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Date: Wed, 16 Feb 2022 10:03:30 -0800
From: Khem Raj <raj.khem@...il.com>
To: musl@...ts.openwall.com
Subject: Re: -Wsign-conversion warning on ARM when using CMSG_NXTHDR
On Wed, Feb 16, 2022 at 4:42 AM Christian Eggers <ceggers@...i.de> wrote:
> Toolchain: Yocto Linux with poky-tiny
> Host platform: openSUSE 15.3 x86_64
> Target platform: arm-poky-linux-musleabi (armv7, 32 bit)
>
> When I try to compile libkcapi [1] [2] with current
> Yocto/Openembedded master branch, I get the following compiler error:
>
> | ../git/lib/kcapi-kernel-if.c: In function '_kcapi_common_send_meta':
> | ../git/lib/kcapi-kernel-if.c:193:26: error: unsigned conversion from
> 'long int' to 'long unsigned int' changes value from '-4' to '4294967292'
> [-Werror=sign-conversion]
> | 193 | header = CMSG_NXTHDR(&msg, header);
> | | ^~~~~~~~~~~
> | ../git/lib/kcapi-kernel-if.c:193:26: error: unsigned conversion from
> 'long int' to 'long unsigned int' changes value from '-4' to '4294967292'
> [-Werror=sign-conversion]
> | ../git/lib/kcapi-kernel-if.c:213:26: error: unsigned conversion from
> 'long int' to 'long unsigned int' changes value from '-4' to '4294967292'
> [-Werror=sign-conversion]
> | 213 | header = CMSG_NXTHDR(&msg, header);
> | | ^~~~~~~~~~~
> | ../git/lib/kcapi-kernel-if.c:213:26: error: unsigned conversion from
> 'long int' to 'long unsigned int' changes value from '-4' to '4294967292'
> [-Werror=sign-conversion]
>
> Note: libcapi uses the '-Werror' and '-Wconversion' flags.
>
> For testing, I created a minimal code snipset (cmsg.c):
>
> #include <stddef.h>
> #include <sys/socket.h>
>
> void foo(void)
> {
> struct msghdr msg = {0};
> struct cmsghdr *header = NULL;
>
> header = CMSG_FIRSTHDR(&msg);
> header = CMSG_NXTHDR(&msg, header);
> }
>
> # arm-poky-linux-musleabi-gcc --sysroot=<...> -Werror -Wconversion -c -o
> cmsg.o cmsg.c
> cmsg.c: In function 'foo':
> cmsg.c:10:18: error: unsigned conversion from 'long int' to 'long unsigned
> int' changes value from '-4' to '4294967292' [-Werror=sign-conversion]
> 10 | header = CMSG_NXTHDR(&msg, header);
> | ^~~~~~~~~~~
> cmsg.c:10:18: error: unsigned conversion from 'long int' to 'long unsigned
> int' changes value from '-4' to '4294967292' [-Werror=sign-conversion]
>
>
> When replace CMSG_NXTHDR() by the expanded macro code, I get the following
> errors:
>
> cmsg.c: In function 'foo':
> cmsg.c:12:46: error: unsigned conversion from 'long int' to 'long unsigned
> int' changes value from '-4' to '4294967292' [-Werror=sign-conversion]
> 12 | (((header)->cmsg_len + sizeof(long) - 1) & ~(long)(sizeof(long) - 1))
> + sizeof(struct cmsghdr) >= ((unsigned char *)(&msg)->msg_control +
> (&msg)->msg_controllen) - (unsigned char *)(header) \
> | ^
> cmsg.c:13:99: error: unsigned conversion from 'long int' to 'long unsigned
> int' changes value from '-4' to '4294967292' [-Werror=sign-conversion]
> 13 | ? 0 : (struct cmsghdr *)((unsigned char *)(header) +
> (((header)->cmsg_len + sizeof(long) - 1) & ~(long)(sizeof(long) - 1))));
> | ^
>
> check https://github.com/smuellerDD/libkcapi/pull/131
libkcapi has dropped using -Werror
>
> [1]
> https://git.openembedded.org/meta-openembedded/tree/meta-oe/recipes-crypto/libkcapi?h=master
> [2]
> https://github.com/smuellerDD/libkcapi/tree/2936ecd060c299157ac880650ba2c9fd94d27bb1
>
>
>
> _______________________________________________________
> Christian
> Eggers
> Software Engineer
> ARRI
> Arnold & Richter Cine Technik GmbH & Co. Betriebs KG
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