[Qemu-devel] Trouble with adding TCG branch instructions

[Soumyadeep Ghosh]

Hi,

I am trying to modify the translate.c file for ARM target to add some extra 
operations for every add/subtract instruction in the target code. Following are 
the main modifications I need to make:

1. Added new registers to CPUArmState and added corresponding TCG registers 
(already done)
2. For every add/subtract, compare the values of the operands, and store the 
greater operand in one of the newly added registers.

For 2, I have added the following sequence of code (with my interpretation of 
the code I have written as comments):

        int label_rn = gen_new_label();
        int label_done = gen_new_label();
        tcg_gen_brcond_tl (TCG_cond_LT, tmp2, tmp, label_rn);      // If tmp2 < 
 tmp, branch to label_rn
        store_reg (s, 20, tmp2);                                                
                    // Store tmp2 in one of the newly added registers
        tcg_gen_br (label_done);                                                
                    // Branch to end
        gen_set_label (label_rn);                                               
                    // Set label_rn to the current code location
        store_reg (s, 20, tmp);                                                 
                    // Store tmp in one of the newly added registers
        gen_set_label (label_done);                                             
            // Set label_done to the current code location
        // Rest of the program

When I try to emulate my ARM program using the compiled version of the modified 
emulator, I get an error (Uncaught signal 11). Debugging with gdb tells me that 
the following assertion on line 1885 of tcg/tcg.c (the function 
tcg_reg_alloc_op) raises the signal:

        assert (ts->val_type == TEMP_VAL_REG);

Does anyone have any insight into what is causing the problem? 

Thanks in advance for any inputs,

Deep