[PATCH v3 43/64] x86/alternative: Define ELF section entry size for alternatives

[Josh Poimboeuf <jpoimboe@kernel.org>]

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

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/um/include/shared/common-offsets.h    | 2 ++
 arch/x86/include/asm/alternative.h         | 5 +++--
 arch/x86/include/asm/asm.h                 | 4 ++++
 arch/x86/kernel/asm-offsets.c              | 2 ++
 arch/x86/um/shared/sysdep/kernel-offsets.h | 1 +
 kernel/bounds.c                            | 1 +
 scripts/mod/devicetable-offsets.c          | 1 +
 7 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/um/include/shared/common-offsets.h b/arch/um/include/shared/common-offsets.h
index 8ca66a1918c3..4e19103afd71 100644
--- a/arch/um/include/shared/common-offsets.h
+++ b/arch/um/include/shared/common-offsets.h
@@ -18,3 +18,5 @@ DEFINE(UM_NSEC_PER_USEC, NSEC_PER_USEC);
 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));
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 15bc07a5ebb3..eb24d9ba30d7 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -197,7 +197,8 @@ static inline int alternatives_text_reserved(void *start, void *end)
 	"773:\n"
 
 #define ALTINSTR_ENTRY(ft_flags)					      \
-	".pushsection .altinstructions,\"a\"\n"				      \
+	".pushsection .altinstructions, \"aM\", @progbits, "		      \
+		      __stringify(ALT_INSTR_SIZE) "\n"			      \
 	" .long 771b - .\n"				/* label           */ \
 	" .long 774f - .\n"				/* new instruction */ \
 	" .4byte " __stringify(ft_flags) "\n"		/* feature + flags */ \
@@ -360,7 +361,7 @@ void nop_func(void);
 741:									\
 	.skip -(((744f-743f)-(741b-740b)) > 0) * ((744f-743f)-(741b-740b)),0x90	;\
 742:									\
-	.pushsection .altinstructions,"a" ;				\
+	.pushsection .altinstructions, "aM", @progbits, ALT_INSTR_SIZE ;\
 	altinstr_entry 740b,743f,flag,742b-740b,744f-743f ;		\
 	.popsection ;							\
 	.pushsection .altinstr_replacement,"ax"	;			\
diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index f963848024a5..1f26f90a57ce 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -136,6 +136,10 @@ static __always_inline __pure void *rip_rel_ptr(void *p)
 
 #ifdef __KERNEL__
 
+#ifndef COMPILE_OFFSETS
+#include <asm/asm-offsets.h>
+#endif
+
 # include <asm/extable_fixup_types.h>
 
 /* Exception table entry */
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 6259b474073b..b51625c3f64c 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -123,4 +123,6 @@ static void __used common(void)
 	OFFSET(ARIA_CTX_rounds, aria_ctx, rounds);
 #endif
 
+	BLANK();
+	DEFINE(ALT_INSTR_SIZE,	 sizeof(struct alt_instr));
 }
diff --git a/arch/x86/um/shared/sysdep/kernel-offsets.h b/arch/x86/um/shared/sysdep/kernel-offsets.h
index 6fd1ed400399..9f6d3d1a248c 100644
--- a/arch/x86/um/shared/sysdep/kernel-offsets.h
+++ b/arch/x86/um/shared/sysdep/kernel-offsets.h
@@ -1,4 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0 */
+#define COMPILE_OFFSETS
 #include <linux/stddef.h>
 #include <linux/sched.h>
 #include <linux/elf.h>
diff --git a/kernel/bounds.c b/kernel/bounds.c
index 29b2cd00df2c..02b619eb6106 100644
--- a/kernel/bounds.c
+++ b/kernel/bounds.c
@@ -6,6 +6,7 @@
  */
 
 #define __GENERATING_BOUNDS_H
+#define COMPILE_OFFSETS
 /* Include headers that define the enum constants of interest */
 #include <linux/page-flags.h>
 #include <linux/mmzone.h>
diff --git a/scripts/mod/devicetable-offsets.c b/scripts/mod/devicetable-offsets.c
index d3d00e85edf7..ef2ffb68f69d 100644
--- a/scripts/mod/devicetable-offsets.c
+++ b/scripts/mod/devicetable-offsets.c
@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
+#define COMPILE_OFFSETS
 #include <linux/kbuild.h>
 #include <linux/mod_devicetable.h>
 
-- 
2.49.0