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Re: Using stpcpy

From: David Engster
Subject: Re: Using stpcpy
Date: Sat, 27 Dec 2014 21:03:10 +0100
User-agent: Gnus/5.13001 (Ma Gnus v0.10) Emacs/24.3.91 (gnu/linux)

Eli Zaretskii writes:
>> From: cg <address@hidden>
>> Date: Sat, 27 Dec 2014 19:57:07 +0800
>> On 12/27/2014 3:45 PM, Eli Zaretskii wrote:
>> >
>> > Sorry, I don't understand this: there's no call to stpcpy on line 350
>> > of ntlib.c, or anywhere else in ntlib.c, actually.  That line calls
>> >
>> Yes, I was confused by the error message too, and found ntlib.c
>> didin't use stpcpy at all. It looks like it has something to do with
>> compiler optimization.
>> So I tried to use different optimization flags, and this error only
>> happens when -O2 or -Ofast is used as CFLAGS:
>> ./autogen.sh
>> export CFLASG=-O0 # no error
>> #export CFLASG=-O1 # no error
>> #export CFLASG=-O2 # error!
>> #export CFLASG=-Ofast # error!
>> ./confgure
>> make
>> I am using msys2.
> Incredible as it sounds, in an optimized build, GCC (sometimes?) calls
> stpcpy even though the source calls strcpy, provided that the
> prototype of stpcpy is in scope.  In this case, ntlib.c includes
> windows.h, which includes string.h, which comes from lib/string.h,
> which declares the prototype of stpcpy, and that is enough to trigger
> this misfeature.
> I fixed this by switching the order of the libraries, as suggested,
> but only because doing so is TRT in general.

Yes, it seems gcc optimizes this because of the following strlen
call. You can disable this optimization with -fno-optimize-strlen.


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