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Date: Sun, 2 Aug 2020 20:24:29 +0200
From: Petr Skocik <pskocik@...il.com>
To: musl@...ts.openwall.com
Subject: Musl's FD_{SET,ISSET,CLR} macros from sys/select.h trigger gcc's
-Wsign-conversion warnings
Example:
#include <sys/select.h>
void f(int X)
{
fd_set set;
FD_ZERO(&set);
FD_SET(X,&set);
FD_CLR(X+1,&set);
(void)FD_ISSET(X+2,&set);
}
results in
fds.c: In function ‘f’: fds.c:17:2: warning: conversion to ‘long
unsigned int’ from ‘int’ may change the sign of the result
[-Wsign-conversion] 17 | FD_SET(X,&set); | ^~~~~~ fds.c:17:2: warning:
conversion to ‘long unsigned int’ from ‘int’ may change the sign of the
result [-Wsign-conversion] fds.c:18:2: warning: conversion to ‘long
unsigned int’ from ‘int’ may change the sign of the result
[-Wsign-conversion] 18 | FD_CLR(X+1,&set); | ^~~~~~ fds.c:18:2: warning:
conversion to ‘long unsigned int’ from ‘int’ may change the sign of the
result [-Wsign-conversion] fds.c:19:8: warning: conversion to ‘long
unsigned int’ from ‘int’ may change the sign of the result
[-Wsign-conversion] 19 | (void)FD_ISSET(X+2,&set); | ^~~~~~~~
fds.c:19:8: warning: conversion to ‘long unsigned int’ from ‘int’ may
change the sign of the result [-Wsign-conversion]
on `gcc -Wconversion`.
Adding an int-cast before each `sizeof` in the definition of these
macros eliminates the warning:
#define FD_SET(d, s) ((s)->fds_bits[(d)/(8*(int)sizeof(long))] |=
(1UL<<((d)%(8*(int)sizeof(long)))))
#define FD_CLR(d, s) ((s)->fds_bits[(d)/(8*(int)sizeof(long))] &=
~(1UL<<((d)%(8*(int)sizeof(long)))))
#define FD_ISSET(d, s) !!((s)->fds_bits[(d)/(8*(int)sizeof(long))] &
(1UL<<((d)%(8*(int)sizeof(long)))))
You might want to add them.
Regards,
Petr Skocik
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