From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp34.i.mail.ru (smtp34.i.mail.ru [94.100.177.94]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dev.tarantool.org (Postfix) with ESMTPS id 90780469710 for ; Wed, 20 May 2020 02:31:30 +0300 (MSK) From: Vladislav Shpilevoy Date: Wed, 20 May 2020 01:31:27 +0200 Message-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Subject: [Tarantool-patches] [PATCH 1/1] build: turn off LTO for exports.c List-Id: Tarantool development patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: tarantool-patches@dev.tarantool.org, tsafin@tarantool.org, avtikhon@tarantool.org There were lots of errors of kind: /builds/M4RrgQZ3/0/tarantool/tarantool/src/exports.h:395:1: error: variable ‘uuid_nil’ redeclared as function EXPORT(uuid_nil) ^ /builds/M4RrgQZ3/0/tarantool/tarantool/src/lib/uuid/tt_uuid.c:39:22: note: previously declared here const struct tt_uuid uuid_nil; when LTO was enabled. That happened because exports.c file, to take symbol addresses, declared lots of functions and variables from all the code base as extern void (void); This is crazy, but it worked for normal builds. Because symbol is symbol. The compilers couldn't find conflicting declarations, because they never met in one compilation unit. However the lie was revealed by linker with LTO enabled. It could see, that actual symbol definitions didn't match their exports in exports.c. It could live with mismatching function-function or variable-variable cases, but couldn't withstand function-variable mismatches. When a symbol was declared as a variable in one place and as a function in another. This was the case for variables: - uuid_nil - tarantool_lua_ibuf - log_pid - log_format - crc32_calc - _say - log_level The errors were false positive, because the symbols were never used for anything except taking their addresses. To calm the linker down exports.c now does not participate in LTO. Closes #5001 --- Branch: http://github.com/tarantool/tarantool/tree/gerold103/gh-5001-lto-exports-fnolto Issue: https://github.com/tarantool/tarantool/issues/5001 src/CMakeLists.txt | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt index 7a718fde9..c2fb7841c 100644 --- a/src/CMakeLists.txt +++ b/src/CMakeLists.txt @@ -246,6 +246,19 @@ if(BUILD_STATIC) endif() endif() +if (ENABLE_LTO) + # Exports compilation unit is entirely a hack. It references + # symbols among static libraries and object files declaring + # them all as functions. To avoid header dependencies. This is + # not detected by the compilers, since they never see + # conflicting definitions in one compilation unit. But this + # makes LTO mad, because the linker sees all the definitions, + # and is especially angry when a variable is declared as a + # function. To get rid of these false positive errors the + # exports file is not link-time optimized. + set_source_files_properties(exports.c PROPERTIES COMPILE_FLAGS -fno-lto) +endif() + add_executable( tarantool main.cc exports.c ${LIBUTIL_FREEBSD_SRC}/flopen.c -- 2.21.1 (Apple Git-122.3)