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Message-ID: <002701c2aada$874d2e90$fe47893e@pomello>
From: "Max Bowsher" <maxb AT ukf DOT net>
To: <fabrizio_ge-wolit AT tiscali DOT it>, <cygwin AT cygwin DOT com>
References: <3E00A20100008131 AT mail-8 DOT tiscalinet DOT it>
Subject: Re: Strange behaviour of gcc
Date: Mon, 23 Dec 2002 23:25:00 -0000
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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.


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