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Message-ID: <542175EF.4040703@t-online.de>
Date: Tue, 23 Sep 2014 15:30:23 +0200
From: Christian Franke <Christian DOT Franke AT t-online DOT de>
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To: cygwin AT cygwin DOT com
Subject: Re: ffs problem in windows64
References: <CAHAq8pG0xMtSLJYs_u8OW4Z1Loovpyzzyo4oLBZQPqYsWFUU6w AT mail DOT gmail DOT com> <54216D72 DOT 2070307 AT cs DOT umass DOT edu>
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Eliot Moss wrote:
> On 9/23/2014 8:47 AM, Paulo César Pereira de Andrade wrote:
>>    Hi,
>>
>>    I am almost done porting https://savannah.gnu.org/projects/lightning
>> to cygwin and windows64 abi. But I found a problem with the ffs 
>> function.
>>
>>    The test case is simple:
>>
>> $ cat x.c
>> extern int ffs(int);
>> int main(void) {
>> long l = 0x80000000;
>> int i = ffs((int)l);
>> return 0;
>> }
>>
>> $ gcc -O0 -g3 x.c
>>
>> $ ./a.exe
>> Segmentation fault (...)
>
> WJFFM in 32 bit cygwin.
>

It fails under 64 bit cygwin.

This segfaults if gcc -fno-builtin option is used:
   ffs(0x80000000)

These work:
   ffs(0xc0000000)
   ffs(0x40000000)

Likely a subtle problem in table based ffs() implementation in 
winsup/cygwin/syscalls.cc if only upper bit is set. The newlib version 
of ffs() works.

Christian


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