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From: Eduard Zingerman To: Alexei Starovoitov , bpf@vger.kernel.org Cc: 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: Tue, 13 Feb 2024 02:34:45 +0200 In-Reply-To: <20240209040608.98927-15-alexei.starovoitov@gmail.com> 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-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 730501C0014 X-Stat-Signature: 9f9sdy69imcocwiu6cqfqbkkub899cw6 X-Rspam-User: X-HE-Tag: 1707784489-16594 X-HE-Meta: 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 15E+ahje 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.004919, 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 Thu, 2024-02-08 at 20:06 -0800, Alexei Starovoitov wrote: > From: Alexei Starovoitov >=20 > LLVM automatically places __arena variables into ".arena.1" ELF section. > When libbpf sees such section it creates internal 'struct bpf_map' LIBBPF= _MAP_ARENA > that is connected to actual BPF_MAP_TYPE_ARENA 'struct bpf_map'. > They share the same kernel's side bpf map and single map_fd. > Both are emitted into skeleton. Real arena with the name given by bpf pro= gram > in SEC(".maps") and another with "__arena_internal" name. > All global variables from ".arena.1" section are accessible from user spa= ce > via skel->arena->name_of_var. [...] I hit a strange bug when playing with patch. Consider a simple example [0]. When the following BPF global variable: int __arena * __arena bar; - is commented -- the test passes; - is uncommented -- in the test fails because global variable 'shared' is N= ULL. Note: the second __arena is necessary to put 'bar' to .arena.1 section. [0] https://github.com/kernel-patches/bpf/commit/6d95c8557c25d01ef3f13e6aef= 2bda9ac2516484