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[81.147.8.54]) by smtp.gmail.com with ESMTPSA id k39-20020a05600c1ca700b003a84375d0d1sm37610260wms.44.2022.12.30.09.12.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 Dec 2022 09:12:31 -0800 (PST) Received: by nz.home (Postfix, from userid 1000) id E10B38EA33883; Fri, 30 Dec 2022 17:12:30 +0000 (GMT) Date: Fri, 30 Dec 2022 17:12:30 +0000 From: Sergei Trofimovich To: bug-gnulib@gnu.org Cc: libc-alpha@sourceware.org Subject: gnulib's obstack_* symbols in dynamic exports on glibc. Intentional? Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,RCVD_IN_BARRACUDACENTRAL,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Hello bug-gnulib (and libc-alpha, CCed)! The other day I was looking at simplest programs to make sure they don't normally have dynamic exports. I picked coreutils-9.1 'ls'. And to my surprise it did have one a set of dynamically exported symbols: $ nm -D `which ls` | grep -v '^ ' 00000000004c0d40 T _obstack_allocated_p 0000000000534808 D obstack_alloc_failed_handler 00000000004c0bd0 T _obstack_begin 00000000004c0bf0 T _obstack_begin_1 00000000004c0d80 T _obstack_free 00000000004c0e00 T _obstack_memory_used 00000000004c0c10 T _obstack_newchunk That was a surprise to me. I think they are exported because gnulib defines them in obstack.c. AFAIU gnulib assumes that local implementation is better that glibc's as it supports 64-bit object sizes. I think ld decides to put symbols into dynamic exports to make sure local symbols intended to override glibc's need to propagate to glibc and other libraries that might use it. Questions: 1. Is it a safe override to mangle symbols ilke that? Or would glibc's versioned symbols be used just fine by existing libraries? $ nm -D /lib/libc.so.6 | fgrep obstack 0000000000201338 B _obstack@GLIBC_2.2.5 000000000009aa70 T _obstack_allocated_p@@GLIBC_2.2.5 00000000001fb338 D obstack_alloc_failed_handler@@GLIBC_2.2.5 000000000009a780 T _obstack_begin@@GLIBC_2.2.5 000000000009a840 T _obstack_begin_1@@GLIBC_2.2.5 00000000001fa208 D obstack_exit_failure@@GLIBC_2.2.5 000000000009aab0 T _obstack_free@@GLIBC_2.2.5 000000000009aab0 T obstack_free@@GLIBC_2.2.5 000000000009ab40 T _obstack_memory_used@@GLIBC_2.2.5 000000000009a900 T _obstack_newchunk@@GLIBC_2.2.5 000000000007e110 W obstack_printf@@GLIBC_2.2.5 000000000011e9c0 T __obstack_printf_chk@@GLIBC_2.8 000000000007e100 W obstack_vprintf@@GLIBC_2.2.5 000000000011ea80 T __obstack_vprintf_chk@@GLIBC_2.8 2. Would it be feasible to avoid dynamic symbol export and maybe rename gnulib's symbols to avoid clash with glibc? I would expect loading to be a tiny bit faster for binaries without dynamic exports like that. Thanks! -- Sergei