Saturday, September 29, 2012

GCC Bug 53812

I was [un]lucky enough to stumble upon a gcc bug recently. I was working on an interpreter for a simple calculator language and in building the jump table for the instructions I was using a construct similar to:

struct Processor {
    bool initialized_;
    std::map< std::string, void* > jump_table;
    Processor () : initialized_(false) {}
    long execute (Program& prog) {
        if (! initialized_) {

            jump_table["+"] = &&block_add;
            jump_table["-"] = &&block_sub;
            jump_table["*"] = &&block_mul;
            jump_table["/"] = &&block_div;
            jump_table[";"] = &&block_end;
            initialized_ = true;
            return execute (prog);
        prog.value (prog.arg (0) + prog.arg (1));
        goto *jump_table[prog.next_op ()];
        prog.value (prog.arg (0) - prog.arg (1));
        goto *jump_table[prog.next_op ()];
        prog.value (prog.arg (0) / prog.arg (1));
        goto *jump_table[prog.next_op ()];
        prog.value (prog.arg (0) * prog.arg (1));
        goto *jump_table[prog.next_op ()];
        return prog.result ();

Trying to compile that with g++ 4.6.3 leads to the following error: In member function 'long int Processor::execute(Program&)'; internal compiler error: in lower_stmt, at gimple-low.c:432

This bug also manifests itself in 4.7.0 and 4.7.1 but in a another location (verify_gimple_stmt). The oldest copy of gcc I have is 4.3.2 and the bug is not evident in that version.

Granted I was using non-standard constructs in my code but it still felt pretty cool to uncover a bug in such a well-known piece of software.

You can find the bug report (and current status) here

No comments :

Post a Comment