Re: [PATCH v9 2/5] x86/asm, x86/boot: expose inline memcmp()

[H. Peter Anvin]

On September 6, 2026 10:01:16 AM PDT, Borislav Petkov <bp@xxxxxxxxx> wrote:
>On Sat, Aug 22, 2026 at 03:33:18PM -0300, Mauricio Faria de Oliveira wrote:
>> Move the inline memcmp function currently only available in 'boot/string.c'
>> into the shared string function header <asm/shared/string.h> to be reused.
>> 
>> This is not done through <asm/string.h> to avoid pulling unnecessary code
>> in 'boot/string.c' that causes build errors in 'boot/compressed/string.c'
>> and 'purgatory/purgatory.ro'.
>
>Please drop those '' quotes - it is perfectly clear that those are .c files.
>
>> No functional changes.
>> 
>> Signed-off-by: Mauricio Faria de Oliveira <mfo@xxxxxxxxxx>
>> 
>> ---
>> 
>> Thanks to David Laight for noticing the return value difference between
>> inline and regular memcmp().
>> ---
>>  arch/x86/boot/string.c               | 13 ++-----------
>>  arch/x86/include/asm/shared/string.h | 26 ++++++++++++++++++++++++++
>>  2 files changed, 28 insertions(+), 11 deletions(-)
>
>...
>
>> diff --git a/arch/x86/include/asm/shared/string.h b/arch/x86/include/asm/shared/string.h
>> new file mode 100644
>> index 0000000000000000000000000000000000000000..06c1d5e5013e4d59cfb49866d10e164362d2c4cc
>> --- /dev/null
>> +++ b/arch/x86/include/asm/shared/string.h
>> @@ -0,0 +1,26 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#ifndef _ASM_X86_SHARED_STRING_H
>> +#define _ASM_X86_SHARED_STRING_H
>> +
>> +/*
>> + * This inline memcmp() returns 0 (equal) or 1 (not equal).
>> + * The regular memcmp() returns <0 (less than), 0 (equal), or >0 (greater than)
>> + * to indicate ordering as well.
>
>No need to overdo it:
>
>	Returns:	0 (equal)
>			1 (not equal)
>
>In contrast, the regular memcmp() follows glibc return value semantics.
>
>

Worth noting that memeq() and streq() are becoming used in other contexts, e.g. glibc.