使用buildroot构建嵌入式系统带来很多方便。buildroot里使用了很多很好的技术,本文是学习使用buildroot遇到的问题及分析,希望对大家也有帮助。
我们查看一个object文件有not stripped和stripped,而buildroot编译出来的目标文件大多是stripped的。
output/build/test/test2 这个binary文件是not stripped
output/target/usr/bin/test2 而这个binary文件是stripped,这是为什么呢?
1, GNU strip command
strip - Discard symbols from object files.
http://man7.org/linux/man-pages/man1/strip.1.html
2, buildroot strip选项
buildroot/Config.in
注意 BR2_STRIP_strip 默认是选中的
config BR2_ENABLE_DEBUG
bool "build packages with debugging symbols"
help
Build packages with debugging symbols enabled. All libraries
and binaries in the 'staging' directory will have debugging
symbols, which allows remote debugging even if libraries and
binaries are stripped on the target. Whether libraries and
binaries are stripped on the target is controlled by the
BR2_STRIP_* options below.
config BR2_STRIP_strip
bool "strip target binaries"
depends on !BR2_PACKAGE_HOST_ELF2FLT
default y
help
Binaries and libraries in the target filesystem will be
stripped using the normal 'strip' command. This allows to save
space, mainly by removing debugging symbols. Debugging symbols
on the target are needed for native debugging, but not when
remote debugging is used.
makemenuconfig 可以看到选项情况
第3行定义 BR2_STRIP_strip ,你的buildroot使能了strip
第4行定义 BR2_STRIP_EXCLUDE_DIRS , test目录是strip的例外目录
3, buildroot strip的执行的准备工作
定义了执行strip时的命令和参数
1)STRIPCMD 和 STRIP_STRIP_DEBUG
定义在文件 buildroot/package/Makefile.in
ifeq ($(BR2_STRIP_strip),y)
STRIP_STRIP_DEBUG := --strip-debug
TARGET_STRIP = $(TARGET_CROSS)strip
STRIPCMD = $(TARGET_CROSS)strip --remove-section=.comment --remove-section=.note
else
TARGET_STRIP = /bin/true
STRIPCMD = $(TARGET_STRIP)
endif
STRIP_STRIP_DEBUG的意义:Remove debugging symbols only.
而 STRIPCMD 会删掉 .comment, .note 2个section
2) STRIP_FIND_CMD
定义在文件 buildroot/Makefile
STRIP_FIND_CMD = find $(TARGET_DIR)
ifneq (,$(call qstrip,$(BR2_STRIP_EXCLUDE_DIRS)))
STRIP_FIND_CMD += \( $(call finddirclauses,$(TARGET_DIR),$(call qstrip,$(BR2_STRIP_EXCLUDE_DIRS))) \) -prune -o
endif
STRIP_FIND_CMD += -type f \( -perm /111 -o -name '*.so*' \)
# file exclusions:
# - libpthread.so: a non-stripped libpthread shared library is needed for
# proper debugging of pthread programs using gdb.
# - ld.so: a non-stripped dynamic linker library is needed for valgrind
# - kernel modules (*.ko): do not function properly when stripped like normal
# applications and libraries. Normally kernel modules are already excluded
# by the executable permission check above, so the explicit exclusion is only
# done for kernel modules with incorrect permissions.
STRIP_FIND_CMD += -not \( $(call findfileclauses,libpthread*.so* ld-*.so* *.ko $(call qstrip,$(BR2_STRIP_EXCLUDE_FILES))) \) -print0
大概解读一下STRIP_FIND_CMD:
查找target目录下,除BR2_STRIP_EXCLUDE_DIRS目录和BR2_STRIP_EXCLUDE_FILES文件以外的,所有可执行的regular文件,或者文件名是*.so的文件
另外 libpthread*.so, ld-*.so, *.ko 也被看做是strip例外文件,注释里有解释。
4, buildroot strip的执行
buildroot/Makefile 有调用strip的语句
target-finalize: $(PACKAGES)
$(STRIP_FIND_CMD) | xargs -0 $(STRIPCMD) 2>/dev/null || true
另外对 libpthread*.so, ld-*.so 执行 Remove debugging symbols only.
# See http://sourceware.org/gdb/wiki/FAQ, "GDB does not see any threads
# besides the one in which crash occurred; or SIGTRAP kills my program when
# I set a breakpoint"
ifeq ($(BR2_TOOLCHAIN_HAS_THREADS),y)
find $(TARGET_DIR)/lib/ -type f -name 'libpthread*.so*' | \
xargs -r $(STRIPCMD) $(STRIP_STRIP_DEBUG)
endif
# Valgrind needs ld.so with enough information, so only strip
# debugging symbols.
find $(TARGET_DIR)/lib/ -type f -name 'ld-*.so*' | \
xargs -r $(STRIPCMD) $(STRIP_STRIP_DEBUG)
至此,你在output/target下看到的binary文件就是stripped的了