From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 1944) id 65A4E3842434; Thu, 14 Jan 2021 11:12:07 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 65A4E3842434 Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit From: Szabolcs Nagy To: glibc-cvs@sourceware.org Subject: [glibc/nsz/bug27072] Make libc symbols hidden in static PIE X-Act-Checkin: glibc X-Git-Author: Szabolcs Nagy X-Git-Refname: refs/heads/nsz/bug27072 X-Git-Oldrev: 48b4bbc75a8ca1c653a507f120a4e98641088060 X-Git-Newrev: dfffe46e62b310e9cadd86e99d85121951e8f881 Message-Id: <20210114111207.65A4E3842434@sourceware.org> Date: Thu, 14 Jan 2021 11:12:07 +0000 (GMT) X-BeenThere: glibc-cvs@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Glibc-cvs mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 14 Jan 2021 11:12:07 -0000 https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=dfffe46e62b310e9cadd86e99d85121951e8f881 commit dfffe46e62b310e9cadd86e99d85121951e8f881 Author: Szabolcs Nagy Date: Wed Jan 6 11:31:04 2021 +0000 Make libc symbols hidden in static PIE Hidden matters with static PIE: extern symbol access in position independent code usually involves GOT indirections which needs RELATIVE relocs in a static linked PIE. Hidden visibility avoids indirections and RELATIVE relocs on targets that can access symbols pc-relative. The check should use IS_IN_LIB instead of IS_IN(libc) since all static libraries can use hidden visibility to avoid indirections, however the test system links objects from libcrypt.a into dynamic linked test binaries so hidden does not work there. I think mixing static and shared libc components in the same binary should not be supported usage, but to be safe only use hidden in libc.a. There are targets (i686) where hidden visibility functions are problematic in PIE code so hidden cannot be applied to all symbols. Then static PIE requires extern object access without relocations (e.g. by relying on copy relocations in shared libraries instead of GOT access in PIE code). See bug 14961. From -static-pie linked 'int main(){}' this shaves off 73 relative relocs on aarch64 and reduces code size too. Diff: --- include/libc-symbols.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/include/libc-symbols.h b/include/libc-symbols.h index ea126ae70c..f4dd735555 100644 --- a/include/libc-symbols.h +++ b/include/libc-symbols.h @@ -434,13 +434,18 @@ for linking") strong_alias(real, name) #endif -#if defined SHARED || defined LIBC_NONSHARED \ - || (BUILD_PIE_DEFAULT && IS_IN (libc)) +#if defined SHARED || defined LIBC_NONSHARED # define attribute_hidden __attribute__ ((visibility ("hidden"))) #else # define attribute_hidden #endif +/* Mark all symbols hidden in static PIE libc to avoid GOT indirections. */ +#if BUILD_PIE_DEFAULT && !defined NO_HIDDEN_EXTERN_FUNC_IN_PIE \ + && IS_IN (libc) && !defined LIBC_NONSHARED +# pragma GCC visibility push(hidden) +#endif + #define attribute_tls_model_ie __attribute__ ((tls_model ("initial-exec"))) #define attribute_relro __attribute__ ((section (".data.rel.ro")))