From 97b67ae559947f1e208439a1bf6a734da3087006 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Tue, 4 Nov 2014 08:50:48 +0000 Subject: x86-64: Use RIP-relative addressing for most per-CPU accesses Observing that per-CPU data (in the SMP case) is reachable by exploiting 64-bit address wraparound (building on the default kernel load address being at 16Mb), the one byte shorter RIP-relative addressing form can be used for most per-CPU accesses. The one exception are the "stable" reads, where the use of the "P" operand modifier prevents the compiler from using RIP-relative addressing, but is unavoidable due to the use of the "p" constraint (side note: with gcc 4.9.x the intended effect of this isn't being achieved anymore, see gcc bug 63637). With the dependency on the minimum kernel load address, arbitrarily low values for CONFIG_PHYSICAL_START are now no longer possible. A link time assertion is being added, directing to the need to increase that value when it triggers. Signed-off-by: Jan Beulich Link: http://lkml.kernel.org/r/5458A1780200007800044A9D@mail.emea.novell.com Signed-off-by: Thomas Gleixner --- arch/x86/kernel/vmlinux.lds.S | 2 ++ 1 file changed, 2 insertions(+) (limited to 'arch/x86/kernel/vmlinux.lds.S') diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index 49edf2dd3613..00bf300fd846 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -186,6 +186,8 @@ SECTIONS * start another segment - init. */ PERCPU_VADDR(INTERNODE_CACHE_BYTES, 0, :percpu) + ASSERT(SIZEOF(.data..percpu) < CONFIG_PHYSICAL_START, + "per-CPU data too large - increase CONFIG_PHYSICAL_START") #endif INIT_TEXT_SECTION(PAGE_SIZE) -- cgit