Exception handling does not work

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DabiiXqx
Posts: 11
Joined: Sun Feb 15, 2026 12:06 am
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Exception handling does not work

Post by DabiiXqx »

Hi everyone, this issue is something i've been struggling to figure out, It's about the ISRs not being called even after setting them and hooking them into the IDT,

I'm in i386 protected mode
This is being run in qemu
My OS is a DOS system, doesn't boot from ISO

The CPU immediately triple faults when encountering a #UD exception. i'll give the full log here

Code: Select all

SMM: enter
EAX=00000000 EBX=00000000 ECX=02000000 EDX=02000628
ESI=0000000b EDI=02000000 EBP=06feb010 ESP=00006d5c
EIP=000ebede EFL=00000046 [---Z-P-] 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=     000f6220 00000037
IDT=     000f625e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000044 CCD=ffffffff CCO=EFLAGS
EFER=0000000000000000
SMM: after RSM
EAX=00000000 EBX=00000000 ECX=02000000 EDX=02000628
ESI=0000000b EDI=02000000 EBP=06feb010 ESP=00006d5c
EIP=000ebede EFL=00000046 [---Z-P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
SS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     000f6220 00000037
IDT=     000f625e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000044 CCD=00000000 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=000f7d2d ECX=00001234 EDX=00006cff
ESI=00006cb8 EDI=06ffee71 EBP=00006c78 ESP=00006c78
EIP=00007d2a EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =da80 000da800 ffffffff 008f9300
CS =f000 000f0000 ffffffff 008f9b00
SS =0000 00000000 ffffffff 008f9300
DS =0000 00000000 ffffffff 008f9300
FS =0000 00000000 ffffffff 008f9300
GS =0000 00000000 ffffffff 008f9300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 00000000
IDT=     00000000 000003ff
CR0=00000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000000 CCD=00006c78 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=000f7d2d ECX=00001234 EDX=00006cff
ESI=00006cb8 EDI=06ffee71 EBP=00006c78 ESP=00006c78
EIP=000f7d2d EFL=00000046 [---Z-P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
SS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     000f6220 00000037
IDT=     000f625e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000044 CCD=00000000 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=00007d47 ECX=00005678 EDX=06fffe88
ESI=000e9780 EDI=06ffee71 EBP=00006c78 ESP=00006c78
EIP=000f7d44 EFL=00000012 [----A--] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
SS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     000f6220 00000037
IDT=     000f625e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000008 CCD=00006c64 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=00007d47 ECX=00005678 EDX=06fffe88
ESI=000e9780 EDI=06ffee71 EBP=00006c78 ESP=00006c78
EIP=00007d47 EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =da80 000da800 ffffffff 00809300
CS =f000 000f0000 ffffffff 00809b00
SS =0000 00000000 ffffffff 00809300
DS =0000 00000000 ffffffff 00809300
FS =0000 00000000 ffffffff 00809300
GS =0000 00000000 ffffffff 00809300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 00000000
IDT=     00000000 000003ff
CR0=00000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000004 CCD=00000001 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=000f7d2d ECX=00001234 EDX=000069ff
ESI=000069a2 EDI=06ffee71 EBP=00006962 ESP=00006962
EIP=00007d2a EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =da80 000da800 ffffffff 008f9300
CS =f000 000f0000 ffffffff 008f9b00
SS =0000 00000000 ffffffff 008f9300
DS =0000 00000000 ffffffff 008f9300
FS =0000 00000000 ffffffff 008f9300
GS =ca00 000ca000 ffffffff 008f9300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 00000000
IDT=     00000000 000003ff
CR0=00000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000000 CCD=00006962 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=000f7d2d ECX=00001234 EDX=000069ff
ESI=000069a2 EDI=06ffee71 EBP=00006962 ESP=00006962
EIP=000f7d2d EFL=00000046 [---Z-P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
SS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     000f6220 00000037
IDT=     000f625e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000044 CCD=00000000 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=00007d47 ECX=00005678 EDX=00000005
ESI=00000000 EDI=06ffee71 EBP=00006962 ESP=00006962
EIP=000f7d44 EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
SS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     000f6220 00000037
IDT=     000f625e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000008 CCD=0000694e CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=00007d47 ECX=00005678 EDX=00000005
ESI=00000000 EDI=06ffee71 EBP=00006962 ESP=00006962
EIP=00007d47 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =da80 000da800 ffffffff 00809300
CS =f000 000f0000 ffffffff 00809b00
SS =0000 00000000 ffffffff 00809300
DS =0000 00000000 ffffffff 00809300
FS =0000 00000000 ffffffff 00809300
GS =ca00 000ca000 ffffffff 00809300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 00000000
IDT=     00000000 000003ff
CR0=00000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000000 CCD=00000001 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=000f7d2d ECX=00001234 EDX=000069ff
ESI=0000699c EDI=06ffee71 EBP=0000695c ESP=0000695c
EIP=00007d2a EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =da80 000da800 ffffffff 00809300
CS =f000 000f0000 ffffffff 00809b00
SS =0000 00000000 ffffffff 00809300
DS =0000 00000000 ffffffff 00809300
FS =0000 00000000 ffffffff 00809300
GS =ca00 000ca000 ffffffff 00809300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 00000000
IDT=     00000000 000003ff
CR0=00000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000000 CCD=0000695c CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=000f7d2d ECX=00001234 EDX=000069ff
ESI=0000699c EDI=06ffee71 EBP=0000695c ESP=0000695c
EIP=000f7d2d EFL=00000046 [---Z-P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
SS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     000f6220 00000037
IDT=     000f625e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000044 CCD=00000000 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=00007d47 ECX=00005678 EDX=00000003
ESI=06fd1fb0 EDI=06ffee71 EBP=0000695c ESP=0000695c
EIP=000f7d44 EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
SS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     000f6220 00000037
