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Re: Semihosting, arm, riscv, ppc and common code

From: Liviu Ionescu
Subject: Re: Semihosting, arm, riscv, ppc and common code
Date: Wed, 15 Jan 2020 14:30:17 +0200

> On 15 Jan 2020, at 14:01, Alex Bennée <address@hidden> wrote:
> ... AFAIK the main users of arm linux user
> are compiler test cases for M-profile CPUs. 

I confirm, generally unit tests.

But not necessarily, I used QEMU as the main development platform for the 
Cortex-M port of µOS++, a C/C++ framework/RTOS, and it was very convenient.

> ... Is semihosting even
> going to be a thing on real RiscV/Power silicon?

Even for Arm it is a thing of debuggers and development environments, not of 
silicon itself, since it requires no special hardware support, a BRK 
instruction is enough.

From a software point of view it would be beneficial to use the same 
semihosting protocol on other non-Arm architectures too, even if it is far from 

I pushed hard for adopting the Arm semihosting for RISC-V, and even contributed 
the semihosting code for OpenOCD RISC-V, but officially the only mention of 
semihosting in the RISC-V specs is in the notes sections, where it is mentioned 
how to use the BRK instruction to invoke semihosting calls (RISC-V has a single 
BREAK instructions, and to make it unique it must be surrounded by some hint 



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