Date: Thu, 6 Aug 2015 15:52:42 -0700 From: Andy Lutomirski <luto@...capital.net> To: Andy Lutomirski <luto@...nel.org>, Anton Blanchard <anton@...ba.org>, Martin Schwidefsky <schwidefsky@...ibm.com>, Chris Metcalf <cmetcalf@...era.com>, Richard Kuo <rkuo@...eaurora.org> Cc: X86 ML <x86@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Nathan Lynch <nathan_lynch@...tor.com>, Isaac Dunham <ibid.ag@...il.com>, Rich Felker <dalias@...c.org>, "musl@...ts.openwall.com" <musl@...ts.openwall.com> Subject: Re: [PATCH] x86/vdso: Emit a GNU hash [adding lots of cc's] On Thu, Aug 6, 2015 at 2:45 PM, Andy Lutomirski <luto@...nel.org> wrote: > From: Andy Lutomirski <luto@...capital.net> > > Some dynamic loaders may be slightly faster if a GNU hash is > available. Strangely, this seems to have no effect at all on the > vdso size. > > This is unlikely to have any measurable effect on the time it takes > to resolve vdso symbols (since there are so few of them). In some > contexts, it can be a win for a different reason: if every DSO has a > GNU hash section, then libc can avoid calculating SysV hashes at > all. Both musl and glibc appear to have this optimization. > > It's plausible that this breaks some ancient glibc version. If so, > then, depending on what glibc versions break, we could either > require COMPAT_VDSO for them or consider reverting. > Adding lots of arch vdso people. I think this would be a good thing to do in general. Want to update your arches (powerpc, arm(64), s390, tile, and hexagon -- did I miss any?)? --Andy > Signed-off-by: Andy Lutomirski <luto@...capital.net> > --- > > For review. I'll add it to my (currently empty) 4.3 pull request if > people like it, unless Ingo feels like adding it to -tip directly. > > arch/x86/entry/vdso/Makefile | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile > index e97032069f88..20f3ac53148d 100644 > --- a/arch/x86/entry/vdso/Makefile > +++ b/arch/x86/entry/vdso/Makefile > @@ -175,7 +175,7 @@ quiet_cmd_vdso = VDSO $@ > -Wl,-T,$(filter %.lds,$^) $(filter %.o,$^) && \ > sh $(srctree)/$(src)/checkundef.sh '$(NM)' '$@' > > -VDSO_LDFLAGS = -fPIC -shared $(call cc-ldoption, -Wl$(comma)--hash-style=sysv) \ > +VDSO_LDFLAGS = -fPIC -shared $(call cc-ldoption, -Wl$(comma)--hash-style=both) \ > $(call cc-ldoption, -Wl$(comma)--build-id) -Wl,-Bsymbolic $(LTO_CFLAGS) > GCOV_PROFILE := n > > -- > 2.4.3 > -- Andy Lutomirski AMA Capital Management, LLC
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