28\xd5\x01\xd0\x02" "\xd1\x18\xd2\xc1"
>                                            ^
>                                           ,
> drivers/media/usb/gspca/gl860/gl860-mi1320.c:62:2: note: place parentheses around the string literal to silence warning
>         "\xd3\x02\xd4\x28\xd5\x01\xd0\x02" "\xd1\x18\xd2\xc1"
> 
> Use the extra parentheses as suggested in the warning message.

I noticed that gl860-ov9655.c uses the same construct, doesn't that produce the
same warning?

Also, does clang only warn about 'static u8 *tbl[]' initializers, or also
for 'static u8 *tbl' initializers (i.e. not a pointer array) with the same
string concatenation?

I made a patch that replaces these ugly hex strings with compound initializers:

static u8 *tbl_640[] = {
        (u8[]){
                0x0d, 0x80, 0xf1, 0x08, 0x03, 0x04, 0xf1, 0x04,
                0x04, 0x05, 0xf1, 0x02, 0x07, 0x01, 0xf1, 0x7c,
                0x08, 0x00, 0xf1, 0x0e, 0x21, 0x80, 0xf1, 0x00,
                0x0d, 0x00, 0xf1, 0x08, 0xf0, 0x00, 0xf1, 0x01,
                0x34, 0x10, 0xf1, 0x10, 0x3a, 0x43, 0xf1, 0x00,
                0xa6, 0x05, 0xf1, 0x02, 0xa9, 0x04, 0xf1, 0x04,
                0xa7, 0x02, 0xf1, 0x81, 0xaa, 0x01, 0xf1, 0xe2,
                0xae, 0x0c, 0xf1, 0x09
        }, (u8[]){
                0xf0, 0x00, 0xf1, 0x02, 0x39, 0x03, 0xf1, 0xfc,
                0x3b, 0x04, 0xf1, 0x04, 0x57, 0x01, 0xf1, 0xb6,
                0x58, 0x02, 0xf1, 0x0d, 0x5c, 0x1f, 0xf1, 0x19,
                0x5d, 0x24, 0xf1, 0x1e, 0x64, 0x5e, 0xf1, 0x1c,
                0xd2, 0x00, 0xf1, 0x00, 0xcb, 0x00, 0xf1, 0x01
        }, (u8[]){
                0xd3, 0x02, 0xd4, 0x10, 0xd5, 0x81, 0xd0, 0x02,
                0xd1, 0x08, 0xd2, 0xe1
        }
};

but it clang also warns about 'static u8 *tbl' multi-string initializers,
then it would make sense to replace all these hex-strings. It's rather
ugly.

