Move the inline memcmp function, currently only available to boot code
(boot/string.c), into the header with similar inline string functions
(include/asm/string.h) so it may be reused.

Add a _SETUP guard in string.h so not to include the 32/64-bit specific
string headers in boot/ code (16-bit, real mode) and avoid build errors.

Signed-off-by: Mauricio Faria de Oliveira <mfo@igalia.com>
---
 arch/x86/boot/string.c        |  6 ++----
 arch/x86/include/asm/string.h | 11 +++++++++++
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
index b25c6a9303b7314d5caf5c9306239811705294fe..bbee78637b349e42e9281d8df50d89d48f4490b9 100644
--- a/arch/x86/boot/string.c
+++ b/arch/x86/boot/string.c
@@ -15,6 +15,7 @@
 #include <linux/errno.h>
 #include <linux/limits.h>
 #include <asm/asm.h>
+#include <asm/string.h>
 #include "ctype.h"
 #include "string.h"
 
@@ -31,10 +32,7 @@
 
 int memcmp(const void *s1, const void *s2, size_t len)
 {
-	bool diff;
-	asm("repe cmpsb"
-	    : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));
-	return diff;
+	return __inline_memcmp(s1, s2, len);
 }
 
 /*
diff --git a/arch/x86/include/asm/string.h b/arch/x86/include/asm/string.h
index 9cb5aae7fba9ffcf0f5af8f939d30467750ccaa9..736a6f6a31f0a68281b4f17415aba0fcd95dc228 100644
--- a/arch/x86/include/asm/string.h
+++ b/arch/x86/include/asm/string.h
@@ -2,11 +2,13 @@
 #ifndef _ASM_X86_STRING_H
 #define _ASM_X86_STRING_H
 
+#ifndef _SETUP
 #ifdef CONFIG_X86_32
 # include <asm/string_32.h>
 #else
 # include <asm/string_64.h>
 #endif
+#endif
 
 static __always_inline void *__inline_memcpy(void *to, const void *from, size_t len)
 {
@@ -29,4 +31,13 @@ static __always_inline void *__inline_memset(void *s, int v, size_t n)
 	return ret;
 }
 
+static __always_inline int __inline_memcmp(const void *s1, const void *s2, size_t len)
+{
+	bool diff;
+
+	asm("repe cmpsb"
+	    : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));
+	return diff;
+}
+
 #endif /* _ASM_X86_STRING_H */

-- 
2.51.0

On Wed, 22 Apr 2026 17:07:45 -0300
Mauricio Faria de Oliveira <mfo@igalia.com> wrote:

> Move the inline memcmp function, currently only available to boot code
> (boot/string.c), into the header with similar inline string functions
> (include/asm/string.h) so it may be reused.

This needs a comment/warning that it is incompatible with normal memcmp()
because it only returns 0/1 not -1/0/1.
Most callers don't care.

	David


> 
> Add a _SETUP guard in string.h so not to include the 32/64-bit specific
> string headers in boot/ code (16-bit, real mode) and avoid build errors.
> 
> Signed-off-by: Mauricio Faria de Oliveira <mfo@igalia.com>
> ---
>  arch/x86/boot/string.c        |  6 ++----
>  arch/x86/include/asm/string.h | 11 +++++++++++
>  2 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
> index b25c6a9303b7314d5caf5c9306239811705294fe..bbee78637b349e42e9281d8df50d89d48f4490b9 100644
> --- a/arch/x86/boot/string.c
> +++ b/arch/x86/boot/string.c
> @@ -15,6 +15,7 @@
>  #include <linux/errno.h>
>  #include <linux/limits.h>
>  #include <asm/asm.h>
> +#include <asm/string.h>
>  #include "ctype.h"
>  #include "string.h"
>  
> @@ -31,10 +32,7 @@
>  
>  int memcmp(const void *s1, const void *s2, size_t len)
>  {
> -	bool diff;
> -	asm("repe cmpsb"
> -	    : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));
> -	return diff;
> +	return __inline_memcmp(s1, s2, len);
>  }
>  
>  /*
> diff --git a/arch/x86/include/asm/string.h b/arch/x86/include/asm/string.h
> index 9cb5aae7fba9ffcf0f5af8f939d30467750ccaa9..736a6f6a31f0a68281b4f17415aba0fcd95dc228 100644
> --- a/arch/x86/include/asm/string.h
> +++ b/arch/x86/include/asm/string.h
> @@ -2,11 +2,13 @@
>  #ifndef _ASM_X86_STRING_H
>  #define _ASM_X86_STRING_H
>  
> +#ifndef _SETUP
>  #ifdef CONFIG_X86_32
>  # include <asm/string_32.h>
>  #else
>  # include <asm/string_64.h>
>  #endif
> +#endif
>  
>  static __always_inline void *__inline_memcpy(void *to, const void *from, size_t len)
>  {
> @@ -29,4 +31,13 @@ static __always_inline void *__inline_memset(void *s, int v, size_t n)
>  	return ret;
>  }
>  
> +static __always_inline int __inline_memcmp(const void *s1, const void *s2, size_t len)
> +{
> +	bool diff;
> +
> +	asm("repe cmpsb"
> +	    : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));
> +	return diff;
> +}
> +
>  #endif /* _ASM_X86_STRING_H */
>

