CODEWITHSUNDEEP
cgcclinkermingwatexit
Toby
Toby

Reputation: 3905

MinGW GCC - undefined reference to `atexit'

I am trying to link a large project with GCC 4.8.1 from MinGW for a x86 target. I am calling the linker like this

D:\MyGCCPath\gcc -L [LIBPATHS]  -nostdlib -Wl,-Map,D:\PathToMapFile.map,--emit-relocs [OBJECTFILES AND LIBS] -lmsvcrt -lgcc -o D:\PathToMyOutputFile

With this call I get this linker rror:

libgcc.a(__main.o):(.text+0x5a): undefined reference to `atexit'

I tried different msvcr versions (100 and 90), but this was more a desperate attempt, since I am not very familiar with this problem. I am using the correct libraries provided by MinGW. Is there any way I can fix this error?

Upvotes: 0

Views: 4595

Answers (3)

Zaaier
Zaaier

Reputation: 736

The reasoning in your comment chain with Yu Hao is completely correct.

You need to import libmsvcr120.a with -lmsvcr120 to get the atexit symbol.

You may also need some of these, depending on what symbols you reference, but this is speculation based on very briefly grepping through the source code in clang/lib/Driver/ToolChains for the string OPT_nostdlib:

  • lgcc_eh
  • lgcc_s
  • lgcc
  • lgomp
  • liomp5md
  • lmingw32
  • lmingwex
  • lmingwthrd
  • lmoldname
  • lmsvcr100
  • lmsvcr110
  • lmsvcr80
  • lmsvcr90
  • lmsvcrt-os
  • lomp
  • lssp_nonshared
  • lssp

In general, you can find which libraries contain the symbols you're looking for by calling MinGW's nm.exe (or GNU nm on Linux) on all of the libraries you have (in x86_64-w64-mingw32\lib for example), and piping the output to a text file. You'll get a few hundred thousand lines of text like this that you can search through:

libmsvcr120_defs01591.o:
0000000000000000 b .bss
0000000000000000 d .data
0000000000000000 i .idata$4
0000000000000000 i .idata$5
0000000000000000 i .idata$6
0000000000000000 i .idata$7
0000000000000000 t .text
0000000000000000 I __imp_atexit
                 U _head_lib64_libmsvcr120_def_a
0000000000000000 T atexit

The T atexit (uppercase T) denotes the symbol being exported, with its definition in the .text section.

If you see U atexit, that means "I don't know where atexit is, but it's needed here". If an import library only contains lines with U atexit, then the definition is not in that import library.

You'll notice atexit also defined by libmsvcr120d.a, which is the debug version of libmsvcr120.a, and defined by libmsvcr120_app.a, which is (from what I gather) the version you would link against when distributing an executable on the Windows App Store.

Upvotes: 0

Timothy Baldwin
Timothy Baldwin

Reputation: 3675

Libraries are checked in the order used on the command line so use -lgcc -lmsvcrt.

Upvotes: 0

Yu Hao
Yu Hao

Reputation: 122463

You are linking with -nostdlib, and atexit() is a function from stdlib.h.

According to GCC Link Options:

-nostdlib

Do not use the standard system startup files or libraries when linking. No startup files and only the libraries you specify are passed to the linker, and options specifying linkage of the system libraries, such as -static-libgcc or -shared-libgcc, are ignored.

Upvotes: 4

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