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[Bug libc/14210] New: warning when using FD_SET() with -Wsign-conversion and _FORTIFY_SOURCE


http://sourceware.org/bugzilla/show_bug.cgi?id=14210

             Bug #: 14210
           Summary: warning when using FD_SET() with -Wsign-conversion and
                    _FORTIFY_SOURCE
           Product: glibc
           Version: 2.15
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: unassigned@sourceware.org
        ReportedBy: vapier@gentoo.org
                CC: drepper.fsp@gmail.com
    Classification: Unclassified
            Target: x86_64-linux-gnu


starting with glibc-2.15, trying to use FD_SET according to the API results in
build time warnings when using -Wsign-conversion and fortification

$ cat test.c
#include <sys/select.h>
int main(int argc, char *argv[])
{
    int fd = argc;
    fd_set fds;
    FD_ZERO(&fds);
    FD_SET(fd, &fds);
    return argv[0][fd];
}

$ gcc test.c -c -Wsign-conversion -O2 -Werror -D_FORTIFY_SOURCE=2
error: conversion to 'long unsigned int' from 'int' may change the sign of the
result [-Werror=sign-conversion]

this is because FD_SET assigns the int fd to an "unsigned int long" without a
cast, and that triggers signed warnings

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