How to link assembled object? (lack of underscore causes `undefined reference')

[oset jan]

Hello.

I found this md5 implementation in assembly and tried to test it. So I compiled and got error. So then I tried to compile files separately without linking and it went well but linking thrown error again:

$ make md5-test-fast-x86  
gcc -c -std=c99 -O2 md5-test.c
gcc -c -O1 md5-fast-x86.S
gcc  -o md5-test-fast-x86 md5-test.o md5-fast-x86.o
md5-test.o:md5-test.c:(.text+0x4d): undefined reference to `md5_compress'
md5-test.o:md5-test.c:(.text+0xd5): undefined reference to `md5_compress'
md5-test.o:md5-test.c:(.text+0x13a): undefined reference to `md5_compress'
D:/.../mingw32-8.1.0/.../ld.exe: md5-test.o: bad reloc address 0x130 in section `.rdata'ect and there is 
D:/.../mingw32-8.1.0/.../ld.exe: final link failed: Invalid operation
collect2.exe: error: ld returned 1 exit status
Makefile:45: recipe for target 'md5-test-fast-x86' failed
make: *** [md5-test-fast-x86] Error 1

I testes it under linux and it works without any such errors
First I thought it was something wrong with ld.exe: md5-test.o: bad reloc address 0x130 in section '.rdata' but soon I realised it's undefined reference that matters. So I chceked obj and there is md5_compress method so I don't get why it won't link. Then I checked C vesion of the same routine and it linked, no problem. So again I checked and there is _md5_compress exported in it.

Now, I guess, compiler adds underscore to compiled function name/s but why it won't add it to assembled version? And how to add it so it links?

[Sam Tansy]

I took a look at it and there is no prefixed underscore in assembled object.

$ nm md5-test.o md5-fast-x86.o 

md5-test.o:
00000000 b .bss
00000000 d .data
(...)
00000000 t .text
         U ___main
         U _calloc
(...)
00000000 T _main
         U _md5_compress ; <- that is what is "expected" in main()
00000000 T _md5_hash
         U _memcmp
(...)

md5-fast-x86.o:
00000000 b .bss
00000000 d .data
00000000 t .text
00000000 T md5_compress ; <- that is what is provided in md5-fast-x86.o

You could try to add -fleading-underscore as option to gcc but despite the claim in documentation it doens't work, I tell you that.
You could add something to force adding leading underscore to name of the function in md5-fast-x86.S, like this:

#if defined(_WIN32)
# define cdecl(tok) _##tok
#else
# define cdecl(tok) tok
#endif

$ gcc -c -o  md5-fast-x86_.o  md5-fast-x86_.S
$ nm  md5-fast-x86_.o

00000000 b .bss
00000000 d .data
00000000 t .text
00000000 T _md5_compress

Hope it solves the problem.

[Kai Tietz]

Hello,

well, you can build shared libraries exporting symbols without the
32-bit ABI's leading underscore ... see here for reference the ld
tool's option for more detail. Nevertheless the import-library for
such a shared object (DLL) will contain the leading underscores. You
will need to use a definition file to create it, or you can link
directly to the DLL ... if you have headers, which properly define the
export's calling-convetion.

Hope that helps
Kai

Am So., 24. Mai 2020 um 18:18 Uhr schrieb Sam Tansy
tansy@users.sourceforge.net:

I took a look at it and there is no prefixed underscore in assembled object.

$ nm md5-test.o md5-fast-x86.o

md5-test.o:
00000000 b .bss
00000000 d .data
(...)
00000000 t .text
U ___main
U _calloc
(...)
00000000 T _main
U _md5_compress ; <- that is what is "expected" in main()
00000000 T _md5_hash
U _memcmp
(...)

md5-fast-x86.o:
00000000 b .bss
00000000 d .data
00000000 t .text
00000000 T md5_compress ; <- that is what is provided in md5-fast-x86.o

You could try to add -fleading-underscore as option to gcc but despite the claim in documentation it doens't work, I tell you that.
You could add something to force adding leading underscore to name of the function in md5-fast-x86.S, like this:

if defined(_WIN32)

define cdecl(tok) _##tok

else

define cdecl(tok) tok

endif

$ gcc -c -o md5-fast-x86_.o md5-fast-x86_.S
$ nm md5-fast-x86_.o

00000000 b .bss
00000000 d .data
00000000 t .text
00000000 T _md5_compress

Hope it solves the problem.

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How to link assembled object? (lack of underscore causes `undefined reference')

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[oset jan]

Thanks for advice. I have tested it and it works. Not a perfect solution but works. Unluckily '-fleading-underscore' indeed doesn't work.

And when comes to dll, thank you as well but it's just 1.6k of code. It meant to be included.