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[176.36.0.241]) by smtp.gmail.com with ESMTPSA id lf8-20020a170906ae4800b00a3c6528ec4csm1737908ejb.135.2024.02.13.15.36.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Feb 2024 15:36:59 -0800 (PST) Message-ID: <7af0d2e0cc168eb8f57be0fe185d7fa9caf87824.camel@gmail.com> Subject: Re: [PATCH v2 bpf-next 14/20] libbpf: Recognize __arena global varaibles. From: Eduard Zingerman To: Andrii Nakryiko Cc: Alexei Starovoitov , bpf@vger.kernel.org, daniel@iogearbox.net, andrii@kernel.org, memxor@gmail.com, tj@kernel.org, brho@google.com, hannes@cmpxchg.org, lstoakes@gmail.com, akpm@linux-foundation.org, urezki@gmail.com, hch@infradead.org, linux-mm@kvack.org, kernel-team@fb.com Date: Wed, 14 Feb 2024 01:36:58 +0200 In-Reply-To: References: <20240209040608.98927-1-alexei.starovoitov@gmail.com> <20240209040608.98927-15-alexei.starovoitov@gmail.com> Autocrypt: addr=eddyz87@gmail.com; prefer-encrypt=mutual; keydata=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 A+T7mluw nYzhLWGcczc6J71q1Dje0l5vIPaSFOgwmWD4DA+WvuxM/shH4rtWeodbv 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 IYKvsh7s t1iq+gsfnXbPz5AnS598ScZI1oP7OrPSFJkt/z4acEbOQDQs8aUqrd46PV jsdqGvKnXZxzylux29UTNby4jTlz9pNJM+wPrDRmGfchLDUmf6CffaUYCbu4FiId+9+dcTCDvxbABRy1C3OJ8QY7cxfJ+pEZW18fRJ0XCl/fiV/ecAOfB3HsqgTzAn555h0rkFgay0hAvMU/mAW/CFNSIxV397zm749ZNLA0L2dMy1AKuOqH+/B+/ImBfJMDjmdyJQ8WU/OFRuGLdqOd2oZrA1iuPIa+yUYyZkaZfz/emQwpIL1+Q4p1R/OplA4yc301AqruXXUcVDbEB+joHW3hy5FwK5t5OwTKatrSJBkydSF9zdXy98fYzGniRyRA65P0Ix/8J3BYB4edY2/w0Ip/mdYsYQljBY0A== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 28AAA20003 X-Stat-Signature: 5mjefoxbtik45bumz1q6ucaxjmpwkcjk X-HE-Tag: 1707867421-570208 X-HE-Meta: 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 Huhu5KMW qGOJponYz/iJXetehfPozaYoKiCEN9itnmCEw5lcGhla1tpgWkRAZ7xma0WgSFmFOAgRU2Gf8d+NXhOJANAIoLEbOvsrOEFBpUK3BxT02pLu38QDTWfEvRrbFkqtX+hjnamo4O/dc/VL6IqCoCgqQucFPIXiZHyKBtJ+lCzHrCG9fdzvT5gKb2gNpkwHvbeArXcHpvcXPPVJYUlQ2z//e60lOm+d0ayelJUnewRmol7jwOtBSy18XeN+LTsc7ag+Txc7bl9lQ3/4/W21t2pQ0/fT0/w2+N/7KWhK9qHjXjKmw9GjRKQjkY9LGCxN2dgrHjF6Wh0A/635qkTUjtZ6a0vKLDVIF1rAepqHFYijIe4qhfPLZLlNNTFTu2rys6+Rmhe1O9IxaeAy/8j0nySxV3ICHD0od28aC6Z3QHI0YYRgX8un/IYveDB7o02XacRWvT3OY6korn4LMnKc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.009710, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 2024-02-13 at 15:17 -0800, Andrii Nakryiko wrote: [...] > > So, at first I thought that having two maps is a bit of a hack. >=20 > yep, that was my instinct as well >=20 > > However, after trying to make it work with only one map I don't really > > like that either :) >=20 > Can you elaborate? see my reply to Alexei, I wonder how did you think > about doing this? Relocations in the ELF file are against a new section: ".arena.1". This works nicely with logic in bpf_program__record_reloc(). If single map is used, we effectively need to track two indexes for the map section: - one used for relocations against map variables themselves (named "generic map reference relocation" in the function code); - one used for relocations against ".arena.1" (named "global data map relocation" in the function code). This spooked me off: - either bpf_object__init_internal_map() would have a specialized branch for arenas, as with current approach; - or bpf_program__record_reloc() would have a specialized branch for arenas= , as with one map approach. Additionally, skel generation logic currently assumes that mmapable bindings would be generated only for internal maps, but that is probably not a big deal.