linux-kernel - Re: [PATCH 1/2] tools/nolibc: add stdarg.h header

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Message-ID: <ZO2QC/fw6LKdtLSb@1wt.eu>
Date:   Tue, 29 Aug 2023 08:28:27 +0200
From:   Willy Tarreau <w@....eu>
To:     Thomas Weißschuh <linux@...ssschuh.net>
Cc:     Shuah Khan <shuah@...nel.org>, Zhangjin Wu <falcon@...ylab.org>,
        Yuan Tan <tanyuan@...ylab.org>, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 1/2] tools/nolibc: add stdarg.h header

Hi Thomas,

On Sun, Aug 27, 2023 at 10:00:15AM +0200, Thomas Weißschuh wrote:
> This allows nolic to work with `-nostdinc` avoiding any reliance on
> system headers.
> 
> The implementation has been lifted from musl libc 1.2.4.
> There is already an implementation of stdarg.h in include/linux/stdarg.h
> but that is GPL licensed and therefore not suitable for nolibc.

I'm a bit confused because for me, stdarg was normally provided by the
compiler, but I could be mistaken. It's just that it reminds me not so
old memories. Therefore maybe we just need to include or define
"something" to use it.

> +#ifndef _NOLIBC_STDARG_H
> +#define _NOLIBC_STDARG_H
> +
> +typedef __builtin_va_list va_list;
> +#define va_start(v, l)   __builtin_va_start(v, l)
> +#define va_end(v)        __builtin_va_end(v)
> +#define va_arg(v, l)     __builtin_va_arg(v, l)
> +#define va_copy(d, s)    __builtin_va_copy(d, s)
> +
> +#endif /* _NOLIBC_STDARG_H */

Also, regarding the doubt above, I really think these should be guarded
(maybe just use va_start as a hint), because the risk that they come
from libc headers or maybe from the compiler via another include path
is non-negligible.

Just my two cents,
Willy