Regards,

	Hans

> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/media/usb/gspca/gl860/gl860-mi1320.c | 24 ++++++++++----------
>  1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/media/usb/gspca/gl860/gl860-mi1320.c b/drivers/media/usb/gspca/gl860/gl860-mi1320.c
> index 0749fe13160f..1253eb145c99 100644
> --- a/drivers/media/usb/gspca/gl860/gl860-mi1320.c
> +++ b/drivers/media/usb/gspca/gl860/gl860-mi1320.c
> @@ -49,44 +49,44 @@ static struct validx tbl_post_unset_alt[] = {
>  	{0x0061, 0x0000}, {0x0068, 0x000d},
>  };
>  
> -static u8 *tbl_1280[] = {
> +static u8 *tbl_1280[] = {(
>  	"\x0d\x80\xf1\x08\x03\x04\xf1\x00" "\x04\x05\xf1\x02\x05\x00\xf1\xf1"
>  	"\x06\x00\xf1\x0d\x20\x01\xf1\x00" "\x21\x84\xf1\x00\x0d\x00\xf1\x08"
>  	"\xf0\x00\xf1\x01\x34\x00\xf1\x00" "\x9b\x43\xf1\x00\xa6\x05\xf1\x00"
>  	"\xa9\x04\xf1\x00\xa1\x05\xf1\x00" "\xa4\x04\xf1\x00\xae\x0a\xf1\x08"
> -	,
> +	), (
>  	"\xf0\x00\xf1\x02\x3a\x05\xf1\xf1" "\x3c\x05\xf1\xf1\x59\x01\xf1\x47"
>  	"\x5a\x01\xf1\x88\x5c\x0a\xf1\x06" "\x5d\x0e\xf1\x0a\x64\x5e\xf1\x1c"
>  	"\xd2\x00\xf1\xcf\xcb\x00\xf1\x01"
> -	,
> +	), (
>  	"\xd3\x02\xd4\x28\xd5\x01\xd0\x02" "\xd1\x18\xd2\xc1"
> -};
> +)};
>  
> -static u8 *tbl_800[] = {
> +static u8 *tbl_800[] = { (
>  	"\x0d\x80\xf1\x08\x03\x03\xf1\xc0" "\x04\x05\xf1\x02\x05\x00\xf1\xf1"
>  	"\x06\x00\xf1\x0d\x20\x01\xf1\x00" "\x21\x84\xf1\x00\x0d\x00\xf1\x08"
>  	"\xf0\x00\xf1\x01\x34\x00\xf1\x00" "\x9b\x43\xf1\x00\xa6\x05\xf1\x00"
>  	"\xa9\x03\xf1\xc0\xa1\x03\xf1\x20" "\xa4\x02\xf1\x5a\xae\x0a\xf1\x08"
> -	,
> +	), (
>  	"\xf0\x00\xf1\x02\x3a\x05\xf1\xf1" "\x3c\x05\xf1\xf1\x59\x01\xf1\x47"
>  	"\x5a\x01\xf1\x88\x5c\x0a\xf1\x06" "\x5d\x0e\xf1\x0a\x64\x5e\xf1\x1c"
>  	"\xd2\x00\xf1\xcf\xcb\x00\xf1\x01"
> -	,
> +	), (
>  	"\xd3\x02\xd4\x18\xd5\x21\xd0\x02" "\xd1\x10\xd2\x59"
> -};
> +)};
>  
> -static u8 *tbl_640[] = {
> +static u8 *tbl_640[] = {(
>  	"\x0d\x80\xf1\x08\x03\x04\xf1\x04" "\x04\x05\xf1\x02\x07\x01\xf1\x7c"
>  	"\x08\x00\xf1\x0e\x21\x80\xf1\x00" "\x0d\x00\xf1\x08\xf0\x00\xf1\x01"
>  	"\x34\x10\xf1\x10\x3a\x43\xf1\x00" "\xa6\x05\xf1\x02\xa9\x04\xf1\x04"
>  	"\xa7\x02\xf1\x81\xaa\x01\xf1\xe2" "\xae\x0c\xf1\x09"
> -	,
> +	), (
>  	"\xf0\x00\xf1\x02\x39\x03\xf1\xfc" "\x3b\x04\xf1\x04\x57\x01\xf1\xb6"
>  	"\x58\x02\xf1\x0d\x5c\x1f\xf1\x19" "\x5d\x24\xf1\x1e\x64\x5e\xf1\x1c"
>  	"\xd2\x00\xf1\x00\xcb\x00\xf1\x01"
> -	,
> +	), (
>  	"\xd3\x02\xd4\x10\xd5\x81\xd0\x02" "\xd1\x08\xd2\xe1"
> -};
> +)};
>  
>  static s32 tbl_sat[] = {0x25, 0x1d, 0x15, 0x0d, 0x05, 0x4d, 0x55, 0x5d, 0x2d};
>  static s32 tbl_bright[] = {0, 8, 0x10, 0x20, 0x30, 0x40, 0x50, 0x60, 0x70};
>
Arnd Bergmann Oct. 4, 2021, 11:38 a.m. UTC | #2 
On Mon, Oct 4, 2021 at 12:55 PM Hans Verkuil <hverkuil@xs4all.nl> wrote:
>
> Hi Arnd,
>
> On 27/09/2021 14:20, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > Newer clang versions are suspicious of definitions that mix concatenated
> > strings with comma-separated arrays of strings, this has found real bugs
> > elsewhere, but this seems to be a false positive:
> >
> > drivers/media/usb/gspca/gl860/gl860-mi1320.c:62:37: error: suspicious concatenation of string literals in an array initialization; did you mean to separate the elements with a comma? [-Werror,-Wstring-concatenation]
> >         "\xd3\x02\xd4\x28\xd5\x01\xd0\x02" "\xd1\x18\xd2\xc1"
> >                                            ^
> >                                           ,
> > drivers/media/usb/gspca/gl860/gl860-mi1320.c:62:2: note: place parentheses around the string literal to silence warning
> >         "\xd3\x02\xd4\x28\xd5\x01\xd0\x02" "\xd1\x18\xd2\xc1"
> >
> > Use the extra parentheses as suggested in the warning message.
>
> I noticed that gl860-ov9655.c uses the same construct, doesn't that produce the
> same warning?

