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From: "johan162 at gmail dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sources.redhat.com
Subject: [Bug libc/12373] New: FD_SET macro gives warning with -Wconversion (with solution)
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http://sourceware.org/bugzilla/show_bug.cgi?id=3D12373

           Summary: FD_SET macro gives warning with -Wconversion (with
                    solution)
           Product: glibc
           Version: 2.11
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper.fsp@gmail.com
        ReportedBy: johan162@gmail.com


It is not possible to compile the following code with gcc 4.4.1 and extra
warnings enabled without warning

#include <sys/select.h>
int main(void)
{
    fd_set fds;
    int    fd =3D 0;
    FD_ZERO(&fds);
    FD_SET(fd, &fds);
    return 0;
}

Compiling this:

gcc -Werror -Wconversion wtst.c
cc1: warnings being treated as errors
wtst.c: In function =E2=80=98main=E2=80=99:
wtst.c:8: error: conversion to =E2=80=98unsigned int=E2=80=99 from =E2=80=
=98int=E2=80=99 may change the sign of
the result
wtst.c:8: error: conversion to =E2=80=98unsigned int=E2=80=99 from =E2=80=
=98int=E2=80=99 may change the sign of
the result

gcc --version
gcc (SUSE Linux) 4.4.1 [gcc-4_4-branch revision 150839]

The problem stems from the inline assmebler expansion where there is type o=
f fd
clashes with the return type of the sizeof() operator.

This can easily be corrected by changing the macro from the existing:

  __asm__ __volatile__ ("btsl %1,%0" : "=3Dm" (((&fds)->__fds_bits)[((fd) /=
 (8 *
sizeof (__fd_mask)))]) : "r" (((int) (fd)) % (8 * sizeof (__fd_mask))) :
"cc","memory");

to

  __asm__ __volatile__ ("btsl %1,%0" : "=3Dm"
(((&fds)->__fds_bits)[((unsigned)(fd) / (8 * sizeof (__fd_mask)))]) : "r"
(((unsigned) (fd)) % (8 * sizeof (__fd_mask))) : "cc","memory");

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