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[104.199.75.203]) by smtp.gmail.com with ESMTPSA id v64sm2420265wme.25.2020.12.04.01.12.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Dec 2020 01:12:25 -0800 (PST) Date: Fri, 4 Dec 2020 09:12:21 +0000 From: Brendan Jackman To: Yonghong Song Cc: bpf@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , KP Singh , Florent Revest , linux-kernel@vger.kernel.org, Jann Horn Subject: Re: [PATCH bpf-next v3 07/14] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction Message-ID: References: <20201203160245.1014867-1-jackmanb@google.com> <20201203160245.1014867-8-jackmanb@google.com> <45b3d69d-7356-2c28-e507-897889be564c@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <45b3d69d-7356-2c28-e507-897889be564c@fb.com> Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Thu, Dec 03, 2020 at 09:27:04PM -0800, Yonghong Song wrote: > On 12/3/20 8:02 AM, Brendan Jackman wrote: [...] > > diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c > > index 37c8d6e9b4cc..3ee2246a52ef 100644 > > --- a/kernel/bpf/disasm.c > > +++ b/kernel/bpf/disasm.c > > @@ -160,6 +160,13 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs, > > 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_ADD | BPF_FETCH)) { > > + verbose(cbs->private_data, "(%02x) r%d = atomic%s_fetch_add(*(%s *)(r%d %+d), r%d)\n", > > We should not do dereference here (withough first *), right? since the input > is actually an address. something like below? > r2 = atomic[64]_fetch_add((u64/u32 *)(r3 +40), r2) Ah yep - thanks! [...] > > diff --git a/tools/include/linux/filter.h b/tools/include/linux/filter.h > > index 95ff51d97f25..ac7701678e1a 100644 > > --- a/tools/include/linux/filter.h > > +++ b/tools/include/linux/filter.h > > @@ -180,6 +180,16 @@ > > .imm = BPF_ADD }) > > #define BPF_STX_XADD BPF_ATOMIC_ADD /* alias */ > > +/* Atomic memory add with fetch, src_reg = atomic_fetch_add(*(dst_reg + off), src_reg); */ > > Maybe src_reg = atomic_fetch_add(dst_reg + off, src_reg)? Yep - and the same for the bitwise ops in the later patch.