Curiously, it does not. I tried reproducing this in godbolt.org,
see https://godbolt.org/z/W6K69qcz3

For some reason, clang only warns about some of those, and it appears to
depend on the ratio between string concatenations and array elements.

> Also, does clang only warn about 'static u8 *tbl[]' initializers, or also
> for 'static u8 *tbl' initializers (i.e. not a pointer array) with the same
> string concatenation?

When there is only one element rather than an array, it does not warn,
because it's not a mix of concatenation and array elements.

> I made a patch that replaces these ugly hex strings with compound initializers:
>
> static u8 *tbl_640[] = {
>         (u8[]){
>                 0x0d, 0x80, 0xf1, 0x08, 0x03, 0x04, 0xf1, 0x04,
>                 0x04, 0x05, 0xf1, 0x02, 0x07, 0x01, 0xf1, 0x7c,
>                 0x08, 0x00, 0xf1, 0x0e, 0x21, 0x80, 0xf1, 0x00,
>                 0x0d, 0x00, 0xf1, 0x08, 0xf0, 0x00, 0xf1, 0x01,
>                 0x34, 0x10, 0xf1, 0x10, 0x3a, 0x43, 0xf1, 0x00,
>                 0xa6, 0x05, 0xf1, 0x02, 0xa9, 0x04, 0xf1, 0x04,
>                 0xa7, 0x02, 0xf1, 0x81, 0xaa, 0x01, 0xf1, 0xe2,
>                 0xae, 0x0c, 0xf1, 0x09
>         }, (u8[]){
>                 0xf0, 0x00, 0xf1, 0x02, 0x39, 0x03, 0xf1, 0xfc,
>                 0x3b, 0x04, 0xf1, 0x04, 0x57, 0x01, 0xf1, 0xb6,
>                 0x58, 0x02, 0xf1, 0x0d, 0x5c, 0x1f, 0xf1, 0x19,
>                 0x5d, 0x24, 0xf1, 0x1e, 0x64, 0x5e, 0xf1, 0x1c,
>                 0xd2, 0x00, 0xf1, 0x00, 0xcb, 0x00, 0xf1, 0x01
>         }, (u8[]){
>                 0xd3, 0x02, 0xd4, 0x10, 0xd5, 0x81, 0xd0, 0x02,
>                 0xd1, 0x08, 0xd2, 0xe1
>         }
> };
>
> but it clang also warns about 'static u8 *tbl' multi-string initializers,
> then it would make sense to replace all these hex-strings. It's rather
> ugly.

This seems fine.

       Arnd
diff mbox series

Patch

diff --git a/drivers/media/usb/gspca/gl860/gl860-mi1320.c b/drivers/media/usb/gspca/gl860/gl860-mi1320.c
index 0749fe13160f..1253eb145c99 100644
--- a/drivers/media/usb/gspca/gl860/gl860-mi1320.c
+++ b/drivers/media/usb/gspca/gl860/gl860-mi1320.c
@@ -49,44 +49,44 @@  static struct validx tbl_post_unset_alt[] = {
 	{0x0061, 0x0000}, {0x0068, 0x000d},
 };
 
