linux-kernel - Re: [PATCH v3 1/3] tools headers: Go back to include asm-generic/unistd.h for arm64

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Message-ID: <58e432e4-5825-4f2e-9aba-29be63eac56f@linaro.org>
Date: Wed, 24 Dec 2025 13:47:51 +0000
From: James Clark <james.clark@...aro.org>
To: Leo Yan <leo.yan@....com>, Arnd Bergmann <arnd@...db.de>
Cc: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
 Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH v3 1/3] tools headers: Go back to include
 asm-generic/unistd.h for arm64



On 22/12/2025 6:06 pm, Leo Yan wrote:
> The header unistd.h is included under Arm64's uAPI folder (see
> tools/arch/arm64/include/uapi/asm/), but it does not include its
> dependent header unistd_64.h.  The intention is for unistd_64.h to be
> generated dynamically using scripts/Makefile.asm-headers.
> 
> However, this dynamic approach causes problems because the header is not
> available early enough, even though it is widely included throughout
> tools.  Using the perf build as an example:
> 
>   1) Feature detection: Perf first runs feature tests.
> 
>      The BPF feature program test-bpf.c includes unistd.h.  Since
>      unistd_64.h has not been generated yet, the program fails to build,
>      and the BPF feature ends up being disabled.
> 
>   2) libperf build:
> 
>      The libperf Makefile later generates unistd_64.h on the fly, so
>      libperf itself builds successfully.
> 
>   3) Final perf build:
> 
>      Although the perf binary can build successfully using the generated
>      header, we never get a chance to build BPF skeleton programs,
>      because BPF support was already disabled earlier.
> 
> To fix the issue, it restores to include asm-generic/unistd.h.  This is

Would this prevent us from using any Arm64 specific syscalls in the 
future? I think that's a downside of this approach vs copying the 
generated output that should be noted here.

> consistent with other architectures and ensures the header is available

'Consistent' isn't accurate is it? x86 already has static copies of 
syscalls in tools/arch/x86/include/uapi/asm/unistd_32.h and 
tools/arch/x86/include/uapi/asm/unistd_64.h.

Maybe something more like "eventual consistency" is intended, if we plan 
to remove those x86 headers too? I'm still a bit lost about why Arm64 
copying the generated header is considered a special case when we 
already have these x86 ones.

> from the start.
> 
> Fixes: 22f72088ffe6 ("tools headers: Update the syscall table with the kernel sources")
> Signed-off-by: Leo Yan <leo.yan@....com>
> ---
>   tools/arch/arm64/include/uapi/asm/unistd.h | 24 +++++++++++++++++++++++-
>   1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/arch/arm64/include/uapi/asm/unistd.h b/tools/arch/arm64/include/uapi/asm/unistd.h
> index df36f23876e863ff0a9e88473d5339f7ab69516d..9306726337fe005e3cf3e1ffd38dc6356191fa95 100644
> --- a/tools/arch/arm64/include/uapi/asm/unistd.h
> +++ b/tools/arch/arm64/include/uapi/asm/unistd.h
> @@ -1,2 +1,24 @@
>   /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> -#include <asm/unistd_64.h>
> +/*
> + * Copyright (C) 2012 ARM Ltd.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#define __ARCH_WANT_RENAMEAT
> +#define __ARCH_WANT_NEW_STAT
> +#define __ARCH_WANT_SET_GET_RLIMIT
> +#define __ARCH_WANT_TIME32_SYSCALLS
> +#define __ARCH_WANT_MEMFD_SECRET
> +
> +#include <asm-generic/unistd.h>
>