From 19b7f854a274812d9c95fc7aaf134a12530c105f Mon Sep 17 00:00:00 2001 From: Thiago Macieira Date: Mon, 23 Jan 2012 11:46:58 -0200 Subject: Enable -mno-direct-extern-access and ELF protected visibility The -mno-direct-extern-access tells the compiler and linker that references to symbols outside this ELF module mustn't be direct and must instead always go through the GOT or PLT (the PLT can additionally be disabled with -fno-plt). The ELF protected visibility tells the compiler and linker that this symbol is present in the dynamic symbol table as an export, but it cannot be interposed by another ELF module. This option is required for user code to link properly to Qt, otherwise they will get linker errors (assuming GNU binutils >= 2.39) or runtime failures (glibc >= 2.35). Both versions of glibc and binutils are older than GCC 12, so it's a safe assumption they are in use and downgrading the toolchain or libc is not supported. Adding this option to the compilation is assured for CMake and qmake-based projects. For example, all accessess to QCoreApplication::self in QtCore, after this change and with GCC 12 are relocation-free and direct: 000000000013ebf0 : 13ebf0: cmpq $0x0,0x4f73d0(%rip) # 635fc8 13ebf8: setne %al 13ebfb: je a90fe 13ec01: ret Meanwhile, accesses to the same variable in other modules are indirect via the GOT: 66650: mov 0x876e1(%rip),%rax # edd38 66657: cmpq $0x0,(%rax) This replaces the -Bsymbolic and -Bsymbolic-functions (broken) functionality that Qt has been using or attempting to use since ~2006. See https://gitlab.com/x86-psABIs/x86-64-ABI/-/issues/8#note_606975128 Change-Id: Iad4b0a3e5c06570b9f5f571b26ed564aa0811e47 Reviewed-by: Alexandru Croitor Reviewed-by: Lars Knoll --- cmake/QtPlatformTargetHelpers.cmake | 3 +++ 1 file changed, 3 insertions(+) (limited to 'cmake/QtPlatformTargetHelpers.cmake') diff --git a/cmake/QtPlatformTargetHelpers.cmake b/cmake/QtPlatformTargetHelpers.cmake index 36b661741b..270ed3167b 100644 --- a/cmake/QtPlatformTargetHelpers.cmake +++ b/cmake/QtPlatformTargetHelpers.cmake @@ -30,6 +30,9 @@ function(qt_internal_setup_public_platform_target) target_compile_options(Platform INTERFACE "-stdlib=libc++") target_link_options(Platform INTERFACE "-stdlib=libc++") endif() + if (QT_FEATURE_no_extern_direct_access) + target_compile_options(Platform INTERFACE "-mno-direct-extern-access") + endif() qt_set_msvc_cplusplus_options(Platform INTERFACE) -- cgit v1.2.3