linux-kernel - Re: [RFC PATCH 2/9] tools/nolibc: crt: Split _start

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Message-ID: <af74dec4-7d32-4a3c-9624-d4e2138241c5@t-8ch.de>
Date: Sun, 1 Feb 2026 17:33:20 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Daniel Palmer <daniel@...ngy.jp>
Cc: w@....eu, kees@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/9] tools/nolibc: crt: Split _start_c() into
 stack-only and normal part

On 2026-01-31 16:44:33+0900, Daniel Palmer wrote:
> To prepare for nolibc programs being able to relocate themselves
> we need to split _start_c() into two parts:
> 
> - One part that only uses the stack so there are no accesses via
>   the GOT etc that isn't setup yet. Note that on m68k at least
>   this also means forcing the stackprotector off because accessing
>   the stack protector canary is done via the GOT.
> 
> - Another part that is called after we have done relocation so it
>   is safe to access global variables etc that might use the GOT etc.
> 
> Signed-off-by: Daniel Palmer <daniel@...ngy.jp>
> ---
>  tools/include/nolibc/crt.h | 57 +++++++++++++++++++++++---------------
>  1 file changed, 35 insertions(+), 22 deletions(-)
> 
> diff --git a/tools/include/nolibc/crt.h b/tools/include/nolibc/crt.h
> index d9262998dae9..899062c00fb7 100644
> --- a/tools/include/nolibc/crt.h
> +++ b/tools/include/nolibc/crt.h
> @@ -27,26 +27,51 @@ extern void (*const __init_array_end[])(int, char **, char**) __attribute__((wea
>  extern void (*const __fini_array_start[])(void) __attribute__((weak));
>  extern void (*const __fini_array_end[])(void) __attribute__((weak));
>  
> -void _start_c(long *sp);
> -__attribute__((weak,used))
> +void __start_c(long argc, char **argv, char **envp, const unsigned long *auxv);
> +__attribute__((weak, used))

We now have an additional never-inlined, global function.
This should stay inlinable in the regular case.

>  #if __nolibc_has_feature(undefined_behavior_sanitizer)
>  	__attribute__((no_sanitize("function")))
>  #endif
> -void _start_c(long *sp)
> +void __no_stack_protector __start_c(long argc, char **argv, char **envp, const unsigned long *auxv)

Please some better naming.

_start_c_global_data() or something.

>  {
> -	long argc;
> -	char **argv;
> -	char **envp;
> -	int exitcode;
>  	void (* const *ctor_func)(int, char **, char **);
>  	void (* const *dtor_func)(void);
> -	const unsigned long *auxv;
>  	/* silence potential warning: conflicting types for 'main' */
>  	int _nolibc_main(int, char **, char **) __asm__ ("main");
> +	int exitcode;
>  
>  	/* initialize stack protector */
>  	__stack_chk_init();
>  
> +	environ = envp;
> +	_auxv = auxv;
> +
> +	for (ctor_func = __preinit_array_start; ctor_func < __preinit_array_end; ctor_func++)
> +		(*ctor_func)(argc, argv, envp);
> +	for (ctor_func = __init_array_start; ctor_func < __init_array_end; ctor_func++)
> +		(*ctor_func)(argc, argv, envp);
> +
> +	/* go to application */
> +	exitcode = _nolibc_main(argc, argv, envp);
> +
> +	for (dtor_func = __fini_array_end; dtor_func > __fini_array_start;)
> +		(*--dtor_func)();
> +
> +	exit(exitcode);
> +}
> +
> +void _start_c(long *sp);
> +__attribute__((weak, used))
> +#if __nolibc_has_feature(undefined_behavior_sanitizer)
> +	__attribute__((no_sanitize("function")))
> +#endif

Now that this is repeated, it should be behind a #define.

> +void __no_stack_protector _start_c(long *sp)
> +{

(...)