-static u8 *tbl_1280[] = {
+static u8 *tbl_1280[] = {(
 	"\x0d\x80\xf1\x08\x03\x04\xf1\x00" "\x04\x05\xf1\x02\x05\x00\xf1\xf1"
 	"\x06\x00\xf1\x0d\x20\x01\xf1\x00" "\x21\x84\xf1\x00\x0d\x00\xf1\x08"
 	"\xf0\x00\xf1\x01\x34\x00\xf1\x00" "\x9b\x43\xf1\x00\xa6\x05\xf1\x00"
 	"\xa9\x04\xf1\x00\xa1\x05\xf1\x00" "\xa4\x04\xf1\x00\xae\x0a\xf1\x08"
-	,
+	), (
 	"\xf0\x00\xf1\x02\x3a\x05\xf1\xf1" "\x3c\x05\xf1\xf1\x59\x01\xf1\x47"
 	"\x5a\x01\xf1\x88\x5c\x0a\xf1\x06" "\x5d\x0e\xf1\x0a\x64\x5e\xf1\x1c"
 	"\xd2\x00\xf1\xcf\xcb\x00\xf1\x01"
-	,
+	), (
 	"\xd3\x02\xd4\x28\xd5\x01\xd0\x02" "\xd1\x18\xd2\xc1"
-};
+)};
 
-static u8 *tbl_800[] = {
+static u8 *tbl_800[] = { (
 	"\x0d\x80\xf1\x08\x03\x03\xf1\xc0" "\x04\x05\xf1\x02\x05\x00\xf1\xf1"
 	"\x06\x00\xf1\x0d\x20\x01\xf1\x00" "\x21\x84\xf1\x00\x0d\x00\xf1\x08"
 	"\xf0\x00\xf1\x01\x34\x00\xf1\x00" "\x9b\x43\xf1\x00\xa6\x05\xf1\x00"
 	"\xa9\x03\xf1\xc0\xa1\x03\xf1\x20" "\xa4\x02\xf1\x5a\xae\x0a\xf1\x08"
-	,
+	), (
 	"\xf0\x00\xf1\x02\x3a\x05\xf1\xf1" "\x3c\x05\xf1\xf1\x59\x01\xf1\x47"
 	"\x5a\x01\xf1\x88\x5c\x0a\xf1\x06" "\x5d\x0e\xf1\x0a\x64\x5e\xf1\x1c"
 	"\xd2\x00\xf1\xcf\xcb\x00\xf1\x01"
-	,
+	), (
 	"\xd3\x02\xd4\x18\xd5\x21\xd0\x02" "\xd1\x10\xd2\x59"
-};
+)};
 
-static u8 *tbl_640[] = {
+static u8 *tbl_640[] = {(
 	"\x0d\x80\xf1\x08\x03\x04\xf1\x04" "\x04\x05\xf1\x02\x07\x01\xf1\x7c"
 	"\x08\x00\xf1\x0e\x21\x80\xf1\x00" "\x0d\x00\xf1\x08\xf0\x00\xf1\x01"
 	"\x34\x10\xf1\x10\x3a\x43\xf1\x00" "\xa6\x05\xf1\x02\xa9\x04\xf1\x04"
 	"\xa7\x02\xf1\x81\xaa\x01\xf1\xe2" "\xae\x0c\xf1\x09"
-	,
+	), (
 	"\xf0\x00\xf1\x02\x39\x03\xf1\xfc" "\x3b\x04\xf1\x04\x57\x01\xf1\xb6"
 	"\x58\x02\xf1\x0d\x5c\x1f\xf1\x19" "\x5d\x24\xf1\x1e\x64\x5e\xf1\x1c"
 	"\xd2\x00\xf1\x00\xcb\x00\xf1\x01"
-	,
+	), (
 	"\xd3\x02\xd4\x10\xd5\x81\xd0\x02" "\xd1\x08\xd2\xe1"
-};
+)};
 
 static s32 tbl_sat[] = {0x25, 0x1d, 0x15, 0x0d, 0x05, 0x4d, 0x55, 0x5d, 0x2d};
 static s32 tbl_bright[] = {0, 8, 0x10, 0x20, 0x30, 0x40, 0x50, 0x60, 0x70};