Date: Thu, 6 Aug 2015 14:45:45 -0700 From: Andy Lutomirski <luto@...nel.org> To: x86@...nel.org, linux-kernel@...r.kernel.org Cc: 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>, Andy Lutomirski <luto@...capital.net> Subject: [PATCH] x86/vdso: Emit a GNU hash 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. 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
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