How to debug GCC/LD linking process for STL/C++
c++, embedded, gcc, linker, stl
Solution
Using GCC's `-v` and `-Wl,-v` options will show you the linker commands (and version info of the linker) being used.
Which version of GCC are you using? I made some changes for GCC 4.6 (see PR 44647 and PR 43863) to reduce code size to help embedded systems. There's still an outstanding enhancement request (PR 43852) to allow disabling the inclusion of the IO symbols you're seeing - some of them come from the verbose terminate handler, which prints a message when the process is terminated with an active exception. If you're not using execptions then some of that code is useless to you.
Problem
I'm working on a bare-metal cortex-M3 in C++ for fun and profit. I use the STL library as I needed some containers. I thought that by simply providing my allocator it wouldn't add much code to the final binary, since you get only what you use. I actually didn't even expect any linking process at all with the STL (giving my allocator), as I thought it was all template code. I am compiling with `-fno-exception` by the way. Unfortunately, about 600KB or more are added to my binary. I looked up what symbols are included in the final binary with nm and it seemed a joke to me. The list is so long I won't try and past it. Although there are some weak symbols. I also looked in the .map file generated by the linker and I even found the scanf symbols ``` .text 0x000158bc 0x30 /CodeSourcery/Sourcery_CodeBench_Lite_for_ARM_GNU_Linux/bin/../arm-none-linux-gnueabi/libc/usr/lib/libc.a(sscanf.o) 0x000158bc __sscanf 0x000158bc sscanf 0x000158bc _IO_sscanf ``` And: ``` $ arm-none-linux-gnueabi-nm binary | grep scanf 000158bc T _IO_sscanf 0003e5f4 T _IO_vfscanf 0003e5f4 T _IO_vfscanf_internal 000164a8 T _IO_vsscanf 00046814 T ___vfscanf 000158bc T __sscanf 00046814 T __vfscanf 000164a8 W __vsscanf 000158bc T sscanf 00046814 W vfscanf 000164a8 W vsscanf ``` How can I debug this? For first I wanted to understand what exactly GCC is using for linking (I'm linking through GCC). I know that if symbol is found in a text segment, the whole segment is used, but still that's too much. Any suggestion on how to tackle this would really be appreciated. Thanks