Date:   Mon, 27 Feb 2023 15:18:43 +0000 (GMT)
From:   "Maciej W. Rozycki" <macro@orcam.me.uk>
To:     Johan Almbladh <johan.almbladh@anyfinetworks.com>
cc:     Jiaxun Yang <jiaxun.yang@flygoat.com>,
        "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
        linux-kernel@vger.kernel.org,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        "paulburton@kernel.org" <paulburton@kernel.org>,
        bpf@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: [PATCH 2/2] MIPS: ebpf jit: Implement R4000 workarounds
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References: <20230222161222.11879-1-jiaxun.yang@flygoat.com> <20230222161222.11879-3-jiaxun.yang@flygoat.com> <CAM1=_QTDkYJANgxYwkgPZB+hUX6Rr_Pvnn7cFwSJFHQtLrpQMA@mail.gmail.com> <70C80F6D-A727-48FD-A767-A2CA54AA7C1E@flygoat.com>
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On Mon, 27 Feb 2023, Johan Almbladh wrote:

> > > R4000 is a 64-bit CPU, so the 32-bit JIT implementation will not be
> > > used. From the Makefile:
> > >
> > > ifeq ($(CONFIG_32BIT),y)
> > >        obj-$(CONFIG_BPF_JIT) += bpf_jit_comp32.o
> > > else
> > >        obj-$(CONFIG_BPF_JIT) += bpf_jit_comp64.o
> > > endif
> >
> > It’s common practice to run 32-bit kernel on R4000 based systems to save some memory :-)
> 
> Ok, I understand.

 Likewise:

	select CPU_R4000_WORKAROUNDS if 64BIT
	select CPU_R4400_WORKAROUNDS if 64BIT

This only applies to 64-bit operations, which are not used in 32-bit code 
(one reason why these early silicon revisions were originally used with 
32-bit software only).

  Maciej