Re: [libunwind] Linking with libunwind.a using the Intel compiler

[Tommy Hoffner]

Jeremy Suurkivi wrote:

> I'm having trouble linking a test program with libunwind.a using the
> Intel compiler, version 7.1 
>
> I have created a simple test program (shown below) based on the example
> from the docs.  If I try to build using: 
>
> $ ecpc -Iinc test.cpp libunwind.a -o test 
>
> I get the following error: 
>
>  /<part_of_directory_omitted>/71_40_S2/ia64/lib/libunwind.a(unwind.o):
> In function `_Unwind_Resume': 
> unwind.o(.text+0x1300): multiple definition of `_Unwind_Resume' 
> libunwind.a(Resume.o):unwind/Resume.c:30: first defined here 
> ld: Disabling relaxation: it will not work with multiple definitions 
> ld: Warning: size of symbol `_Unwind_Resume' changed from 800 to 3328 in
> /<part_of_directory_omitted>/71_40_S2/ia64/lib/libunwind.a(unwind.o) 
>
> I built libunwind.a (0.98.3) with the same compiler according to the
> steps in README.  I also tried building libunwind using gcc. 
>
> The same command works with version 8 of the Intel compiler or with g++
> substituted for ecpc.
This is due to the fact that Intel has changed default behaviour for the 
compiler somewhere between version 7 and the latest.
7.1 uses the included Dinkumware c++-libraries (and include-files) while 
8.0 (or 8.1?) switched to using the libraries related to the binary 
called gcc in the searchpath (if it is gcc 3.2 or higher)

ecpc file.C in ver 8 is equivalent to ecpc -cxxlib-gcc in 7.1.

And yes the Dinkumware libraries has there own libunwind which has 
nothing to do with this lists libunwind, e.g. Intels compiler does 
definetly not support this libunwind if you link towards the Dinkumware 
libraries.

If and how the gcc libraries (eg gcclib) support libunwind you can 
probably see in my earlier discussion with David.

>  I can also get around this by using dynamic
> linking: 
>
> $ ecpc -Iinc test.cpp -Llib -lunwind -o test 
>
> This seems to be a reasonable solution but I'm still a little nervous
> using it.  It seems that the Intel compiler statically links in its own
> unwind library (libunwind.so.4 in this case) and it seems there is a
> symbol clash with _Unwind_Resume.  Is it safe to substitute
> _Unwind_Resume from one library into the other?  Or to have both of
> these libraries linked in at the same time? 
I doubt it. According to Intel, Mosbergers libunwind is not supported 
yet, but it seems to work when linking with gcc-libraries. I got it 
working for ecpc ver 8.1 and gcc 3.3/3.4 (latest debian sarge) with some 
restrictions (se my earlier posts, there is a makefile with two 
equivalent setups, one using ecpc and one using gcc).

I don't know what platform you are using but I found it none-trivial to 
get dynamic support working for debian sarge on Itanium.
(One feature I was using was broken in the 0.97 releas that comes with 
debian sarge and it was not trivial to get it to use a full functional 
0.98.3, but my probelms where related to duýnamic unwind so it might 
work for you.)

Good luck,

/Tommy
> Thanks, 
>
> Jeremy 
>
>
>
> #define UNW_LOCAL_ONLY 
> #include <libunwind.h> 
> #include <stdio.h> 
>
> void show_backtrace (void) { 
>   unw_cursor_t cursor; unw_context_t uc; 
>   unw_word_t ip, sp; 
>
>   unw_getcontext(&uc); 
>   unw_init_local(&cursor, &uc); 
>   while (unw_step(&cursor) > 0) { 
>     unw_get_reg(&cursor, UNW_REG_IP, &ip); 
>     unw_get_reg(&cursor, UNW_REG_SP, &sp); 
>     printf ("ip = %lx, sp = %lx\n", (long) ip, (long) sp); 
>   } 
> } 
>
> void a(void) 
> { 
>    show_backtrace(); 
>    printf("\n"); 
> } 
>
>
> int main(int argc, char *argv[]) 
> { 
>    a(); 
>
>    return 0; 
> }
>
>
> ------------------------------------------------------------------------
>
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--
Tommy Hoffner
Senior Software Designer
Compiler Technology

Ericsson AB
Development Unit Core Network Development
Tel:    +46 13 23 57 12
Fax:    +46 13 23 57 99
address@hidden
www.ericsson.com

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