linux-kernel - [PATCH v3 46/64] x86/extable: Define ELF section entry size for exception table

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Message-ID: <1a53b6dcf236ce1fe0f0cd0d4441fc2bd9022cb3.1750980517.git.jpoimboe@kernel.org>
Date: Thu, 26 Jun 2025 16:55:33 -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>,
	Dylan Hatch <dylanbhatch@...gle.com>
Subject: [PATCH v3 46/64] x86/extable: Define ELF section entry size for exception table

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/um/include/asm/Kbuild                 |  1 -
 arch/um/include/shared/common-offsets.h    |  1 +
 arch/x86/include/asm/asm.h                 | 18 ++++++++++--------
 arch/x86/kernel/asm-offsets.c              |  1 +
 arch/x86/um/shared/sysdep/kernel-offsets.h |  1 +
 5 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/arch/um/include/asm/Kbuild b/arch/um/include/asm/Kbuild
index 04ab3b653a48..1934fa0df888 100644
--- a/arch/um/include/asm/Kbuild
+++ b/arch/um/include/asm/Kbuild
@@ -5,7 +5,6 @@ generic-y += device.h
 generic-y += dma-mapping.h
 generic-y += emergency-restart.h
 generic-y += exec.h
-generic-y += extable.h
 generic-y += ftrace.h
 generic-y += hw_irq.h
 generic-y += irq_regs.h
diff --git a/arch/um/include/shared/common-offsets.h b/arch/um/include/shared/common-offsets.h
index 4e19103afd71..a6f77cb6aa7e 100644
--- a/arch/um/include/shared/common-offsets.h
+++ b/arch/um/include/shared/common-offsets.h
@@ -20,3 +20,4 @@ DEFINE(UM_KERN_GDT_ENTRY_TLS_ENTRIES, GDT_ENTRY_TLS_ENTRIES);
 DEFINE(UM_SECCOMP_ARCH_NATIVE, SECCOMP_ARCH_NATIVE);
 
 DEFINE(ALT_INSTR_SIZE, sizeof(struct alt_instr));
+DEFINE(EXTABLE_SIZE,   sizeof(struct exception_table_entry));
diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 1f26f90a57ce..e9b6d2d006c6 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -145,12 +145,12 @@ static __always_inline __pure void *rip_rel_ptr(void *p)
 /* 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
@@ -193,7 +193,8 @@ 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"				\
@@ -201,7 +202,8 @@ 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/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index b51625c3f64c..3d3eef7fae32 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -125,4 +125,5 @@ static void __used common(void)
 
 	BLANK();
 	DEFINE(ALT_INSTR_SIZE,	 sizeof(struct alt_instr));
+	DEFINE(EXTABLE_SIZE,	 sizeof(struct exception_table_entry));
 }
diff --git a/arch/x86/um/shared/sysdep/kernel-offsets.h b/arch/x86/um/shared/sysdep/kernel-offsets.h
index 9f6d3d1a248c..8215a0200ddd 100644
--- a/arch/x86/um/shared/sysdep/kernel-offsets.h
+++ b/arch/x86/um/shared/sysdep/kernel-offsets.h
@@ -8,6 +8,7 @@
 #include <linux/audit.h>
 #include <asm/mman.h>
 #include <asm/seccomp.h>
+#include <asm/extable.h>
 
 /* workaround for a warning with -Wmissing-prototypes */
 void foo(void);
-- 
2.49.0