[gentoo-dev] How to structure our RISC-V support

["Andreas K. Huettel" <dilfridge@gentoo.org>]

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Howdy. 

I'm sending this not only to the team members on the alias, but also 
to the whole dev list for discussion. 

So far I've been trying to support in Gentoo the full risc-v multilib 
directory structure and the ABI sets supported by glibc. According to 
specs this means for riscv64 

-mabi=rv64gc -march=lp64d 
  libdir = lib64/lp64d
  ("hardfloat")

-mabi=rv64imac -march=lp64
  libdir = lib64/lp64
  ("softfloat")

and theoretically similar for riscv32 (which just landed in glibc and 
is still broken in qemu-user).

However, this leads to several levels of pain (and I definitely dont 
have time to deal with it myself):

a) In many places the two-level libdir (e.g., /usr/lib64/lp64d) leads 
to difficulties in build systems. Right now Qt5 and CMake are still 
somewhat broken (in *Gentoo*).

b) Rust only supports rv64gc/lp64d. (Which is arguably what you should 
have for decent Linux support.)

I'm pretty sure these are not the only things, but they are somewhat 
symptomatic.

So, I would like to bring two proposals up for discussion.

1) We stop caring about anything except rv64gc/lp64d.
People can still bootstrap other stuff with crossdev etc, but the 
Gentoo tree and the riscv keyword reflect that things work with above 
-mabi and -march settings.

2) We drop the multilib paths and use "normal" lib64, with additional 
"safety symlinks" (/usr)/lib64/lp64d -> .
This is what SuSE and (I think) Fedora already does. The symlink 
should be there since "lib64" is NOT an official fallback coded into 
gcc/glibc/binutils; the only fallback present is "lib" ...

Opinions?

Cheers,
Andreas



-- 
Andreas K. Hüttel
dilfridge@gentoo.org
Gentoo Linux developer
(council, toolchain, base-system, perl, libreoffice)

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