sc_trace for sc_bigint<W> when W=1024

[Ness]

Hi,
When I try to trace sc_signal<sc_bigint<W> >  when W=1024 the following program doesn't finish.
However when I try W=1023 and W=1025 the program works as expected.
Could you please help me to debug the case?

Thank you in advance,
Ness

Quote

#include "systemc.h"
#include <iostream>
#include <fstream>

int sc_main ( int argc, char **argv ) {

    sc_signal<sc_bigint<1023> > signal_to_trace;

    sc_start(1, SC_NS);

    sc_trace_file *Tf = sc_create_vcd_trace_file("waves");

    sc_trace(Tf, signal_to_trace, "signal_to_trace");

    sc_start(1, SC_NS);

    sc_close_vcd_trace_file(Tf);
    
    return 0 ;
}

 

[Roman Popov]

I can't reproduce, works fine for sc_bigint<1024> on my side. What compiler and OS do you use? 

[Ness]

I'm running the code in Visual Studio 2015 on a Windows 10 64-bit platform.
SystemC compiler is "SystemC 2.3.3 (Includes TLM)" from Accellera website.

I can do a workaround in my code if this is a problem in my side.

Thanks for the quick response!
Ness

[Roman Popov]

Thanks for reporting this. I've reproduced the issue. On my side (VS 2017) it crashes with heap corruption, instead of hanging. But I think this is the same issue.

I will debug on this evening. 

[Roman Popov]

There is a buffer overflow bug in vcd_sc_signed_trace::write,  someone forgot to reserve a space for null terminator in null-terminated string.

void
vcd_sc_signed_trace::write(FILE* f)
{
    static std::vector<char> compdata(1024), rawdata(1024);
    typedef std::vector<char>::size_type size_t;

    if ( compdata.size() < static_cast<size_t>(object.length()) ) {
        size_t sz = ( static_cast<size_t>(object.length()) + 4096 ) & (~static_cast<size_t>(4096-1));
        std::vector<char>( sz ).swap( compdata ); // resize without copying values
        std::vector<char>( sz ).swap( rawdata );
    }
    char *rawdata_ptr  = &rawdata[0];

    for (int bitindex = object.length() - 1; bitindex >= 0; --bitindex) {
        *rawdata_ptr++ = "01"[object[bitindex].to_bool()];
    }
    *rawdata_ptr = '\0';
    compose_data_line(&rawdata[0], &compdata[0]);

    std::fputs(&compdata[0], f);
    old_value = object;
}

When you have sc_bigint<1024> , 1024 chars in compdata and rawdata are not enough to store 1024 symbols, 
because 1 symbol is required for null terminator assigned here:

*rawdata_ptr = '\0';

It will also fail with sc_bigint<4096>

Can you add + 1 to size of buffer everywhere , rebuild SystemC and rerun your test? :

void
vcd_sc_signed_trace::write(FILE* f)
{
    static std::vector<char> compdata(1024 + 1), rawdata(1024 + 1);
    typedef std::vector<char>::size_type size_t;

    if ( compdata.size() < static_cast<size_t>(object.length()) ) {
        size_t sz = ( static_cast<size_t>(object.length()) + 4096 ) & (~static_cast<size_t>(4096-1));
        sz ++;
...

Same problem also with sc_biguint<1024>.

Thanks for finding this bug! 

[Philipp A Hartmann]

Fix pushed to the public SystemC repository, see https://github.com/accellera-official/systemc/commit/3e4fc6e0e669c727fcbd46100ee1d7ba58ec5894. This fix will be part of a future release of the Accellera reference implementation.

Thanks again for reporting the issue!