IDT=     000f625e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000008 CCD=00006948 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=00007d47 ECX=00005678 EDX=00000003
ESI=06fd1fb0 EDI=06ffee71 EBP=0000695c ESP=0000695c
EIP=00007d47 EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =da80 000da800 ffffffff 00809300
CS =f000 000f0000 ffffffff 00809b00
SS =0000 00000000 ffffffff 00809300
DS =0000 00000000 ffffffff 00809300
FS =0000 00000000 ffffffff 00809300
GS =ca00 000ca000 ffffffff 00809300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 00000000
IDT=     00000000 000003ff
CR0=00000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000004 CCD=00000001 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=000f7d2d ECX=00001234 EDX=000069ff
ESI=000069a2 EDI=06ffee71 EBP=00006962 ESP=00006962
EIP=00007d2a EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =da80 000da800 ffffffff 00809300
CS =f000 000f0000 ffffffff 00809b00
SS =0000 00000000 ffffffff 00809300
DS =0000 00000000 ffffffff 00809300
FS =0000 00000000 ffffffff 00809300
GS =ca00 000ca000 ffffffff 00809300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 00000000
IDT=     00000000 000003ff
CR0=00000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000000 CCD=00006962 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=000f7d2d ECX=00001234 EDX=000069ff
ESI=000069a2 EDI=06ffee71 EBP=00006962 ESP=00006962
EIP=000f7d2d EFL=00000046 [---Z-P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
SS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     000f6220 00000037
IDT=     000f625e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000044 CCD=00000000 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=00007d47 ECX=00005678 EDX=00000005
ESI=00000000 EDI=06ffee71 EBP=00006962 ESP=00006962
EIP=000f7d44 EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
SS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     000f6220 00000037
IDT=     000f625e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000008 CCD=0000694e CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=00007d47 ECX=00005678 EDX=00000005
ESI=00000000 EDI=06ffee71 EBP=00006962 ESP=00006962
EIP=00007d47 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =da80 000da800 ffffffff 00809300
CS =f000 000f0000 ffffffff 00809b00
SS =0000 00000000 ffffffff 00809300
DS =0000 00000000 ffffffff 00809300
FS =0000 00000000 ffffffff 00809300
GS =ca00 000ca000 ffffffff 00809300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 00000000
IDT=     00000000 000003ff
CR0=00000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000000 CCD=00000001 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=000f7d2d ECX=00001234 EDX=000069ff
ESI=0000699c EDI=06ffee71 EBP=0000695c ESP=0000695c
EIP=00007d2a EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =da80 000da800 ffffffff 00809300
CS =f000 000f0000 ffffffff 00809b00
SS =0000 00000000 ffffffff 00809300
DS =0000 00000000 ffffffff 00809300
FS =0000 00000000 ffffffff 00809300
GS =ca00 000ca000 ffffffff 00809300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 00000000
IDT=     00000000 000003ff
CR0=00000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000000 CCD=0000695c CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=000f7d2d ECX=00001234 EDX=000069ff
ESI=0000699c EDI=06ffee71 EBP=0000695c ESP=0000695c
EIP=000f7d2d EFL=00000046 [---Z-P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
SS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     000f6220 00000037
IDT=     000f625e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000044 CCD=00000000 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=00007d47 ECX=00005678 EDX=00000003
ESI=06f31fb0 EDI=06ffee71 EBP=0000695c ESP=0000695c
EIP=000f7d44 EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
CS =0008 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
SS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
DS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
FS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
GS =0010 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT=     000f6220 00000037
IDT=     000f625e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000008 CCD=00006948 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=00007d47 ECX=00005678 EDX=00000003
ESI=06f31fb0 EDI=06ffee71 EBP=0000695c ESP=0000695c
EIP=00007d47 EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =da80 000da800 ffffffff 00809300
CS =f000 000f0000 ffffffff 00809b00
SS =0000 00000000 ffffffff 00809300
DS =0000 00000000 ffffffff 00809300
FS =0000 00000000 ffffffff 00809300
GS =ca00 000ca000 ffffffff 00809300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 00000000
IDT=     00000000 000003ff
CR0=00000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000004 CCD=00000001 CCO=EFLAGS
EFER=0000000000000000
Servicing hardware INT=0x08
check_exception old: 0xffffffff new 0x6
     0: v=06 e=0000 i=0 cpl=0 IP=0008:0000901e pc=0000901e SP=0010:0008fff4 env->regs[R_EAX]=0000001f
EAX=0000001f EBX=00009000 ECX=00001f6c EDX=00000000
ESI=00000000 EDI=00000000 EBP=0008fffc ESP=0008fff4
EIP=0000901e EFL=00000006 [-----P-] 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=     00007c4a 00000017
IDT=     001f0000 0000a280
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000010 CCD=0008ffd4 CCO=ADDL
EFER=0000000000000000
check_exception old: 0xffffffff new 0xd
     1: v=0d e=0032 i=0 cpl=0 IP=0008:0000901e pc=0000901e SP=0010:0008fff4 env->regs[R_EAX]=0000001f
EAX=0000001f EBX=00009000 ECX=00001f6c EDX=00000000
ESI=00000000 EDI=00000000 EBP=0008fffc ESP=0008fff4
EIP=0000901e EFL=00000006 [-----P-] 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=     00007c4a 00000017
IDT=     001f0000 0000a280
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000010 CCD=0008ffd4 CCO=ADDL
EFER=0000000000000000
check_exception old: 0xd new 0xd
     2: v=08 e=0000 i=0 cpl=0 IP=0008:0000901e pc=0000901e SP=0010:0008fff4 env->regs[R_EAX]=0000001f
EAX=0000001f EBX=00009000 ECX=00001f6c EDX=00000000
ESI=00000000 EDI=00000000 EBP=0008fffc ESP=0008fff4
EIP=0000901e EFL=00000006 [-----P-] 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=     00007c4a 00000017
IDT=     001f0000 0000a280
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000 
DR6=ffff0ff0 DR7=00000400
CCS=00000010 CCD=0008ffd4 CCO=ADDL
EFER=0000000000000000
check_exception old: 0x8 new 0xd
The github repo containing all my code is in https://github.com/dabiiXqx/DabiiOS.

