linux-kernel - [PATCH v2 45/62] x86/extable: Define ELF section entry size for exception tables

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Message-ID: <198cfbd12e54dfce1309828e146b90b1f7b200a5.1746821544.git.jpoimboe@kernel.org>
Date: Fri,  9 May 2025 13:17:09 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	Petr Mladek <pmladek@...e.com>,
	Miroslav Benes <mbenes@...e.cz>,
	Joe Lawrence <joe.lawrence@...hat.com>,
	live-patching@...r.kernel.org,
	Song Liu <song@...nel.org>,
	laokz <laokz@...mail.com>,
	Jiri Kosina <jikos@...nel.org>,
	Marcos Paulo de Souza <mpdesouza@...e.com>,
	Weinan Liu <wnliu@...gle.com>,
	Fazla Mehrab <a.mehrab@...edance.com>,
	Chen Zhongjin <chenzhongjin@...wei.com>,
	Puranjay Mohan <puranjay@...nel.org>
Subject: [PATCH v2 45/62] x86/extable: Define ELF section entry size for exception tables

In preparation for the objtool klp diff subcommand, define the entry
size for the __ex_table section in its ELF header.  This will allow
tooling to extract individual entries.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 arch/x86/include/asm/asm.h | 20 ++++++++++++--------
 kernel/extable.c           |  2 ++
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index f963848024a5..62dff336f206 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -138,15 +138,17 @@ static __always_inline __pure void *rip_rel_ptr(void *p)
 
 # include <asm/extable_fixup_types.h>
 
+#define EXTABLE_SIZE 12
+
 /* Exception table entry */
 #ifdef __ASSEMBLER__
 
-# define _ASM_EXTABLE_TYPE(from, to, type)			\
-	.pushsection "__ex_table","a" ;				\
-	.balign 4 ;						\
-	.long (from) - . ;					\
-	.long (to) - . ;					\
-	.long type ;						\
+# define _ASM_EXTABLE_TYPE(from, to, type)				\
+	.pushsection "__ex_table", "aM", @progbits, EXTABLE_SIZE;	\
+	.balign 4 ;							\
+	.long (from) - . ;						\
+	.long (to) - . ;						\
+	.long type ;							\
 	.popsection
 
 # ifdef CONFIG_KPROBES
@@ -189,7 +191,8 @@ static __always_inline __pure void *rip_rel_ptr(void *p)
 	".purgem extable_type_reg\n"
 
 # define _ASM_EXTABLE_TYPE(from, to, type)			\
-	" .pushsection \"__ex_table\",\"a\"\n"			\
+	" .pushsection __ex_table, \"aM\", @progbits, "		\
+		       __stringify(EXTABLE_SIZE) "\n"		\
 	" .balign 4\n"						\
 	" .long (" #from ") - .\n"				\
 	" .long (" #to ") - .\n"				\
@@ -197,7 +200,8 @@ static __always_inline __pure void *rip_rel_ptr(void *p)
 	" .popsection\n"
 
 # define _ASM_EXTABLE_TYPE_REG(from, to, type, reg)				\
-	" .pushsection \"__ex_table\",\"a\"\n"					\
+	" .pushsection __ex_table, \"aM\", @progbits, "				\
+		       __stringify(EXTABLE_SIZE) "\n"				\
 	" .balign 4\n"								\
 	" .long (" #from ") - .\n"						\
 	" .long (" #to ") - .\n"						\
diff --git a/kernel/extable.c b/kernel/extable.c
index 71f482581cab..0ae3ee2ef266 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -55,6 +55,8 @@ const struct exception_table_entry *search_exception_tables(unsigned long addr)
 {
 	const struct exception_table_entry *e;
 
+	BUILD_BUG_ON(EXTABLE_SIZE != sizeof(struct exception_table_entry));
+
 	e = search_kernel_exception_table(addr);
 	if (!e)
 		e = search_module_extables(addr);
-- 
2.49.0