gcov kernel profiling works by emulating parts of GCC's libgcov in the kernel, including a definition of struct gcov_info used by profiling code to handle coverage data. The original definition of this data type is not available outside of GCC's source tree, and when it changes with new GCC versions the result may be hard-to-debug kernel failures [1].
This patch adds a compile-time check to ensure that the kernel's version of struct gcov_info has the same length as the one used by GCC as determined by looking at GCC's assembler output. This check should help reduce the number of run-time failures when using gcov kernel support with new GCC versions that include updates to struct gcov_info. Tested with various GCC versions between 4.9 and 10, and also Clang 11. [1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1891288 Signed-off-by: Peter Oberparleiter <ober...@linux.ibm.com> --- kernel/gcov/Makefile | 9 +++++++++ kernel/gcov/gcc_4_7.c | 3 +++ kernel/gcov/geninfosize.sh | 19 +++++++++++++++++++ 3 files changed, 31 insertions(+) create mode 100755 kernel/gcov/geninfosize.sh diff --git a/kernel/gcov/Makefile b/kernel/gcov/Makefile index 16f8ecc7d882..1cbeb0de944e 100644 --- a/kernel/gcov/Makefile +++ b/kernel/gcov/Makefile @@ -1,6 +1,15 @@ # SPDX-License-Identifier: GPL-2.0 ccflags-y := -DSRCTREE='"$(srctree)"' -DOBJTREE='"$(objtree)"' +ifeq ($(CONFIG_CC_IS_GCC),y) + GCOV_INFO_SIZE := $(shell $(srctree)/$(src)/geninfosize.sh) + ifneq ($(GCOV_INFO_SIZE),) + ccflags-y += -DGCC_GCOV_INFO_SIZE=$(GCOV_INFO_SIZE) + else + $(error Could not determine size of GCC's struct gcov_info) + endif +endif + obj-y := base.o fs.o obj-$(CONFIG_CC_IS_GCC) += gcc_base.o gcc_4_7.o obj-$(CONFIG_CC_IS_CLANG) += clang.o diff --git a/kernel/gcov/gcc_4_7.c b/kernel/gcov/gcc_4_7.c index c53408a00d0b..fce003cfc790 100644 --- a/kernel/gcov/gcc_4_7.c +++ b/kernel/gcov/gcc_4_7.c @@ -94,6 +94,9 @@ struct gcov_info { struct gcov_fn_info **functions; }; +_Static_assert(sizeof(struct gcov_info) == GCC_GCOV_INFO_SIZE, + "struct gcov_info must be updated"); + /** * gcov_info_filename - return info filename * @info: profiling data set diff --git a/kernel/gcov/geninfosize.sh b/kernel/gcov/geninfosize.sh new file mode 100755 index 000000000000..c05f1374fcb3 --- /dev/null +++ b/kernel/gcov/geninfosize.sh @@ -0,0 +1,19 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# +# Determine size of GCC's internal struct gcov_info. CC must be set correctly. +# +# Note: GCC adds an instance of its built-in version of struct gcov_info under +# the label .LPBX0 to assembler output when compiling with --coverage +# + +echo "void fn(void) {}" | $CC -S --coverage -x c - -o - | \ +while read a b c ; do + # .size .LPBX0, 112 + if [ "$a" = ".size" -a "$b" = ".LPBX0," ] ; then + echo "$c" + break + fi +done + +exit 0 -- 2.25.1
