On Tue, 25 Mar 2025 at 05:17, <guoren@xxxxxxxxxx> wrote:
>
> The rv64ilp32 abi kernel accommodates the lp64 abi userspace and
> leverages the lp64 abi Linux interface. Hence, unify the
> BITS_PER_LONG = 32 memory layout to match BITS_PER_LONG = 64.
No.
This isn't happening.
You can't do crazy things in the RISC-V code and then expect the rest
of the kernel to just go "ok, we'll do crazy things".
We're not doing crazy __riscv_xlen hackery with random structures
containing 64-bit values that the kernel then only looks at the low 32
bits. That's wrong on *so* many levels.
I'm willing to say "big-endian is dead", but I'm not willing to accept
this kind of crazy hackery.
Not today, not ever.
If you want to run a ilp32 kernel on 64-bit hardware (and support
64-bit ABI just in a 32-bit virtual memory size), I would suggest you
(a) treat the kernel as natively 32-bit (obviously you can then tell
the compiler to use the rv64 instructions, which I presume you're
already doing - I didn't look)
(b) look at making the compat stuff do the conversion the "wrong way".
And btw, that (b) implies *not* just ignoring the high bits. If
user-space gives 64-bit pointer, you don't just treat it as a 32-bit
one by dropping the high bits. You add some logic to convert it to an
invalid pointer so that user space gets -EFAULT.
Linus
