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Date:   Tue, 22 Feb 2022 16:01:27 +0300
From:   Alexey Dobriyan <adobriyan@gmail.com>
To:     tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, hpa@zytor.com
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] x86, alternative: record .altinstructions section entity size
Message-ID: <YhTep9uK8kLdTOsY@localhost.localdomain>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
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Precedence: bulk

.altinstructions entry was 12 bytes in size, then it was 13 bytes,
now it is 12 again. Record this information as section sh_entsize value
so that tools which parse .altinstructions have easier time.

Dividing section size by 12 or 13 and looking at the remainder doesn't
work because the number of alternative entries itself can be multiple of
entry size.

Signed-off-by: Alexey Dobriyan (CloudLinux) <adobriyan@gmail.com>
---

 arch/x86/include/asm/alternative.h |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -9,6 +9,8 @@
 #define ALTINSTR_FLAG_INV	(1 << 15)
 #define ALT_NOT(feat)		((feat) | ALTINSTR_FLAG_INV)
 
+#define sizeof_struct_alt_instr 12
+
 #ifndef __ASSEMBLY__
 
 #include <linux/stddef.h>
@@ -66,6 +68,7 @@ struct alt_instr {
 	u8  instrlen;		/* length of original instruction */
 	u8  replacementlen;	/* length of new instruction */
 } __packed;
+_Static_assert(sizeof(struct alt_instr) == sizeof_struct_alt_instr);
 
 /*
  * Debug flag that can be tested to see whether alternative
@@ -159,7 +162,7 @@ static inline int alternatives_text_reserved(void *start, void *end)
 /* alternative assembly primitive: */
 #define ALTERNATIVE(oldinstr, newinstr, feature)			\
 	OLDINSTR(oldinstr, 1)						\
-	".pushsection .altinstructions,\"a\"\n"				\
+	".pushsection .altinstructions,\"aM\",@progbits," __stringify(sizeof_struct_alt_instr) "\n"\
 	ALTINSTR_ENTRY(feature, 1)					\
 	".popsection\n"							\
 	".pushsection .altinstr_replacement, \"ax\"\n"			\
@@ -168,7 +171,7 @@ static inline int alternatives_text_reserved(void *start, void *end)
 
 #define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
 	OLDINSTR_2(oldinstr, 1, 2)					\
-	".pushsection .altinstructions,\"a\"\n"				\
+	".pushsection .altinstructions,\"aM\",@progbits," __stringify(sizeof_struct_alt_instr) "\n"\
 	ALTINSTR_ENTRY(feature1, 1)					\
 	ALTINSTR_ENTRY(feature2, 2)					\
 	".popsection\n"							\
@@ -184,7 +187,7 @@ static inline int alternatives_text_reserved(void *start, void *end)
 
 #define ALTERNATIVE_3(oldinsn, newinsn1, feat1, newinsn2, feat2, newinsn3, feat3) \
 	OLDINSTR_3(oldinsn, 1, 2, 3)						\
-	".pushsection .altinstructions,\"a\"\n"					\
+	".pushsection .altinstructions,\"aM\",@progbits," __stringify(sizeof_struct_alt_instr) "\n"\
 	ALTINSTR_ENTRY(feat1, 1)						\
 	ALTINSTR_ENTRY(feat2, 2)						\
 	ALTINSTR_ENTRY(feat3, 3)						\
@@ -331,7 +334,7 @@ static inline int alternatives_text_reserved(void *start, void *end)
 	.skip -(((144f-143f)-(141b-140b)) > 0) * ((144f-143f)-(141b-140b)),0x90
 142:
 
-	.pushsection .altinstructions,"a"
+	.pushsection .altinstructions,"aM",@progbits,sizeof_struct_alt_instr
 	altinstruction_entry 140b,143f,\feature,142b-140b,144f-143f
 	.popsection
 
@@ -368,7 +371,7 @@ static inline int alternatives_text_reserved(void *start, void *end)
 		(alt_max_short(new_len1, new_len2) - (old_len)),0x90
 142:
 
-	.pushsection .altinstructions,"a"
+	.pushsection .altinstructions,"aM",@progbits,sizeof_struct_alt_instr
 	altinstruction_entry 140b,143f,\feature1,142b-140b,144f-143f
 	altinstruction_entry 140b,144f,\feature2,142b-140b,145f-144f
 	.popsection