Date: Thu, 10 Mar 2011 17:37:32 +0100 From: Roman Divacky <rdivacky@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-current@freebsd.org, Dimitry Andric <dim@freebsd.org> Subject: Re: [TESTING]: one more boot2 shrinking patch Message-ID: <20110310163732.GA38320@freebsd.org> In-Reply-To: <201103100920.58279.jhb@freebsd.org> References: <20110308173909.GA71091@freebsd.org> <201103090823.41757.jhb@freebsd.org> <4D780C34.4010509@FreeBSD.org> <201103100920.58279.jhb@freebsd.org>
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On Thu, Mar 10, 2011 at 09:20:58AM -0500, John Baldwin wrote: > On Wednesday, March 09, 2011 6:24:36 pm Dimitry Andric wrote: > > On 2011-03-09 14:23, John Baldwin wrote: > > >> gcc nor clang emits any code to initialize static type foo = 0; > > >> because it's expected that BSS is zeroed, which is not the case > > >> in boot2 so we have to initialize that explicitly > > > It used to be that if you explicitly initialized a variable to 0, it was > > > initialized to 0 in .data, but now gcc and clang recognize it is set to 0 and > > > move it to .bss. There appears to be no way to turn this feature off, > > > > Yes, there is; both gcc and clang have this option to turn it off: > > > > -fno-zero-initialized-in-bss > > If the target supports a BSS section, GCC by default puts variables > > that are initialized to zero into BSS. This can save space in the > > resulting code. > > > > This option turns off this behavior because some programs > > explicitly rely on variables going to the data section. E.g., so > > that the resulting executable can find the beginning of that > > section and/or make assumptions based on that. > > > > The default is -fzero-initialized-in-bss. > > Hah, that is better then. Thanks! I should have searched about this more > myself. :( Roman, can you try reverting the kname changes and adding this > to CFLAGS instead for both compilers? when I put -fno-zero-initialized-in-bss clang does not fit by 1.7K and gcc by 0.5K, we dont want this :) roman
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