Date: Wed, 5 Jan 2011 10:02:51 -0500 From: John Baldwin <jhb@freebsd.org> To: Nathan Whitehorn <nwhitehorn@freebsd.org> Cc: Gleb Kurtsou <gleb.kurtsou@gmail.com>, src-committers@freebsd.org, svn-src-all@freebsd.org, Dimitry Andric <dim@freebsd.org>, svn-src-head@freebsd.org, Alexander Best <arundel@freebsd.org> Subject: Re: svn commit: r216977 - in head/libexec/rtld-elf: amd64 i386 Message-ID: <201101051002.51598.jhb@freebsd.org> In-Reply-To: <4D248540.3030602@freebsd.org> References: <201101042051.p04KpSGk054564@svn.freebsd.org> <201101050928.30748.jhb@freebsd.org> <4D248540.3030602@freebsd.org>
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On Wednesday, January 05, 2011 9:50:40 am Nathan Whitehorn wrote: > On 01/05/11 08:28, John Baldwin wrote: > > On Wednesday, January 05, 2011 8:36:06 am Dimitry Andric wrote: > >> On 2011-01-05 13:59, John Baldwin wrote: > >>>> Why not to add NO_HWFLOAT knob (or similar) into makefile > >>>> infrastructure. And set CFLAGS accordingly, depending on CC, arch, etc. > >>>> These flags are getting rather common in tree. > >>> It strikes me that we really want clang/gcc to have some sort of > >>> '-mno-hwfloat' so we don't keep having to add new flags in the future. > >> This is not just about floats, clang can also use SSE/AVX instructions > >> for e.g. memset(), memcpy() and the like, or even for structure > >> assignments. > > Yes, but the thing that all these extensions have in common is that they use > > FPU state (i.e. subject to DNA traps, managed via *SAVE and *RSTOR, etc.) > > and that is the problem with using them in boot code or rtld. What I would > > want a -mno-hwfloat flag to do is to disable use of anything that would > > require working FPU state handling. > > You would also want this to be cross-platform, in which case it's more > than floating point. E.g. on powerpc, you also want to disable both FP > and vector extensions, which use separate sets of instructions and > registers. I guess overriding CPU type to be something very old (386?) > potentially deoptimizes the code? Hmm, I don't know if this is generically MI, but at least for x86 having a single -mno-sse-xmm-mmx-anything-registers-please would be useful I think. -- John Baldwin
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