[PATCH 5.15 1/5] arch: Introduce CONFIG_FUNCTION_ALIGNMENT

Thadeu Lima de Souza Cascardo
2024-03-13T10:43:24Z

From: Peter Zijlstra <peterz@infradead.org>

commit d49a0626216b95cd4bf696f6acf55f39a16ab0bb upstream.

Generic function-alignment infrastructure.

Architectures can select FUNCTION_ALIGNMENT_xxB symbols; the
FUNCTION_ALIGNMENT symbol is then set to the largest such selected
size, 0 otherwise.

From this the -falign-functions compiler argument and __ALIGN macro
are set.

This incorporates the DEBUG_FORCE_FUNCTION_ALIGN_64B knob and future
alignment requirements for x86_64 (later in this series) into a single
place.

NOTE: also removes the 0x90 filler byte from the generic __ALIGN
primitive, that value makes no sense outside of x86.

NOTE: .balign 0 reverts to a no-op.

Requested-by: Linus Torvalds <torvalds@linux-foundation.org>
Change-Id: I053b3c408d56988381feb8c8bdb5e27ea221755f
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111143.719248727@infradead.org
[cascardo: adjust context at arch/x86/Kconfig]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
---
Makefile | 4 ++--
arch/Kconfig | 24 ++++++++++++++++++++++++
arch/ia64/Kconfig | 1 +
arch/ia64/Makefile | 2 +-
arch/x86/Kconfig | 2 ++
arch/x86/boot/compressed/head_64.S | 8 ++++++++
arch/x86/include/asm/linkage.h | 4 +---
include/asm-generic/vmlinux.lds.h | 4 ++--
include/linux/linkage.h | 4 ++--
lib/Kconfig.debug | 1 +
10 files changed, 44 insertions(+), 10 deletions(-)

diff --git a/Makefile b/Makefile
index bb73dba0e505..16f3838838d0 100644
--- a/Makefile
+++ b/Makefile
@@ -1000,8 +1000,8 @@ 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
diff --git a/arch/Kconfig b/arch/Kconfig
index 2e2dc0975ab4..a541ce263865 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1303,4 +1303,28 @@ source "kernel/gcov/Kconfig"

source "scripts/gcc-plugins/Kconfig"

+config FUNCTION_ALIGNMENT_4B
+ bool
+
+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 4 if FUNCTION_ALIGNMENT_4B
+ default 0
+
endmenu
diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
index 89869aff8ca2..8902d1517894 100644
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -63,6 +63,7 @@ config IA64
select PCI_MSI_ARCH_FALLBACKS if PCI_MSI
select SET_FS
select ZONE_DMA32
+ select FUNCTION_ALIGNMENT_32B
default y
help
The Itanium Processor Family is Intel's 64-bit successor to
diff --git a/arch/ia64/Makefile b/arch/ia64/Makefile
index 7e548c654a29..43cde968da88 100644
--- 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)")
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index cfb1edd25437..65b2cff3c93b 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -267,6 +267,8 @@ config X86
select HAVE_ARCH_KCSAN if X86_64
select X86_FEATURE_NAMES if PROC_FS
select PROC_PID_ARCH_STATUS if PROC_FS
+ select FUNCTION_ALIGNMENT_16B if X86_64 || X86_ALIGNMENT_16
+ select FUNCTION_ALIGNMENT_4B
imply IMA_SECURE_AND_OR_TRUSTED_BOOT if EFI

config INSTRUCTION_DECODER
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index c3d427c817c7..e189a16ae40a 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -37,6 +37,14 @@
#include <asm/trapnr.h>
#include "pgtable.h"

+/*
+ * Fix alignment at 16 bytes. Following CONFIG_FUNCTION_ALIGNMENT will result
+ * in assembly errors due to trying to move .org backward due to the excessive
+ * alignment.
+ */
+#undef __ALIGN
+#define __ALIGN .balign 16, 0x90
+
/*
* Locally defined symbols should be marked hidden:
*/
diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
index 5000cf59bdf5..3d7293d52950 100644
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -13,10 +13,8 @@

#ifdef __ASSEMBLY__

-#if defined(CONFIG_X86_64) || defined(CONFIG_X86_ALIGNMENT_16)
-#define __ALIGN .p2align 4, 0x90
+#define __ALIGN .balign CONFIG_FUNCTION_ALIGNMENT, 0x90;
#define __ALIGN_STR __stringify(__ALIGN)
-#endif

#if defined(CONFIG_RETHUNK) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO)
#define RET jmp __x86_return_thunk
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 8471717c5085..dd9ea351bc02 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -81,8 +81,8 @@
#define RO_EXCEPTION_TABLE
#endif

-/* Align . to a 8 byte boundary equals to maximum function alignment. */
-#define ALIGN_FUNCTION() . = ALIGN(8)
+/* Align . function alignment. */
+#define ALIGN_FUNCTION() . = ALIGN(CONFIG_FUNCTION_ALIGNMENT)

/*
* LD_DEAD_CODE_DATA_ELIMINATION option enables -fdata-sections, which
diff --git a/include/linux/linkage.h b/include/linux/linkage.h
index dbf8506decca..fc81e51330b2 100644
--- 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__
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 64d6292cf686..28faea9b5da6 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -424,6 +424,7 @@ 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
--
2.34.1