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[104.199.75.203]) by smtp.gmail.com with ESMTPSA id f4sm2552189wmb.47.2020.12.01.04.32.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Dec 2020 04:32:03 -0800 (PST) Date: Tue, 1 Dec 2020 12:32:00 +0000 From: Brendan Jackman To: Alexei Starovoitov Cc: bpf@vger.kernel.org, Alexei Starovoitov , Yonghong Song , Daniel Borkmann , KP Singh , Florent Revest , linux-kernel@vger.kernel.org, Jann Horn Subject: Re: [PATCH v2 bpf-next 08/13] bpf: Add instructions for atomic_[cmp]xchg Message-ID: <20201201123200.GF2114905@google.com> References: <20201127175738.1085417-1-jackmanb@google.com> <20201127175738.1085417-9-jackmanb@google.com> <20201129012748.i5rws2hvmqptfmy7@ast-mbp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201129012748.i5rws2hvmqptfmy7@ast-mbp> Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Sat, Nov 28, 2020 at 05:27:48PM -0800, Alexei Starovoitov wrote: > On Fri, Nov 27, 2020 at 05:57:33PM +0000, Brendan Jackman wrote: > > > > /* atomic op type fields (stored in immediate) */ > > -#define BPF_FETCH 0x01 /* fetch previous value into src reg */ > > +#define BPF_XCHG (0xe0 | BPF_FETCH) /* atomic exchange */ > > +#define BPF_CMPXCHG (0xf0 | BPF_FETCH) /* atomic compare-and-write */ > > +#define BPF_FETCH 0x01 /* fetch previous value into src reg or r0*/ > > I think such comment is more confusing than helpful. > I'd just say that the fetch bit is not valid on its own. > It's used to build other instructions like cmpxchg and atomic_fetch_add. OK sounds good. > > + } else if (BPF_MODE(insn->code) == BPF_ATOMIC && > > + insn->imm == (BPF_CMPXCHG)) { > > redundant (). Ack, thanks > > + verbose(cbs->private_data, "(%02x) r0 = atomic%s_cmpxchg(*(%s *)(r%d %+d), r0, r%d)\n", > > + insn->code, > > + BPF_SIZE(insn->code) == BPF_DW ? "64" : "", > > + bpf_ldst_string[BPF_SIZE(insn->code) >> 3], > > + insn->dst_reg, insn->off, > > + insn->src_reg); > > + } else if (BPF_MODE(insn->code) == BPF_ATOMIC && > > + insn->imm == (BPF_XCHG)) { > > redundant (). Ack, thanks