# git rev-parse -q --verify 7e67dd4899d866115be2f68fa3f328616cd60408^{commit}
# git fetch -q -n -f git://gitlab.ozlabs.ibm.com/mirror/linux-kbuild.git for-next
remote: warning: multi-pack bitmap is missing required reverse index        
# git rev-parse -q --verify 7e67dd4899d866115be2f68fa3f328616cd60408^{commit}
7e67dd4899d866115be2f68fa3f328616cd60408
# git checkout -q -f -B kisskb 7e67dd4899d866115be2f68fa3f328616cd60408
# git clean -qxdf
# < git log -1
# commit 7e67dd4899d866115be2f68fa3f328616cd60408
# Author: Masahiro Yamada <masahiroy@kernel.org>
# Date:   Sat Jun 10 18:13:10 2023 +0900
# 
#     Revert "[PATCH] uml: export symbols added by GCC hardened"
#     
#     This reverts commit cead61a6717a9873426b08d73a34a325e3546f5d.
#     
#     It exported __stack_smash_handler and __guard, while they may not be
#     defined by anyone.
#     
#     The code *declares* __stack_smash_handler and __guard. It does not
#     create weak symbols. If no external library is linked, they are left
#     undefined, but yet exported.
#     
#     If a loadable module tries to access non-existing symbols, bad things
#     (a page fault, NULL pointer dereference, etc.) will happen. So, the
#     current code is wrong and dangerous.
#     
#     If the code were written as follows, it would *define* them as weak
#     symbols so modules would be able to get access to them.
#     
#       void (*__stack_smash_handler)(void *) __attribute__((weak));
#       EXPORT_SYMBOL(__stack_smash_handler);
#     
#       long __guard __attribute__((weak));
#       EXPORT_SYMBOL(__guard);
#     
#     In fact, modpost forbids exporting undefined symbols. It shows an error
#     message if it detects such a mistake.
#     
#       ERROR: modpost: "..." [...] was exported without definition
#     
#     Unfortunately, it is checked only when the code is built as modular.
#     The problem described above has been unnoticed for a long time because
#     arch/um/os-Linux/user_syms.c is always built-in.
#     
#     With a planned change in Kbuild, exporting undefined symbols will always
#     result in a build error instead of a run-time error. It is a good thing,
#     but we need to fix the breakage in advance.
#     
#     One fix is to define weak symbols as shown above. An alternative is to
#     export them conditionally as follows:
#     
#       #ifdef CONFIG_STACKPROTECTOR
#       extern void __stack_smash_handler(void *);
#       EXPORT_SYMBOL(__stack_smash_handler);
#     
#       external long __guard;
#       EXPORT_SYMBOL(__guard);
#       #endif
#     
#     This is what other architectures do; EXPORT_SYMBOL(__stack_chk_guard)
#     is guarded by #ifdef CONFIG_STACKPROTECTOR.
#     
#     However, adding the #ifdef guard is not sensible because UML cannot
#     enable the stack-protector in the first place! (Please note UML does
#     not select HAVE_STACKPROTECTOR in Kconfig.)
#     
#     So, the code is already broken (and unused) in multiple ways.
#     
#     Just remove.
#     
#     Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
#     Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
# < /opt/cross/kisskb/korg/gcc-11.3.0-nolibc/aarch64-linux/bin/aarch64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-11.3.0-nolibc/aarch64-linux/bin/aarch64-linux-ld --version
# < git log --format=%s --max-count=1 7e67dd4899d866115be2f68fa3f328616cd60408
# make -s -j 160 ARCH=arm64 O=/kisskb/build/kbuild_defconfig_arm64-gcc11 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-11.3.0-nolibc/aarch64-linux/bin/aarch64-linux-  defconfig
# < make -s -j 160 ARCH=arm64 O=/kisskb/build/kbuild_defconfig_arm64-gcc11 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-11.3.0-nolibc/aarch64-linux/bin/aarch64-linux-  help
# make -s -j 160 ARCH=arm64 O=/kisskb/build/kbuild_defconfig_arm64-gcc11 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-11.3.0-nolibc/aarch64-linux/bin/aarch64-linux-  olddefconfig
# make -s -j 160 ARCH=arm64 O=/kisskb/build/kbuild_defconfig_arm64-gcc11 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-11.3.0-nolibc/aarch64-linux/bin/aarch64-linux-  
Completed OK
# rm -rf /kisskb/build/kbuild_defconfig_arm64-gcc11
# Build took: 0:07:03.257978