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List:       busybox
Subject:    Re: [BusyBox] Boggling at tar.c a bit...
From:       mjn3 () codepoet ! org (Manuel Novoa III)
Date:       2005-08-26 14:35:20
Message-ID: 20050826143520.GA20611 () codepoet ! org
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On Thu, Aug 25, 2005 at 11:39:59PM -0500, Rob Landley wrote:
> What does the #ifdef __gnuc__ bit do?

Looks like it wraps some code to try to prevent gcc from throwing
warnings about unused vars.

> We have a volatile local variable (vfork_exec_errno), which is interacting 
> with vfork in a way that seems unnecessarily subtle.  (Do parent and child 
> really reliably share a stack there?  Why did the threading people need 
> kernel support for thread local storage then?)

Of course they share a stack... the code is using vfork.  Apparently
they wanted the child code to pass back the errno value to the parent
on failure.  Since vfork_exec_errno is modified by the child in the 'if'
block and checked by the parent in the 'else' block, it needs to be
qualified as volatile.

Manuel


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