On 2026-04-22 17:54, David Laight wrote:
> On Wed, 22 Apr 2026 17:07:45 -0300
> Mauricio Faria de Oliveira <mfo@igalia.com> wrote:
> 
>> Move the inline memcmp function, currently only available to boot code
>> (boot/string.c), into the header with similar inline string functions
>> (include/asm/string.h) so it may be reused.
> 
> This needs a comment/warning that it is incompatible with normal memcmp()
> because it only returns 0/1 not -1/0/1.
> Most callers don't care.

Thanks for catching and suggesting this.

I can also change it to -1/0/1 in a later patch, to keep v2 only a fix
and split a behavior change, with something like this (lightly tested):

static __always_inline int __inline_memcmp(const void *s1, const void
*s2, size_t len)
{
        bool above, below;

        asm("repe cmpsb"
            : "+S" (s1), "+D" (s2), "+c" (len),
              "=@cca" (above),
              "=@ccb" (below));

        return above - below;
}

cheers,

> 
> 	David
> 
> 
>> 
>> Add a _SETUP guard in string.h so not to include the 32/64-bit specific
>> string headers in boot/ code (16-bit, real mode) and avoid build errors.
>> 
>> Signed-off-by: Mauricio Faria de Oliveira <mfo@igalia.com>
>> ---
>>  arch/x86/boot/string.c        |  6 ++----
>>  arch/x86/include/asm/string.h | 11 +++++++++++
>>  2 files changed, 13 insertions(+), 4 deletions(-)
>> 
>> diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
>> index b25c6a9303b7314d5caf5c9306239811705294fe..bbee78637b349e42e9281d8df50d89d48f4490b9 100644
>> --- a/arch/x86/boot/string.c
>> +++ b/arch/x86/boot/string.c
>> @@ -15,6 +15,7 @@
>>  #include <linux/errno.h>
>>  #include <linux/limits.h>
>>  #include <asm/asm.h>
>> +#include <asm/string.h>
>>  #include "ctype.h"
>>  #include "string.h"
>>  
>> @@ -31,10 +32,7 @@
>>  
>>  int memcmp(const void *s1, const void *s2, size_t len)
>>  {
>> -	bool diff;
>> -	asm("repe cmpsb"
>> -	    : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));
>> -	return diff;
>> +	return __inline_memcmp(s1, s2, len);
>>  }
>>  
>>  /*
>> diff --git a/arch/x86/include/asm/string.h b/arch/x86/include/asm/string.h
>> index 9cb5aae7fba9ffcf0f5af8f939d30467750ccaa9..736a6f6a31f0a68281b4f17415aba0fcd95dc228 100644
>> --- a/arch/x86/include/asm/string.h
>> +++ b/arch/x86/include/asm/string.h
>> @@ -2,11 +2,13 @@
>>  #ifndef _ASM_X86_STRING_H
>>  #define _ASM_X86_STRING_H
>>  
>> +#ifndef _SETUP
>>  #ifdef CONFIG_X86_32
>>  # include <asm/string_32.h>
>>  #else
>>  # include <asm/string_64.h>
>>  #endif
>> +#endif
>>  
>>  static __always_inline void *__inline_memcpy(void *to, const void *from, size_t len)
>>  {
>> @@ -29,4 +31,13 @@ static __always_inline void *__inline_memset(void *s, int v, size_t n)
>>  	return ret;
>>  }
>>  
>> +static __always_inline int __inline_memcmp(const void *s1, const void *s2, size_t len)
>> +{
>> +	bool diff;
>> +
>> +	asm("repe cmpsb"
>> +	    : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));
>> +	return diff;
>> +}
>> +
>>  #endif /* _ASM_X86_STRING_H */
>>

-- 
Mauricio