On 2021-01-29, Nick Desaulniers wrote:
On Fri, Jan 29, 2021 at 12:11 PM Nathan Chancellor <[email protected]> wrote:clang produces .eh_frame sections when CONFIG_GCOV_KERNEL is enabled, even when -fno-asynchronous-unwind-tables is in KBUILD_CFLAGS: $ make CC=clang vmlinux ... ld: warning: orphan section `.eh_frame' from `init/main.o' being placed in section `.eh_frame' ld: warning: orphan section `.eh_frame' from `init/version.o' being placed in section `.eh_frame' ld: warning: orphan section `.eh_frame' from `init/do_mounts.o' being placed in section `.eh_frame' ld: warning: orphan section `.eh_frame' from `init/do_mounts_initrd.o' being placed in section `.eh_frame' ld: warning: orphan section `.eh_frame' from `init/initramfs.o' being placed in section `.eh_frame' ld: warning: orphan section `.eh_frame' from `init/calibrate.o' being placed in section `.eh_frame' ld: warning: orphan section `.eh_frame' from `init/init_task.o' being placed in section `.eh_frame' ... $ rg "GCOV_KERNEL|GCOV_PROFILE_ALL" .config CONFIG_GCOV_KERNEL=y CONFIG_ARCH_HAS_GCOV_PROFILE_ALL=y CONFIG_GCOV_PROFILE_ALL=y This was already handled for a couple of other options in commit d812db78288d ("vmlinux.lds.h: Avoid KASAN and KCSAN's unwanted sections") and there is an open LLVM bug for this issue. Take advantage of that section for this config as well so that there are no more orphan warnings. Link: https://bugs.llvm.org/show_bug.cgi?id=46478 Link: https://github.com/ClangBuiltLinux/linux/issues/1069 Reported-by: kernel test robot <[email protected]> Signed-off-by: Nathan Chancellor <[email protected]>Reviewed-by: Nick Desaulniers <[email protected]> I suspect we're going to need to add module level attributes in LLVM IR for these options, then check those when synthesizing new function definitions within LLVM. At least we'll be able to point to this file and say "hey, this is a general problem in LLVM, and here are 3 specific cases now where it's a problem." Not a large problem, but would help us save some bytes in the final object. LLVM is not producing data in this section for all code, just these synthesized routines.
Maybe. There are also a long list of security features which may impose additional requirements. Adding a module flag metadata for each such feature will be a long battle. For .eh_frame, I think it is important/generic enough and can benefit other applications that deserves special handling (and I can look into it). For .init_array, I am not too sure....
--- include/asm-generic/vmlinux.lds.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index b2b3d81b1535..f753fd449436 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -988,12 +988,13 @@ #endif /* - * Clang's -fsanitize=kernel-address and -fsanitize=thread produce + * Clang's -fsanitize=kernel-address, -fsanitize=thread, + * and -fprofile-arcs -ftest-coverage produce unwanted * unwanted sections (.eh_frame and .init_array.*), but * CONFIG_CONSTRUCTORS wants to keep any .init_array.* sections. * https://bugs.llvm.org/show_bug.cgi?id=46478 */ -#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN) +#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN) || defined(CONFIG_GCOV_KERNEL) # ifdef CONFIG_CONSTRUCTORS # define SANITIZER_DISCARDS \ *(.eh_frame) base-commit: bec4c2968fce2f44ce62d05288a633cd99a722eb -- 2.30.0
Drop -ftest-coverage. -ftest-coverage just produces .gcno and does not affect code generation. Reviewed-by: Fangrui Song <[email protected]>
