On June 8, 2016 12:38:36 PM PDT, "H. Peter Anvin" <h...@linux.intel.com> wrote: >From: "H. Peter Anvin" <h...@zytor.com> > >gcc 6+ has the ability to let flags (actually, conditions, which are >specific combinations of flags) to be used directly as asm() outputs. >The syntax for that is "=@cc<cc>" where <cc> is the same set of >letters that would be used in a j<cc> or set<cc> instruction >(e.g. "=@ccz" to test the ZF flag.) > >This patchset by itself reduces the size of the x86-64 kernel by >0.12%, from a baseline of 4.7-rc2 built with gcc 6.1 (first line is >with the patchset, the second one is without): > > text data bss dec hex filename > >68245656 41004339 20533248 129783243 7bc55cb >o.i386-allconfig/vmlinux >68355716 41008499 20533248 129897463 7be13f7 >o.i386-allconfig/vmlinux > >127384005 129742359 38150144 295276508 11998fdc >o.x86_64-allconfig/vmlinux >127538765 129742295 38150144 295431204 119bec24 >o.x86_64-allconfig/vmlinux > >v2: fix a conflict between <linux/random.h> and <asm/archrandom.h> > discovered by Ingo Molnar. There are a few places in x86-specific > code where we need all of <arch/archrandom.h> even when > xCONFIG_ARCH_RANDOM is disabled, so <linux/random.h> does not > suffice. Only the <asm/archrandom.h> patch has been changed; > since it is a little bit different from the others I have moved it > to the end.
I should probably clarify one thing: the output type *must* be bool for the flags output. Fortunately, not only does it also work for the older compilers, but it sometimes allows GCC to generate better code, which is why I have made the change unconditionally. -- Sent from my Android device with K-9 Mail. Please excuse brevity and formatting.
