Build for RISC-V with LLVM

[Nathaniel Hourt <i@nathaniel.land>]

Hi, all

I am trying to build u-boot and SPL for my Mars board (riscv, variant of 
the starfive visionfive2) following the board-specific docs [1], using 
LLVM/clang as my toolchain with the HOSTCC and CC make options mentioned 
in [2]. I'm building from a RISC-V native chroot using qemu-binfmt so I 
am not using the cross-compile options; thus my make invocation looks 
like `make HOSTCC=clang CC=clang` (for OpenSBI, I just pass 'LLVM=1'). 
Note that the chroot I'm building from does not contain gcc/binutils at 
all; LLVM is the only toolchain present.

The build usually succeeds, so I try to pass the SPL to the MaskROM over 
UART (using the u-boot-spl.bin.normal.out image) and it just hangs. No 
output, no response, and I have to reset the board. If I pass a working 
SPL I downloaded, it logs some output then accepts a main u-boot payload 
over UART, so if I send the main u-boot payload I built (u-boot.itb), I 
get a "Load address misaligned" error as in [3].

I attempted to configure my SPL to log to UART by turning on various 
logging options in `menuconfig`, including the options recently 
mentioned by Heinrich Schuchardt in [4], but I have been unsuccessful in 
getting any output from the SPL I built.

So I am looking for guidance. Is building with LLVM/clang (for riscv) 
supported? I don't know what to try next.

Thanks
—
Nathaniel


[1] 
https://docs.u-boot.org/en/latest/board/starfive/milk-v_mars.html#milk-v-mars
[2] https://docs.u-boot.org/en/latest/build/clang.html
[3] https://pastebin.com/xwEcqEpz
[4] https://lists.denx.de/pipermail/u-boot/2025-April/586264.html