linux-kernel - Re: [PATCH 4/5] x86/uapi: Stop leaking kconfig references to userspace

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Message-Id: <a745a59f-947c-4847-b31c-5e32125a51a4@app.fastmail.com>
Date: Tue, 30 Dec 2025 22:08:04 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
 "Vineet Gupta" <vgupta@...nel.org>, "Russell King" <linux@...linux.org.uk>,
 "Dinh Nguyen" <dinguyen@...nel.org>, "Thomas Gleixner" <tglx@...utronix.de>,
 "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
 "Dave Hansen" <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>
Cc: linux-snps-arc@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 4/5] x86/uapi: Stop leaking kconfig references to userspace

On Tue, Dec 30, 2025, at 08:10, Thomas Weißschuh wrote:
> 
>  /* entries in ARCH_DLINFO: */
> -#if defined(CONFIG_IA32_EMULATION) || !defined(CONFIG_X86_64)
> +#if defined(__KERNEL__) && (defined(CONFIG_IA32_EMULATION) || 
> !defined(CONFIG_X86_64))
>  # define AT_VECTOR_SIZE_ARCH 3
>  #else /* else it's non-compat x86-64 */
>  # define AT_VECTOR_SIZE_ARCH 2

While this patch clearly keeps the current behavior, I think it's
wrong, and 32-bit userspace should see a '3' instead of '2' here.

It can probably just be '3' unconditionally, or we can
make it more complex and have a userspace definition based
on __x86_64__ being defined.

I also wonder if there is a problem with the third
x86-64 entry being zero rather than AT_IGNORE. I see that
some architectures do it like this, to keep the number constant
even if some entries are missing:

        if (likely(signal_minsigstksz))                          \
                NEW_AUX_ENT(AT_MINSIGSTKSZ, signal_minsigstksz); \
        else                                                     \
                NEW_AUX_ENT(AT_IGNORE, 0);                       \

     Arnd