I've tried debugging with gdb and my idt pointer struct is correct and functional. the stack is valid and mapped at the time of the ud2 instruction (used for isr testing purposes) the first 32 entries of my idt (0-31) properly contain the address to my isr stubs.

If there's documentation, I'll read it, just give me the source.

Any help is appreciated.
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Octocontrabass
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Posts: 6250
Joined: Mon Mar 25, 2013 7:01 pm

Re: Exception handling does not work

Post by Octocontrabass »

DabiiXqx wrote: ↑Fri Feb 20, 2026 12:34 pmI've tried debugging with gdb and my idt pointer struct is correct and functional.
Are you sure?
DabiiXqx wrote: ↑Fri Feb 20, 2026 12:34 pm

Code: Select all

IDT=     001f0000 0000a280
IDTR is filled with nonsense. If your IDT pointer struct is correct, there must be a problem with the code you're using to load IDTR.

For example, you might be using a pointer to the struct as the input operand when you actually want the struct itself as the operand, like this:

Code: Select all

	asm volatile("lidt %0" : : "m" (*idtp));
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DabiiXqx
Posts: 11
Joined: Sun Feb 15, 2026 12:06 am
Libera.chat IRC: dabii

Re: Exception handling does not work

Post by DabiiXqx »

Thank you so much! i didn't know lidt/sidt actually needed the struct itself.
And in the gdb line i was running p/x idtp, so i was talking about the struct's limit and base itself. not about the LIDT or SIDT instruction.
about me saying "it's functional" , that was bad wording, my fault
But either way thank you!
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