Re: [PATCH 17/17] riscv: add nommu support

[Vladimir Murzin]

On 6/10/19 11:16 PM, Christoph Hellwig wrote:
> Most of the patch is just stubbing out code not needed without page
> tables, but there is an interesting detail in the signals implementation:
> 
>  - The normal RISC-V syscall ABI only implements rt_sigreturn as VDSO
>    entry point, but the ELF VDSO is not supported for nommu Linux.
>    We instead copy the code to call the syscall onto the stack.

On ARM we perform I/D cache synchronization after stack manipulation.

OTOH, ARM port of uClibc provides SA_RESTORER with intention to avoid
manipulation with stack and cache maintenance operations (yet kernel
still performs such manipulation, IIUC, for backward compatibility)

Cheers
Vladimir