From d4ae1c999171bceb0649956047f814e1996391a4 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Tue, 15 Dec 2015 14:15:43 +0100 Subject: [PATCH] x86: generate labels at the beginning of unlikely sub-sections This is to limit symbol table growth, which would be quite a bit worse if we went with the "label every unlikely sub-section contribution" approach proposed previously. Older gas doesn't support quoted symbols, yet the result looks quite bit better that way. Hence two variants get introduced, one using proper path names (including slashes and dashes) and one using path names after converting them to valid symbol names (slashes and dashes replaced). As a secondary adjustment also change the section name used with Clang. Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper --- xen/arch/x86/Rules.mk | 4 ++++ xen/include/asm-x86/asm_defns.h | 32 ++++++++++++++++++++++++++++++-- 2 files changed, 34 insertions(+), 2 deletions(-) diff --git a/xen/arch/x86/Rules.mk b/xen/arch/x86/Rules.mk index 5b8eaedb91..637d25276b 100644 --- a/xen/arch/x86/Rules.mk +++ b/xen/arch/x86/Rules.mk @@ -20,6 +20,7 @@ xenoprof := y CFLAGS += -I$(BASEDIR)/include CFLAGS += -I$(BASEDIR)/include/asm-x86/mach-generic CFLAGS += -I$(BASEDIR)/include/asm-x86/mach-default +CFLAGS += '-D__OBJECT_LABEL__=$(subst /,$$,$(subst -,_,$(subst $(BASEDIR)/,,$(CURDIR))/$@))' # Prevent floating-point variables from creeping into Xen. CFLAGS += -msoft-float @@ -29,6 +30,9 @@ $(call cc-option-add,CFLAGS,CC,-Wnested-externs) $(call as-insn-check,CFLAGS,CC,"vmcall",-DHAVE_GAS_VMX) $(call as-insn-check,CFLAGS,CC,"invept (%rax)$$(comma)%rax",-DHAVE_GAS_EPT) $(call as-insn-check,CFLAGS,CC,"rdfsbase %rax",-DHAVE_GAS_FSGSBASE) +$(call as-insn-check,CFLAGS,CC,".equ \"x\"$$(comma)1", \ + -U__OBJECT_LABEL__ -DHAVE_GAS_QUOTED_SYM \ + '-D__OBJECT_LABEL__=$(subst $(BASEDIR)/,,$(CURDIR))/$$@') x86 := y x86_32 := n diff --git a/xen/include/asm-x86/asm_defns.h b/xen/include/asm-x86/asm_defns.h index 95ea21debe..7cf440846d 100644 --- a/xen/include/asm-x86/asm_defns.h +++ b/xen/include/asm-x86/asm_defns.h @@ -93,10 +93,24 @@ void ret_from_intr(void); #ifdef __ASSEMBLY__ +#ifdef HAVE_GAS_QUOTED_SYM +#define SUBSECTION_LBL(tag) \ + .ifndef .L.tag; \ + .equ .L.tag, 1; \ + .equ __stringify(__OBJECT_LABEL__.tag), .; \ + .endif +#else +#define SUBSECTION_LBL(tag) \ + .ifndef __OBJECT_LABEL__.tag; \ + __OBJECT_LABEL__.tag:; \ + .endif +#endif + #define UNLIKELY_START(cond, tag) \ .Ldispatch.tag: \ j##cond .Lunlikely.tag; \ .subsection 1; \ + SUBSECTION_LBL(unlikely); \ .Lunlikely.tag: #define UNLIKELY_DISPATCH_LABEL(tag) \ @@ -141,9 +155,22 @@ void ret_from_intr(void); #else +#ifdef HAVE_GAS_QUOTED_SYM +#define SUBSECTION_LBL(tag) \ + ".ifndef .L." #tag "\n\t" \ + ".equ .L." #tag ", 1\n\t" \ + ".equ \"" __stringify(__OBJECT_LABEL__) "." #tag "\", .\n\t" \ + ".endif" +#else +#define SUBSECTION_LBL(tag) \ + ".ifndef " __stringify(__OBJECT_LABEL__) "." #tag "\n\t" \ + __stringify(__OBJECT_LABEL__) "." #tag ":\n\t" \ + ".endif" +#endif + #ifdef __clang__ /* clang's builtin assember can't do .subsection */ -#define UNLIKELY_START_SECTION ".pushsection .fixup,\"ax\"" +#define UNLIKELY_START_SECTION ".pushsection .text.unlikely,\"ax\"" #define UNLIKELY_END_SECTION ".popsection" #else @@ -155,7 +182,8 @@ void ret_from_intr(void); #define UNLIKELY_START(cond, tag) \ "j" #cond " .Lunlikely%=.tag;\n\t" \ - UNLIKELY_START_SECTION "\n" \ + UNLIKELY_START_SECTION "\n\t" \ + SUBSECTION_LBL(unlikely) "\n" \ ".Lunlikely%=.tag:" #define UNLIKELY_END(tag) \ -- 2.39.5