如何覆盖链接器的默认gcc选项？

Question

在我的系统上编译时（使用bfin-linux-uclibc-g++，但这是无关紧要的），我得到了数百个关于其中一个编译器标志的警告（不在我自己的代码库中）。我想禁用它。

fde encoding in src/SpiMessageUtil.o(.eh_frame) prevents .eh_frame_hdr table being created.

这是从默认的gcc标志开始的，该标志被移交给链接器，通过将'-v'添加到编译步骤中很容易检查：

COLLECT_GCC_OPTIONS=... --eh-frame-hdr ...

我想摆脱这个选项，这确实是默认定义的：

bfin-linux-uclibc-g++ -dumpspecs | grep frame-hdr
%{!static:--eh-frame-hdr}\
%{mfdpic: -m elf32bfinfd -z text} %{shared} %{pie}   \
%{static:-dn -Bstatic}   %{shared:-G -Bdynamic}   \
%{!shared: %{!static:    %{rdynamic:-export-dynamic}    \
  %{!dynamic-linker:-dynamic-linker \
     %{mglibc:%{muclibc:%e-mglibc and -muclibc used together;:%e-mglibc not supported for this target};:/lib/ld-uClibc.so.0 \
}}}\
%{static}} -init __init -fini __fini

如何覆盖此选项？我不能使用-Wl,--no-eh-frame-hdr，因为没有任何类似的定义。

Answer 1

I just got started with back-porting some code to an old system with a bfin controller and ran into the problem with these terribly annoying warnings - 1000s at a time. I didn't find a way to just deactivate the output.

But there are 2 "ways to go" that work:

Fix the source and rebuild the tool-chain:

Remove the code that creates the output in elf-eh-frame.c in the function _bfd_elf_discard_section_eh_frame:

(*info->callbacks->einfo)
    (_("%P: fde encoding in %B(%A) prevents .eh_frame_hdr"
       " table being created.\n"), abfd, sec);

Patch the ld binary

Take a look at the ld-Binary and patch the binary directly. I dumped the data segment (.rodata) with objdump to find the address of the string. Then (after creating a disassembly with objdump) I searched where that string was used and replaced the call to the function that creates the output with two NoOps (0xFF 0xD3 -> 0x90 0x90). Linker still creates the same output, but no more messages.

Answer 2

您可以动态转储GCC的规范，从那里删除此开关并在链接时使用它，即：

g++ -dumpspecs | sed -e 's,--eh-frame-hdr,,g' > better_specs
g++ -specs=better_specs -o target file1.o file2.o -llib1...

这将替换内联规范，同时保持原始编译器的完整。

如果您保留自己的Makefile，也可以使用以下内容处理：

$(TARGET): $(OBJS) | better_specs
    $(LINK.o) $(OUTPUT_OPTION) -specs=$| $^

better_specs:
    $(CXX) -dumpspecs | sed -e 's,--eh-frame-hdr,,g' > $@

这种方法也可以用于配置脚本，只要你以前生成better_specs，就可以使用./configure CXX='g++ -specs=/path/to/better_specs'。