链接期间的GCC标志

Question

Is there any situation in which flags such as -ansi, -Wall, and -pedantic might be relevant during the linking part of the process?

What about the -O optimization flags? Are they only relevant during the compile steps or are they also relevant during linking?

Thanks!

Answer 1

In practice, no - but in theory, -ansi is a dialect option, so it could conceivably affect linking. I've seen similar behaviour with older versions of clang that use libc++ or libstdc++, when using C++11 or C++03 respectively. I find it easier to put these flags in the CC variable: CC = gcc -std=c99 or CC = gcc -std=c90 (ansi).

I just invoke C++ (or C) with $CXX or $CC out of habit. And they are passed by default to configure scripts.

I'm not aware of this being an issue with C, as long as the ABI and calling conventions haven't changed. C++, on the other hand, requires changes to the C++ runtime to support new language features. In either case, it's the compiler that invokes the linker with the relevant libraries.

Answer 2

There is link-time optimization in gcc:

   -flto[=n]
       This option runs the standard link-time optimizer.  When invoked
       with source code, it generates GIMPLE (one of GCC's internal
       representations) and writes it to special ELF sections in the
       object file.  When the object files are linked together, all the
       function bodies are read from these ELF sections and instantiated
       as if they had been part of the same translation unit.

       To use the link-time optimizer, -flto needs to be specified at
       compile time and during the final link.