linux-kernel - Re: [RFC PATCH V3 00/43] rv64ilp32_abi: Build CONFIG

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Message-ID: <20250327210625.7a3021d0@pumpkin>
Date: Thu, 27 Mar 2025 21:06:25 +0000
From: David Laight <david.laight.linux@...il.com>
To: guoren@...nel.org
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Subject: Re: [RFC PATCH V3 00/43] rv64ilp32_abi: Build CONFIG_64BIT
 kernel-self with ILP32 ABI

On Tue, 25 Mar 2025 08:15:41 -0400
guoren@...nel.org wrote:

> From: "Guo Ren (Alibaba DAMO Academy)" <guoren@...nel.org>
> 
> Since 2001, the CONFIG_64BIT kernel has been built with the LP64 ABI,
> but this patchset allows the CONFIG_64BIT kernel to use an ILP32 ABI
> for construction to reduce cache & memory footprint (Compared to
> kernel-lp64-abi, kernel-rv64ilp32-abi decreased the used memory by
> about 20%, as shown in "free -h" in the following demo.)
...

Why on earth would you want to run a 64bit application on a 32bit kernel.
IIRC the main justification for 64bit was to get a larger address space.

Now you might want to compile a 32bit (ILP32) system that actually
runs in 64bit mode (c/f x32) so that 64bit maths (long long) is
more efficient - but that is a different issue.
(I suspect you'd need to change the process switch code to save
all 64bits of the registers - but maybe not much else??)

	David