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Message-ID: <YxXJswK9QjhCGmPN@hirez.programming.kicks-ass.net>
Date: Mon, 5 Sep 2022 12:04:35 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
x86@...nel.org, Tim Chen <tim.c.chen@...ux.intel.com>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Andrew Cooper <Andrew.Cooper3@...rix.com>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Johannes Wikner <kwikner@...z.ch>,
Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
Jann Horn <jannh@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>,
Joao Moreira <joao.moreira@...el.com>,
Joseph Nuzman <joseph.nuzman@...el.com>,
Steven Rostedt <rostedt@...dmis.org>,
Juergen Gross <jgross@...e.com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
K Prateek Nayak <kprateek.nayak@....com>,
Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH v2 08/59] x86/build: Ensure proper function alignment
On Fri, Sep 02, 2022 at 11:08:54AM -0700, Linus Torvalds wrote:
> Let's just do this right.
Something like so then?
---
--- a/Makefile
+++ b/Makefile
@@ -940,8 +940,8 @@ KBUILD_CFLAGS += $(CC_FLAGS_CFI)
export CC_FLAGS_CFI
endif
-ifdef CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_64B
-KBUILD_CFLAGS += -falign-functions=64
+ifneq ($(CONFIG_FUNCTION_ALIGNMENT),0)
+KBUILD_CFLAGS += -falign-functions=$(CONFIG_FUNCTION_ALIGNMENT)
endif
# arch Makefile may override CC so keep this after arch Makefile is included
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1419,4 +1419,24 @@ source "kernel/gcov/Kconfig"
source "scripts/gcc-plugins/Kconfig"
+config FUNCTION_ALIGNMENT_8B
+ bool
+
+config FUNCTION_ALIGNMENT_16B
+ bool
+
+config FUNCTION_ALIGNMENT_32B
+ bool
+
+config FUNCTION_ALIGNMENT_64B
+ bool
+
+config FUNCTION_ALIGNMENT
+ int
+ default 64 if FUNCTION_ALIGNMENT_64B
+ default 32 if FUNCTION_ALIGNMENT_32B
+ default 16 if FUNCTION_ALIGNMENT_16B
+ default 8 if FUNCTION_ALIGNMENT_8B
+ default 0
+
endmenu
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -63,6 +63,7 @@ config IA64
select NUMA if !FLATMEM
select PCI_MSI_ARCH_FALLBACKS if PCI_MSI
select ZONE_DMA32
+ select FUNCTION_ALIGNMENT_32B
default y
help
The Itanium Processor Family is Intel's 64-bit successor to
--- a/arch/ia64/Makefile
+++ b/arch/ia64/Makefile
@@ -23,7 +23,7 @@ KBUILD_AFLAGS_KERNEL := -mconstant-gp
EXTRA :=
cflags-y := -pipe $(EXTRA) -ffixed-r13 -mfixed-range=f12-f15,f32-f127 \
- -falign-functions=32 -frename-registers -fno-optimize-sibling-calls
+ -frename-registers -fno-optimize-sibling-calls
KBUILD_CFLAGS_KERNEL := -mconstant-gp
GAS_STATUS = $(shell $(srctree)/arch/ia64/scripts/check-gas "$(CC)" "$(OBJDUMP)")
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -283,6 +283,8 @@ config X86
select X86_FEATURE_NAMES if PROC_FS
select PROC_PID_ARCH_STATUS if PROC_FS
select HAVE_ARCH_NODE_DEV_GROUP if X86_SGX
+ select FUNCTION_ALIGNMENT_16B if X86_64 || X86_ALIGNMENT_16
+ select FUNCTION_ALIGNMENT_8B
imply IMA_SECURE_AND_OR_TRUSTED_BOOT if EFI
config INSTRUCTION_DECODER
@@ -2442,6 +2444,7 @@ config HAVE_CALL_THUNKS
depends on CC_HAS_ENTRY_PADDING && RETHUNK && OBJTOOL
config CALL_THUNKS
+ select FUNCTION_ALIGNMENT_16B
def_bool n
menuconfig SPECULATION_MITIGATIONS
@@ -2515,6 +2518,7 @@ config CALL_DEPTH_TRACKING
config CALL_THUNKS_DEBUG
bool "Enable call thunks and call depth tracking debugging"
+ select FUNCTION_ALIGNMENT_32B
depends on CALL_DEPTH_TRACKING
default n
help
--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -517,9 +517,3 @@ config CPU_SUP_VORTEX_32
makes the kernel a tiny bit smaller.
If unsure, say N.
-
-# Defined here so it is defined for UM too
-config FUNCTION_ALIGNMENT
- int
- default 16 if X86_64 || X86_ALIGNMENT_16
- default 8
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -84,10 +84,6 @@ else
KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none)
endif
-ifneq ($(CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_64B),y)
-KBUILD_CFLAGS += -falign-functions=$(CONFIG_FUNCTION_ALIGNMENT)
-endif
-
ifeq ($(CONFIG_X86_32),y)
BITS := 32
UTS_MACHINE := i386
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -12,16 +12,7 @@
#define asmlinkage CPP_ASMLINKAGE __attribute__((regparm(0)))
#endif /* CONFIG_X86_32 */
-#if CONFIG_FUNCTION_ALIGNMENT == 8
-# define __ALIGN .p2align 3, 0x90;
-#elif CONFIG_FUNCTION_ALIGNMENT == 16
-# define __ALIGN .p2align 4, 0x90;
-#elif CONFIG_FUNCTION_ALIGNMENT == 32
-# define __ALIGN .p2align 5, 0x90
-#else
-# error Unsupported function alignment
-#endif
-
+#define __ALIGN .balign CONFIG_FUNCTION_ALIGNMENT, 0x90
#define __ALIGN_STR __stringify(__ALIGN)
#ifdef CONFIG_CFI_CLANG
--- a/include/linux/linkage.h
+++ b/include/linux/linkage.h
@@ -69,8 +69,8 @@
#endif
#ifndef __ALIGN
-#define __ALIGN .align 4,0x90
-#define __ALIGN_STR ".align 4,0x90"
+#define __ALIGN .balign CONFIG_FUNCTION_ALIGNMENT
+#define __ALIGN_STR __stringify(__ALIGN)
#endif
#ifdef __ASSEMBLY__
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -459,6 +459,7 @@ config SECTION_MISMATCH_WARN_ONLY
config DEBUG_FORCE_FUNCTION_ALIGN_64B
bool "Force all function address 64B aligned"
depends on EXPERT && (X86_64 || ARM64 || PPC32 || PPC64 || ARC)
+ select FUNCTION_ALIGNMENT_64B
help
There are cases that a commit from one domain changes the function
address alignment of other domains, and cause magic performance
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