[llvm-bugs] [Bug 38881] New: Clang warning extending into system headers (-Werror, -Wsign-compare)

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38881

            Bug ID: 38881
           Summary: Clang warning extending into system headers
                    (-Werror,-Wsign-compare)
           Product: clang
           Version: 7.0
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: raj.khem at gmail.com
                CC: llvm-bugs at lists.llvm.org

Attached example when compiled with clang for linux/musl systems emits a
warnings in system headers 

Testcase
=============================
#define _GNU_SOURCE
#include <sys/socket.h>

int foo(struct cmsghdr *header, struct msghdr msg) {
        header = CMSG_NXTHDR(&msg, header);
        return 0;
}

=============================
error:

../../../../../../../workspace/sources/libkcapi/lib/kcapi-kernel-if.c:25:11:
error: comparison of integers of different signs: 'unsigned long' and 'long'
[-Werror,-Wsign-compare]
        header = CMSG_NXTHDR(&msg, header);
                 ^~~~~~~~~~~~~~~~~~~~~~~~~
/mnt/a/oe/build/tmp/work/core2-64-bec-linux-musl/libkcapi/1.1.3+git999-r0/recipe-sysroot/usr/include/sys/socket.h:299:44:
note: expanded from macro 'CMSG_NXTHDR'
        __CMSG_LEN(cmsg) + sizeof(struct cmsghdr) >= __MHDR_END(mhdr) -
(unsigned char *)(cmsg) \
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
=============================

cmdline:

x86_64-bec-linux-musl-clang
--sysroot=/mnt/a/oe/build/tmp/work/core2-64-bec-linux-musl/libkcapi/1.1.3+git999-r0/recipe-sysroot
 -c lib/kcapi-kernel-if.c -O -Werror -Wextra

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