Date: Sat, 24 Dec 2011 10:51:51 +0100 From: Matthias Andree <matthias.andree@gmx.de> To: freebsd-current@freebsd.org Subject: Re: [rfc] removing -mpreferred-stack-boundary=2 flag for i386? Message-ID: <4EF5A0B7.8050002@gmx.de> In-Reply-To: <20111223235642.GA37495@freebsd.org> References: <20111223235642.GA37495@freebsd.org>
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Am 24.12.2011 00:56, schrieb Alexander Best: > hi there, > > is -mpreferred-stack-boundary=2 really necessary for i386 builds any longer? > i built GENERIC (including modules) with and without that flag. the results > are: > > 1654496 bytes with the flag set > vs. > 1654952 bytes with the flag unset > > the gcc(1) man page states the following: > > " > This extra alignment does consume extra stack space, and generally > increases code size. Code that is sensitive to stack space usage, > such as embedded systems and operating system kernels, may want to > reduce the preferred alignment to -mpreferred-stack-boundary=2. > " > What do the numbers above have to do with *stack* alignment or size (which is a run-time figure, and cannot be statically determined if any variable-depth recursion takes place). What are those 16... numbers, anyways? How did you obtain them?
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