From 6b7e26547fad7ace3dcb27a5babd2317fb9d1e12 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Thu, 6 Aug 2015 14:45:45 -0700 Subject: [PATCH] x86/vdso: Emit a GNU hash 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 Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Isaac Dunham Cc: Linus Torvalds Cc: Nathan Lynch Cc: Peter Zijlstra Cc: Rich Felker Cc: Thomas Gleixner Cc: musl@lists.openwall.com Link: http://lkml.kernel.org/r/fd56cc057a2d62ab31c56a48d04fccb435b3fd4f.1438897382.git.luto@kernel.org Signed-off-by: Ingo Molnar --- 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 96c06172c2ff..a3d0767a6b29 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 -- 2.20.1