c++
I'm trying to reduce the size of my elf executable. I'm compiling with -ffunction-sections -fdata-sections and linking with -gc-sections , but it appears some of the symbols that I believe are unused are not being discarded.
Is there some command in the GNU toolchain I can run to find out which symbols are being used and where?
Here are my typical build flags:
Compilation: arm-none-eabi-g++.exe -Wall -O3 -mthumb -std=c++11 -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp -fsingle-precision-constant -ffunction-sections -fdata-sections
Link: arm-none-eabi-g++.exe -static -mthumb -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp -Wl,-gc-sections -Wl,-T"LinkerScript.ld
Thanks for the help.
使用交叉引用输出创建链接器映射文件：
-Wl,-Map=output.map -Wl,--cref
I wasn't able to find a command that showed the symbol dependencies. However, I was able to get the information I needed by using the following technique:
/DISCARD/ section of the linker script. This will output an error message revealing which symbol is using it. It looks something like this: <symbol0>' referenced in section '<symbol1>' of <lib0.a file path>(<object0 file path>): defined in discarded section '<symbol0>' of <lib1.a file path>(object1 file path>) /DISCARD/ section until you find the root of the problem. The root of the problem for me was having a class that inherited from another. This created a virtual table, and the compiler cannot remove dead code that is referenced in a virtual table.
Lesson learned: if you want to reduce code size and still use C++, don't use inheritance. The GNU toolchain used to have a -fvtable-gc switch to help with this, but it was removed some time ago. I will refactor my code to address my specific problem.
You can try the linker option -Wl,--trace-symbol=<symbol_name> . It will display in the output where the symbol is defined, and where the symbol is used.
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