Especially for tracing applications, it is convenient to be able to refer to a symbol using a <module name, symbol name> pair and to be able to translate an address into a <nodule mname, symbol name> pair. But that does not work if the module is built into the kernel because the object files that comprise the built-in module implementation are simply linked into the kernel image along with all other kernel object files.
This is especially visible when providing tracing scripts for support purposes, where the developer of the script targets a particular kernel version, but does not have control over whether the target system has a particular module as loadable module or built-in module. When tracing symbols within a module, referring them by <module name, symbol name> pairs is both convenient and aids symbol lookup. But that naming will not work if the module name information is lost if the module is built into the kernel on the target system. Earlier work addressing this loss of information for built-in modules involved adding module name information to the kallsyms data, but that required more invasive code in the kernel proper. This work never did get merged into the kernel tree. All that is really needed is knowing whether a given address belongs to a particular module (or multiple modules if they share an object file). Or in other words, whether that address falls within an address range that is associated with one or more modules. Objects can be identified as belonging to a particular module (or modules) based on defines that are passed as flags to their respective compilation commands. The data found in modules.builtin.modinfo is used to determine what modules are built into the kernel proper. Then, vmlinux.o.map and vmlinux.map can be parsed in a single pass to generate a modules.buitin.ranges file with offset range information (relative to the base address of the associated section) for built-in modules. This file gets installed along with the other modules.builtin.* files. The impact on the kernel build is minimal because everything is done using a single-pass AWK script. The generated data size is minimal as well, (depending on the exact kernel configuration) usually in the range of 500-700 lines, with a file size of 20-40KB (if all modules are built in, the file contains about 8000 lines, with a file size of about 285KB). Changes since v2: - Switched from using modules.builtin.objs to parsing .*.cmd files - Add explicit dependency on FTRACE for CONFIG_BUILTIN_MODULE_RANGES - 1st arg to generate_builtin_ranges.awk is now modules.builtin.modinfo - Parse data from .*.cmd in generate_builtin_ranges.awk - Use $(real-prereqs) rather than $(filter-out ...) - Include modules.builtin.ranges in modules install target Changes since v1: - Renamed CONFIG_BUILTIN_RANGES to CONFIG_BUILTIN_MODULE_RANGES - Moved the config option to the tracers section - 2nd arg to generate_builtin_ranges.awk should be vmlinux.map Kris Van Hees (5): trace: add CONFIG_BUILTIN_MODULE_RANGES option kbuild: generate a linker map for vmlinux.o module: script to generate offset ranges for builtin modules kbuild: generate modules.builtin.ranges when linking the kernel module: add install target for modules.builtin.ranges Luis Chamberlain (1): kbuild: add modules.builtin.objs .gitignore | 2 +- Documentation/dontdiff | 2 +- Documentation/kbuild/kbuild.rst | 5 ++ Makefile | 8 +- include/linux/module.h | 4 +- kernel/trace/Kconfig | 17 ++++ scripts/Makefile.lib | 5 +- scripts/Makefile.modinst | 11 ++- scripts/Makefile.vmlinux | 17 ++++ scripts/Makefile.vmlinux_o | 18 ++++- scripts/generate_builtin_ranges.awk | 149 ++++++++++++++++++++++++++++++++++++ 11 files changed, 228 insertions(+), 10 deletions(-) create mode 100755 scripts/generate_builtin_ranges.awk base-commit: dd5a440a31fae6e459c0d6271dddd62825505361 -- 2.42.0
