Re: [RFC PATCH 4/6] selftests: fix build errors on alpine linux

[Pedro Falcato <pfalcato@suse.de>]

/me puts on his libc hat

On Thu, Aug 13, 2026 at 03:33:59PM +0900, Hajime Tazaki wrote:
> Some nommu architectures only work on Alpine Linux, which doesn't use
> glibc for the standard library.  It uses musl-libc and is implemented in
> a different way as glibc, resulting build failures.
> 
> This commit fixes this issue by adding missing definitions. The fixes
> are now only covered to TARGETS=mm which was tested for the moment;
> future contributions are needed to fully build/execute tests on nommu
> platforms.
> 
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: David Hildenbrand <david@kernel.org>
> Cc: Lorenzo Stoakes <ljs@kernel.org>
> Cc: "Liam R. Howlett" <liam@infradead.org>
> Cc: Vlastimil Babka <vbabka@kernel.org>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: Suren Baghdasaryan <surenb@google.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: linux-kselftest@vger.kernel.org
> Cc: linux-mm@kvack.org
> Cc: linux-um@lists.infradead.org
> Signed-off-by: Hajime Tazaki <thehajime@gmail.com>
> ---
>  tools/testing/selftests/kselftest.h      | 43 ++++++++++++++++++++++++
>  tools/testing/selftests/lib.mk           |  2 +-
>  tools/testing/selftests/mm/hugetlb_dio.c |  8 ++---
>  tools/testing/selftests/mm/mdwe_test.c   |  4 +--
>  4 files changed, 50 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/testing/selftests/kselftest.h b/tools/testing/selftests/kselftest.h
> index ae18c491ae53..ac21bf3d802e 100644
> --- a/tools/testing/selftests/kselftest.h
> +++ b/tools/testing/selftests/kselftest.h
> @@ -58,6 +58,7 @@
>  #include <string.h>
>  #include <stdio.h>
>  #include <sys/utsname.h>
> +#include <stdint.h>
>  #endif
>  
>  #ifndef ARRAY_SIZE
> @@ -81,6 +82,48 @@
>  #endif
>  #endif /* end arch */
>  
> +#if !defined(NOLIBC) && !defined(__GLIBC__)
> +#ifdef __LP64__
> +typedef int64_t __fsword_t;
> +#else
> +typedef int32_t __fsword_t;
> +#endif

The code should not be using __fsword_t. Per statfs(2):

       The __fsword_t type used for various fields in the statfs
       structure definition is a glibc internal type, not intended for
       public use.  This leaves the programmer in a bit of a conundrum
       when trying to copy or compare these fields to local variables in
       a program.  Using unsigned int for such variables suffices on most
       systems.

and indeed if you look at musl's statvfs definition:
struct statvfs {
	/* ... */
	unsigned int f_type;
	/* ... */
};

so it should be perfectly cromulent to use unsigned int here. Or use an
actual usable interface :)

> +
> +/*
> + * for a workaround to avoid struct conflict under
> + * musl-libc (<sys/prctl.h> v.s. <linux/prctl.h>)
> + */
> +#include <sys/prctl.h>
> +#ifndef _LINUX_PRCTL_H
> +#define _LINUX_PRCTL_H
> +#endif
> +
> +#ifndef PR_SET_MDWE
> +#define PR_SET_MDWE 65
> +#endif
> +
> +#ifndef PR_MDWE_REFUSE_EXEC_GAIN
> +#define PR_MDWE_REFUSE_EXEC_GAIN (1UL << 0)
> +#endif
> +
> +#ifndef PR_MDWE_NO_INHERIT
> +#define PR_MDWE_NO_INHERIT (1UL << 1)
> +#endif
> +
> +#ifndef PR_GET_MDWE
> +#define PR_GET_MDWE 66
> +#endif
> +
> +#ifndef PR_SET_MEMORY_MERGE
> +#define PR_SET_MEMORY_MERGE 67
> +#endif
> +
> +#ifndef PR_GET_MEMORY_MERGE
> +#define PR_GET_MEMORY_MERGE 68
> +#endif
> +
> +#endif

This looks fine. It's the same old problem with musl and kernel headers.

> +
>  /* define kselftest exit codes */
>  #define KSFT_PASS  0
>  #define KSFT_FAIL  1
> diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
> index f02cc8a2e4ae..2cc819006424 100644
> --- a/tools/testing/selftests/lib.mk
> +++ b/tools/testing/selftests/lib.mk
> @@ -197,7 +197,7 @@ clean: $(if $(TEST_GEN_MODS_DIR),clean_mods_dir)
>  	$(CLEAN)
>  
>  # Build with _GNU_SOURCE by default
> -CFLAGS += -D_GNU_SOURCE=
> +CFLAGS += -D_GNU_SOURCE= -D_LARGEFILE64_SOURCE

What needs this?

>  
>  # Additional include paths needed by kselftest.h and local headers
>  CFLAGS += -I${top_srcdir}/tools/testing/selftests
> diff --git a/tools/testing/selftests/mm/hugetlb_dio.c b/tools/testing/selftests/mm/hugetlb_dio.c
> index fb4600570e13..aee6be530ccb 100644
> --- a/tools/testing/selftests/mm/hugetlb_dio.c
> +++ b/tools/testing/selftests/mm/hugetlb_dio.c
> @@ -22,12 +22,9 @@
>  #include "kselftest.h"
>  #include "hugepage_settings.h"
>  
> -#ifndef STATX_DIOALIGN
> -#define STATX_DIOALIGN		0x00002000U
> -#endif

Why doesn't this fallback work?

> -
>  static int get_dio_alignment(int fd)
>  {
> +#ifdef STATX_DIOALIGN
>  	struct statx stx;
>  	int ret;
>  
> @@ -43,6 +40,9 @@ static int get_dio_alignment(int fd)
>  		return 1;
>  
>  	return stx.stx_dio_offset_align;
> +#else
> +	return -1;
> +#endif
>  }
>  
>  static bool check_dio_alignment(unsigned int start_off,
> diff --git a/tools/testing/selftests/mm/mdwe_test.c b/tools/testing/selftests/mm/mdwe_test.c
> index 647779653da0..031c79ed067e 100644
> --- a/tools/testing/selftests/mm/mdwe_test.c
> +++ b/tools/testing/selftests/mm/mdwe_test.c
> @@ -1,5 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0
>  
> +#include "kselftest_harness.h"
> +
>  #ifdef __aarch64__
>  #include <asm/hwcap.h>
>  #endif
> @@ -14,8 +16,6 @@
>  #include <sys/wait.h>
>  #include <unistd.h>
>  
> -#include "kselftest_harness.h"
> -
>  #ifndef __aarch64__
>  # define PROT_BTI	0
>  #endif
> -- 
> 2.43.0
> 
> 

Honestly, I'm surprised you needed so few hacks for this! But if I am to
guess, there are certainly much more problematic selftests out there.

-- 
Pedro