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Re: [Tinycc-devel] x86_64, musl: generation of mixed C/C++ fails: undefi

From: Michael Matz
Subject: Re: [Tinycc-devel] x86_64, musl: generation of mixed C/C++ fails: undefined reference to `__va_start'
Date: Thu, 3 Jan 2019 18:03:49 +0100 (CET)
User-agent: Alpine 2.21 (LSU 202 2017-01-01)


On Thu, 3 Jan 2019, Steffen Nurpmeso wrote:

Regardless of whether i use the AlpineLinux default tcc package,
or my version with the little path-resistancy patch, i cannot
create a binary from several C files which become compiled with
tcc -static and linked to an -ar chive, and some C++ files:

 clang -Dsu_USECASE_SU -I../../src -I../../include -Wall -pedantic -o .main.o 
-c .main.cc
 tcc -Dsu_USECASE_SU -I../../src -I../../include -static -g -O1 -Wall -pedantic 
-o avopt.o -c avopt.c
 tcc -ar .clib.a avopt.o core-code.o core-errors.o cs-alloc.o cs-ctype.o 
cs-dict.o cs-find.o cs-misc.o cs-toolbox.o cs-tools.o icodec-dec.o icodec-enc.o 
mem-alloc.o mem-bag.o mem-tools.o prime.o utf.o
 clang  -o .main cxx-core.o .main.o .clib.a
 /usr/bin/ld: .clib.a(core-code.o): in function `su_log_write':
 /home/steffen/src/nail.git/src/su/core-code.c:233: undefined reference to 

The reason is of course that this symbol resides in
/usr/lib/tcc/libtcc1.a, but that is unknown to the linker.
That makes me feel quite dumb, i would not know nothing but
-static in order to address that myself (except for -ar checking
unreferenced symbols for this name, i have never looked into ar(1)
but would not think it goes that far)?

Well, you have to add the TCC support library into the link process. Either by using TCC as linker instead of clang or by explicitely listing it.

That's not different from other compilers, e.g. when compiled by GCC you need to link with libgcc.a (or libgcc_s.so), either by using gcc as link editor or by listing it explicitely. I.e. compilers always come with a support library that implements whatever code is relied upon by their implementation (e.g. for GCC that could be functions for dealing with decimal float numbers), and you need to include those libraries when linking object files produced by those compilers. Usually that's done by using the respective compiler as link editor which automatically adds the support library. Obviously that won't work if you use multiple compilers: you can only choose one as the link editor (you chose clang) and hence have to list the support library of the other one explicitely (libtcc1.a for your case).

You seem to be under the impression that -ar somehow could deal with this: it can't. ar does nothing more than essentially packing all object files you listed into one .a file. In particular no symbol resolution or linking steps are involved, and so the reference to __va_start is left untouched. In this case even listing libtcc.a wouldn't help as ar leaves other archives alone. You would have to unpack libtcc.a and include its individual object files in the tcc -ar command. (But then you can just as well just mention that library in the link editing step later).

I hope this clarifies the problem a bit. In short: you have to list libtcc.a explicitely.


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