linux-kernel - Re: [PATCH 1/1] x86/vdso: use the right GDT_ENTRY_CPUNODE for 32-bit getcpu() on 64-bit kernel

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Message-ID: <5e84fd48-459d-8850-d26f-860c6d34a9ad@intel.com>
Date:   Mon, 13 Mar 2023 08:22:32 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Xin Li <xin3.li@...el.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, bigeasy@...utronix.de,
        yujie.liu@...el.com, shan.kang@...el.com
Subject: Re: [PATCH 1/1] x86/vdso: use the right GDT_ENTRY_CPUNODE for 32-bit
 getcpu() on 64-bit kernel

On 3/11/23 00:48, Xin Li wrote:
>  #define GDT_ENTRY_ESPFIX_SS		26
>  #define GDT_ENTRY_PERCPU		27
> +#ifndef BUILD_VDSO32_64
>  #define GDT_ENTRY_CPUNODE		28
> +#else
> +#define GDT_ENTRY_CPUNODE		15
> +#endif

Isn't this kinda a hack?

First, it means that we'll now have two duplicate versions of this:

	#define GDT_ENTRY_CPUNODE		15

in the same file.

Second, if any other users of fake_32bit_build.h for the VDSO show up,
they'll need a similar #ifdef.

I think I'd much rather if we define all of the GDT_ENTRY_* macros in
*one* place, then make that *one* place depend on BUILD_VDSO32_64.

Also, about the *silent* failure...  Do we not have a selftest for this
somewhere?