-gc-sections丢弃使用的数据 [英] -gc-sections discards used data

问题描述

使用avr-gcc，avr-ld

Using avr-gcc, avr-ld

我试图通过使用fdata-sections -ffunction-sections和gc-sections来严重减小输出文件的大小.当不使用这些选项进行编译时，我的输出为〜63KB，而使用这些选项则为〜30KB，所以看起来很棒.

I'm attempting to severely reduce the size of the output file by using fdata-sections -ffunction-sections and gc-sections. When compiled without these options I have an output of ~63KB, and with these options its ~30KB, so it seems great.

不幸的是，在加载并测试了输出之后，我注意到它无法正常工作.垃圾回收似乎已远远超出了我的预期，并且检查.map时发现有些关键数据不存在.

Unfortunately, after loading and testing the output I notice it doesn't work correctly. Garbage collection seems to have removed far more than I expected, and examining the .map I notice some key data is nonexistent.

关于链接时什么导致这些数据/功能被丢弃的任何想法? (我意识到这可能对我提供的详细信息太过希望，如果需要任何信息，请询问，我会尽力提供)

Any idea on what at link time is causing these data/functions to be discarded? (I realize this may be too hopeful of a question with how little detail I provided, if any information is needed please ask and I'd do my best to provide it)

是否有一种方法可以跟踪垃圾回收中未使用的符号?

Is there a way to trace what symbols were tossed by garbage collection as they were "unused"?

如果不使用-fdata-sections -ffunction-sections -gc-sections，是否可以跟踪符号依赖关系? (要验证gc-sections仅收集了应该收集的内容) -我注意到这这是一个选择，但这非常使用Verax建议的方法对我来说很痛苦

Without using -fdata-sections -ffunction-sections -gc-sections, can I trace a symbol dependencies? (To verify gc-sections only collected what it should) - I noticed this this as an option, but it would be very painful for me to use the method suggested by Verax

编译器和链接器行

avr-ld -mavrxmega6 -gc-sections -T 链接描述文件 文件 libgcc.a -o firmware.elf

avr-ld -mavrxmega6 -gc-sections -Tlinkerscript files libgcc.a -o firmware.elf

avr-gcc -Wall -Wstrict原型-g -ffunction-sections -fdata-sections -Os -mmcu = atxmega256a3 -fno-jump-tables -std = gnu99 -fpack-struct -fno-common -mcall-prologues -c -o file.o file.c

avr-gcc -Wall -Wstrict-prototypes -g -ffunction-sections -fdata-sections -Os -mmcu=atxmega256a3 -fno-jump-tables -std=gnu99 -fpack-struct -fno-common -mcall-prologues -c -o file.o file.c

推荐答案

有一个非常明显的ld选项，称为-print-gc-sections，用于检查被扔掉的东西.

There was a pretty obvious ld option called -print-gc-sections to review what is being tossed out.

我从来没有找到一种跟踪符号依赖关系的方法，但最终不需要查看-print-gc-sections.

I never found a way to trace dependencies on a symbol, but ended up not needing to with reviewing -print-gc-sections.

我发现此描述了魔术部分"，我想这与我所看到的相似.有许多自定义链接器节的用法不正确，我使用KEEP来防止这些错误，尽管我确定现在没有删除无效代码，但这可能是我能做到的.

I found this that described "magic sections" and I imagine this is similar to what I was seeing. There were many custom linker sections that were discared incorrectly, I used KEEP to prevent gc of these although I'm sure there is dead code not being removed now, but this may be the best I can do.

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