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DBVM Global debug (some doubts about code)

 
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Viloresi
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Joined: 02 Feb 2017
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PostPosted: Thu May 21, 2020 4:55 am    Post subject: DBVM Global debug (some doubts about code) Reply with quote

What this piece of code does? Like what's B0 , L0, G0 , B1 ... etc..
Code:

if (DebuggerState.globalDebug)
         {         
            DebugReg6 dr6=debugger_dr6_getValue();
            DebugReg7 dr7=*(DebugReg7 *)&DebuggerState.FakedDebugRegisterState[cpunr()].DR7;

            //real dr6      //fake dr7
            if ((dr6.B0) && (!(dr7.L0 || dr7.G0))) { DbgPrint("setting RF because of B0\n"); ((PEFLAGS)&stackpointer[si_eflags])->RF=1; return 1; } //break caused by DR0 and not expected by the current process, ignore this bp and continue
            if ((dr6.B1) && (!(dr7.L1 || dr7.G1))) { DbgPrint("setting RF because of B1\n"); ((PEFLAGS)&stackpointer[si_eflags])->RF=1; return 1; } //      ...      DR1      ...
            if ((dr6.B2) && (!(dr7.L2 || dr7.G2))) { DbgPrint("setting RF because of B2\n"); ((PEFLAGS)&stackpointer[si_eflags])->RF=1; return 1; }  //      ...      DR2      ...
            if ((dr6.B3) && (!(dr7.L3 || dr7.G3))) { DbgPrint("setting RF because of B3\n"); ((PEFLAGS)&stackpointer[si_eflags])->RF=1; return 1; }  //      ...      DR3      ...
         }



Why is it needed for globaldebug , instead it's not needed without globaldebug?
Also why did you decide to fake dr7 there and not dr6??
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Dark Byte
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PostPosted: Tue May 26, 2020 1:25 am    Post subject: Reply with quote

This code checks if the breakpoint that just got triggered is a breakpoint by the target process or by CE
DR6.B0 is set if the breakpoint is caused by DR0
But if it's set, and the fake (what the target process sees) DR7 didn't have that breakpoint set, ignore it (as it's in the wrong process context)

DR7.L0 and G0 are enabling bits for breakpoints.

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