Re: [RFC PATCH V3 00/43] rv64ilp32_abi: Build CONFIG_64BIT kernel-self with ILP32 ABI

David Laight
2025-03-27T21:06:33Z

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

> From: "Guo Ren (Alibaba DAMO Academy)" <guoren@kernel.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