From: Ard Biesheuvel <ardb@kernel.org>
Date: Wed, 17 Jun 2020 10:25:05 +0200
Subject: ACPI: tables: avoid relocations for table signature array
Patch-mainline: v5.9-rc1
Git-commit: 2229a12b64a4df7128b6e2d86be2688f8c76efec
References: jsc#SLE-16407

On architectures that implement KASLR using the ELF native RELA relocation
format (such as arm64), every absolute reference in the code incurs an
overhead of 24 bytes in the .rela section. So storing a 41 element array
of 4 character signature strings using an array of pointer-to-char incurs
an 8x overhead (32 bytes per entry => ~1500 bytes), and given the fixed
length of the entries, and the fact that the array is only used locally,
it is much better to use an array of arrays here, which gets rid of the
overhead entirely.

While at it, make it __initconst, as it is never referenced except from
__init code.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Lee, Chun-Yi <jlee@suse.com>
---
 drivers/acpi/tables.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -490,7 +490,7 @@ static u8 __init acpi_table_checksum(u8
 }
 
 /* All but ACPI_SIG_RSDP and ACPI_SIG_FACS: */
-static const char * const table_sigs[] = {
+static const char table_sigs[][ACPI_NAMESEG_SIZE] __initconst = {
 	ACPI_SIG_BERT, ACPI_SIG_BGRT, ACPI_SIG_CPEP, ACPI_SIG_ECDT,
 	ACPI_SIG_EINJ, ACPI_SIG_ERST, ACPI_SIG_HEST, ACPI_SIG_MADT,
 	ACPI_SIG_MSCT, ACPI_SIG_SBST, ACPI_SIG_SLIT, ACPI_SIG_SRAT,
@@ -501,7 +501,7 @@ static const char * const table_sigs[] =
 	ACPI_SIG_WDDT, ACPI_SIG_WDRT, ACPI_SIG_DSDT, ACPI_SIG_FADT,
 	ACPI_SIG_PSDT, ACPI_SIG_RSDT, ACPI_SIG_XSDT, ACPI_SIG_SSDT,
 	ACPI_SIG_IORT, ACPI_SIG_NFIT, ACPI_SIG_HMAT, ACPI_SIG_PPTT,
-	ACPI_SIG_NHLT, NULL };
+	ACPI_SIG_NHLT };
 
 #define ACPI_HEADER_SIZE sizeof(struct acpi_table_header)
 
@@ -548,11 +548,11 @@ void __init acpi_table_upgrade(void)
 
 		table = file.data;
 
-		for (sig = 0; table_sigs[sig]; sig++)
+		for (sig = 0; sig < ARRAY_SIZE(table_sigs); sig++)
 			if (!memcmp(table->signature, table_sigs[sig], 4))
 				break;
 
-		if (!table_sigs[sig]) {
+		if (sig >= ARRAY_SIZE(table_sigs)) {
 			pr_err("ACPI OVERRIDE: Unknown signature [%s%s]\n",
 				cpio_path, file.name);
 			continue;