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| Task switching issues https://forum.osdev.org/viewtopic.php?f=1&t=56017 |
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| Author: | iProgramInCpp [ Fri Dec 03, 2021 11:51 am ] |
| Post subject: | Task switching issues |
Hi! I've restarted development of my OS (with the bare minimum of features) and I kind of need help again with task switching. It crashes randomly unless I push the task switching asm code 400kb using a resb (Probably some invalid address its using) Source: https://github.com/iProgramMC/OSProject Here's what I get Code: Triple fault CPU Reset (CPU 0) EAX=001026fe EBX=001c6c64 ECX=00205ecc EDX=0000012b ESI=0000020f EDI=000b851a EBP=00205f4c ESP=001026fe EIP=00102717 EFL=00000016 [----AP-] CPL=0 II=0 A20=1 SMM=0 HLT=0 ES =0010 00000000 ffffffff 00cf9300 DPL=0 DS [-WA] CS =0008 00000000 ffffffff 00cf9a00 DPL=0 CS32 [-R-] SS =0010 00000000 ffffffff 00cf9300 DPL=0 DS [-WA] DS =0010 00000000 ffffffff 00cf9300 DPL=0 DS [-WA] FS =0010 00000000 ffffffff 00cf9300 DPL=0 DS [-WA] GS =0010 00000000 ffffffff 00cf9300 DPL=0 DS [-WA] LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy GDT= 00102630 00000017 IDT= 00106040 00000800 CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000 DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 DR6=ffff0ff0 DR7=00000400 CCS=00000008 CCD=00205ed4 CCO=ADDL EFER=0000000000000000 FCW=037f FSW=0000 [ST=0] FTW=00 MXCSR=00001f80 FPR0=0000000000000000 0000 FPR1=0000000000000000 0000 FPR2=0000000000000000 0000 FPR3=0000000000000000 0000 FPR4=0000000000000000 0000 FPR5=0000000000000000 0000 FPR6=0000000000000000 0000 FPR7=0000000000000000 0000 XMM00=00000000000000000000000000000000 XMM01=00000000000000000000000000000000 XMM02=00000000000000000000000000000000 XMM03=00000000000000000000000000000000 XMM04=00000000000000000000000000000000 XMM05=00000000000000000000000000000000 XMM06=00000000000000000000000000000000 XMM07=00000000000000000000000000000000 Triple fault CPU Reset (CPU 0) EAX=000f5e06 EBX=00000000 ECX=00000000 EDX=00000cf9 ESI=00000000 EDI=00100000 EBP=00000000 ESP=00000fb4 EIP=000f1732 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0 ES =0010 00000000 ffffffff 00cf9300 DPL=0 DS [-WA] CS =0008 00000000 ffffffff 00cf9b00 DPL=0 CS32 [-RA] SS =0010 00000000 ffffffff 00cf9300 DPL=0 DS [-WA] DS =0010 00000000 ffffffff 00cf9300 DPL=0 DS [-WA] FS =0010 00000000 ffffffff 00cf9300 DPL=0 DS [-WA] GS =0010 00000000 ffffffff 00cf9300 DPL=0 DS [-WA] LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy GDT= 000f5e80 00000037 IDT= 000f5ebe 00000000 CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000 DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 DR6=ffff0ff0 DR7=00000400 CCS=000f5ec8 CCD=0000a134 CCO=SUBL EFER=0000000000000000 FCW=037f FSW=0000 [ST=0] FTW=00 MXCSR=00001f80 FPR0=0000000000000000 0000 FPR1=0000000000000000 0000 FPR2=0000000000000000 0000 FPR3=0000000000000000 0000 FPR4=0000000000000000 0000 FPR5=0000000000000000 0000 FPR6=0000000000000000 0000 FPR7=0000000000000000 0000 XMM00=00000000000000000000000000000000 XMM01=00000000000000000000000000000000 XMM02=00000000000000000000000000000000 XMM03=00000000000000000000000000000000 XMM04=00000000000000000000000000000000 XMM05=00000000000000000000000000000000 XMM06=00000000000000000000000000000000 XMM07=00000000000000000000000000000000 and I can see that's on the iretd instruction |
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| Author: | iProgramInCpp [ Mon Dec 06, 2021 8:48 am ] |
| Post subject: | Re: Task switching issues |
Looked into the issue a bit more but I still can't find the error. I'm kind of lost right now |
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| Author: | iProgramInCpp [ Mon Dec 06, 2021 11:14 am ] |
| Post subject: | Re: Task switching issues |
Ok, I tracked down the issue. You see, in task.c I have a variable named CPUSaveState* g_saveStateToRestore = NULL; that I use in RestoreKernelTask. Using a debugging tool I have I can find that the address is .bss:29F978. Then I make reference of it in ktask.asm (I use NASM to compile asm files) and the code looks something like this: Code: extern g_saveStateToRestore OnStartedNewTask: OnStartedNewKernelTask: ;cli ; restore the registers now mov esp, [g_saveStateToRestore] The problem is that the value used by the asm's g_saveStateToRestore does NOT have the same address as the one inside the C file. Instead it's been moved 0x100 bytes forward to .bss:29FA78. It's really strange. FYI: The dumps: Code: .bss:0029F978 ; CPUSaveState_0 *g_saveStateToRestore
.bss:0029F978 g_saveStateToRestore dd ? ; DATA XREF: RestoreKernelTask+6↑w .bss:0029F978 ; RestoreStandardTask+C↑w ... (0x100 bytes later) .bss:0029FA78 dword_29FA78 dd ? ; DATA XREF: OnStartedNewTask↑r |
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| Author: | iProgramInCpp [ Mon Dec 06, 2021 12:53 pm ] |
| Post subject: | Re: Task switching issues |
Guess the decompiler was the issue, haha. Anyways I tracked it down to my memory allocator of all things starting allocation too early (at 0x200000, but the kernel bss section went till 0x2A0000). |
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