Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner AT cygwin DOT com Mail-Followup-To: cygwin AT cygwin DOT com Delivered-To: mailing list cygwin AT cygwin DOT com Message-ID: <002701c2aada$874d2e90$fe47893e@pomello> From: "Max Bowsher" To: , References: <3E00A20100008131 AT mail-8 DOT tiscalinet DOT it> Subject: Re: Strange behaviour of gcc Date: Mon, 23 Dec 2002 23:25:00 -0000 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 fabrizio_ge-wolit AT tiscali DOT it wrote: > Can somebody explain why gcc (version 3.2 20020927) on Cygwin does > this? Type this simple C program > > void func(void){ > struct {unsigned char data[3985];}var; > } > > and compile with > > gcc -c filename.c > > Then type > > nm filename.o > > The output is > > 00000000 b .bss > 00000000 d .data > 00000000 t .text > U __alloca > 00000000 T _func > > Why on earth is the symbol __alloca doing there? > > Just change the program to > > void func(void){ > struct {unsigned char data[3984];}var; > } > > and compile it. This time, nm's output is > > 00000000 b .bss > 00000000 d .data > 00000000 t .text > 00000000 T _func > > as it should. Is there a reason why the symbol __alloca appears? Yes. Gcc's optimizer chose to make a large amount of local variable allocation into an alloca call. Does it matter? Max. -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Bug reporting: http://cygwin.com/bugs.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/