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

Hello Pedro,

thank you for the review and looking at the patch.

On Fri, 14 Aug 2026 18:34:21 +0900,
Pedro Falcato wrote:
> 
> /me puts on his libc hat

thanks, this is really a good news to me.

> > 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 :)

thanks, I will drop this chunk and propose to update mm/gup_longterm.c
to address the issue with musl.

> > +
> > +/*
> > + * 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.

noted with thanks.

> >  /* 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?

this is a leftover chunk of patch not for TARGETS=mm, but
TARGETS=drivers/dma-buf, which generates the following errors.

udmabuf.c:137:9: error: unknown type name 'off64_t'; did you mean 'off_t'?
  137 |         off64_t size;

I will drop this chunk from this patch as the patch is only focusing
on TARGETS=mm.

> >  
> >  # 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?

I thought that if this macro isn't defined, it's not available in the
underlying kernel, but that's very idiot modification given that the
libc headers is not up-to-date but the kernel is supporting this, this
ifndef should help.

I will look for another approach to address the situation of musl, and
revert this for the original purpose.

> > -
> >  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.

Currently I only tested with `TARGETS=mm` and didn't look carefully to
other tests.  I will look more into running other tests on alpine
(with CONFIG_MMU enabled) first, then will see !MMU environment with
investigating if those are meaningful to test on nommu.

anyway, (again) thanks for the review.

-- Hajime