Re: [PATCH] riscv: Fix build against binutils 2.38

Aurelien Jarno
2022-01-28T18:28:38Z

On 2022-01-28 19:19, Aurelien Jarno wrote:
> On 2022-01-28 19:03, Heinrich Schuchardt wrote:
> > On 1/28/22 14:47, Alexandre Ghiti wrote:
> > > The following description is copied from the equivalent patch for the
> > > Linux Kernel proposed by Aurelien Jarno:
> > >
> > > From version 2.38, binutils default to ISA spec version 20191213. This
> > > means that the csr read/write (csrr*/csrw*) instructions and fence.i
> > > instruction has separated from the `I` extension, become two standalone
> > > extensions: Zicsr and Zifencei. As the kernel uses those instruction,
> > > this causes the following build failure:
> > >
> > > arch/riscv/cpu/mtrap.S: Assembler messages:
> > > arch/riscv/cpu/mtrap.S:65: Error: unrecognized opcode `csrr a0,scause'
> > > arch/riscv/cpu/mtrap.S:66: Error: unrecognized opcode `csrr a1,sepc'
> > > arch/riscv/cpu/mtrap.S:67: Error: unrecognized opcode `csrr a2,stval'
> > > arch/riscv/cpu/mtrap.S:70: Error: unrecognized opcode `csrw sepc,a0'
> >
> > I tried to build qemu-riscv64_smode_defconfig. With your patch I get
> >
> > arch/riscv/cpu/cpu.c: Assembler messages:
> > arch/riscv/cpu/cpu.c:94: Error: unrecognized opcode `csrs sstatus,a5'
> > arch/riscv/cpu/cpu.c:95: Error: unrecognized opcode `csrw 0x003,0'
> >
> > The build flag used is -march=rv64imac.
> >
> > My toolchain is:
> > binutils 2.37.90.20220126-0ubuntu1
> > riscv64-linux-gnu-gcc (Ubuntu 10.3.0-8ubuntu1) 10.3.0
> >
> > This GCC does not support _zicsr_zifencei:
> > cc1: error: ‘-march=rv64imac_zicsr_zifencei’: unsupported ISA subset ‘z
> >
> > Could it be that the GCC is too old for the new binutils?
> > When was the z subset added to GCC?
>
> Yes, GCC 11 is the minimum version that understand those extensions.

GCC 11 is also required to support the not recommended alternative fix
-misa-spec=2.2.

If you need to support GCC 10, it seems that the only option is to build
binutils with --with-isa-spec=2.2.

--
Aurelien Jarno GPG: 4096R/1DDD8C9B
aurelien@aurel32.net http://www.aurel32.net