Assigning a pointer NULL crashes the kernel.

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ffexl
Posts: 7
Joined: Wed Apr 23, 2025 11:16 pm

Assigning a pointer NULL crashes the kernel.

Post by ffexl »

I am using generic data structures for my OS (double-linked list and an RB-BST specifically). Whenever I try to initialize these data structures, the kernel crashes and LLDB blames a NULL pointer assignment for the cause. Although the structures appear to work somewhat, they inevitably crash whenever they rely on the assumption they were initialized. I have confirmed that these aren't isolated incidents. Whenever I attempt to assign any pointer NULL, it crashes.

Here are some examples of where this would happen

Code: Select all

struct List {
    ListNode *head;
    ListNode *tail;
    size_t size;
};

void list_init(List *list) {
    assert(list);

->  list->head = NULL;
->  list->tail = NULL;
    list->size = 0;
}
and

Code: Select all

struct RBTree {
    int (*compare)(const void *key, const RBTreeNode *node);
    void (*collide)(const RBTreeNode *old_node, const RBTreeNode *new_node, void *auxiliary_data);
    void *auxiliary_data;
    RBTreeNode *root;
    size_t size;
};

void rbtree_init(
    RBTree *rbtree,
    int (*compare)(const void *key, const RBTreeNode *node),
    void (*collide)(const RBTreeNode *old_node, const RBTreeNode *new_node, void *auxiliary_data),
    void *auxiliary_data
) {
    assert(rbtree && compare);

    rbtree->compare = compare;
    rbtree->collide = collide;
    rbtree->auxiliary_data = auxiliary_data;
->  rbtree->root = NULL;
    rbtree->size = 0;
}
As for my environment, I am using Clang and LLD with the LLDB debugger. I am using Limine Bootloader (which initializes the GDT) and am booting directly into x86_64 on QEMU.
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Octocontrabass
Member
Member
Posts: 5868
Joined: Mon Mar 25, 2013 7:01 pm

Re: Assigning a pointer NULL crashes the kernel.

Post by Octocontrabass »

How is NULL defined?
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ffexl
Posts: 7
Joined: Wed Apr 23, 2025 11:16 pm

Re: Assigning a pointer NULL crashes the kernel.

Post by ffexl »

nullptr or NULL from stddef.h (still available in ffreestanding -nostdlib)
Top
Octocontrabass
Member
Member
Posts: 5868
Joined: Mon Mar 25, 2013 7:01 pm

Re: Assigning a pointer NULL crashes the kernel.

Post by Octocontrabass »

Which exception occurs when it crashes?
Top
ffexl
Posts: 7
Joined: Wed Apr 23, 2025 11:16 pm

Re: Assigning a pointer NULL crashes the kernel.

Post by ffexl »

here's a LLDB log

Code: Select all

* thread #1, stop reason = signal SIGQUIT
    frame #0: 0xffffffff800036b5 BaseOS.bin`list_init(list=0xffffffff80008058) at list.c:27:16
   24   void list_init(List *list) {
   25       assert(list);
   26   
-> 27       list->head = (void*)0;
   28       list->tail = (void*)0;
   29       list->size = 0;
   30   }
and a QEMU log with -d int,guest_errors

Code: Select all

SMM: enter
EAX=00000000 EBX=00000000 ECX=02000000 EDX=02000628
ESI=0000000b EDI=02000000 EBP=00014e40 ESP=00006c5c
EIP=000ea61d 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=     000f61e0 00000037
IDT=     000f621e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000000 CCD=ffffffff CCO=CLR
EFER=0000000000000000
SMM: after RSM
EAX=00000000 EBX=00000000 ECX=02000000 EDX=02000628
ESI=0000000b EDI=02000000 EBP=00014e40 ESP=00006c5c
EIP=000ea61d 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=     000f61e0 00000037
IDT=     000f621e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000044 CCD=00000000 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=000f7e0e ECX=00001234 EDX=00006cff
ESI=00006cb4 EDI=11bfec55 EBP=00006c74 ESP=00006c74
EIP=00007e0b EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =d900 000d9000 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=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000000 CCD=00006c74 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=000f7e0e ECX=00001234 EDX=00006cff
ESI=00006cb4 EDI=11bfec55 EBP=00006c74 ESP=00006c74
EIP=000f7e0e 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=     000f61e0 00000037
IDT=     000f621e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000044 CCD=00000000 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=00007e28 ECX=00005678 EDX=11be8ac0
ESI=000e8380 EDI=11bfec55 EBP=00006c74 ESP=00006c74
EIP=000f7e25 EFL=00000016 [----AP-] 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=     000f61e0 00000037
IDT=     000f621e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000008 CCD=00006c60 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=00007e28 ECX=00005678 EDX=11be8ac0
ESI=000e8380 EDI=11bfec55 EBP=00006c74 ESP=00006c74
EIP=00007e28 EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =d900 000d9000 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=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000004 CCD=00000001 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=000f7e0e ECX=00001234 EDX=000069ff
ESI=00006996 EDI=11bfec55 EBP=00006956 ESP=00006956
EIP=00007e0b EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =d900 000d9000 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=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000000 CCD=00006956 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=000f7e0e ECX=00001234 EDX=000069ff
ESI=00006996 EDI=11bfec55 EBP=00006956 ESP=00006956
EIP=000f7e0e 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=     000f61e0 00000037
IDT=     000f621e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000044 CCD=00000000 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=00007e28 ECX=00005678 EDX=00000005
ESI=00000000 EDI=11bfec55 EBP=00006956 ESP=00006956
EIP=000f7e25 EFL=00000016 [----AP-] 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=     000f61e0 00000037
IDT=     000f621e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000008 CCD=00006942 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=00007e28 ECX=00005678 EDX=00000005
ESI=00000000 EDI=11bfec55 EBP=00006956 ESP=00006956
EIP=00007e28 EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =d900 000d9000 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=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000004 CCD=00000001 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=000f7e0e ECX=00001234 EDX=000069ff
ESI=00006990 EDI=11bfec55 EBP=00006950 ESP=00006950
EIP=00007e0b EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =d900 000d9000 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=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000000 CCD=00006950 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=000f7e0e ECX=00001234 EDX=000069ff
ESI=00006990 EDI=11bfec55 EBP=00006950 ESP=00006950
EIP=000f7e0e 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=     000f61e0 00000037
IDT=     000f621e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000044 CCD=00000000 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=00007e28 ECX=00005678 EDX=00000003
ESI=11bcaf60 EDI=11bfec55 EBP=00006950 ESP=00006950
EIP=000f7e25 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=     000f61e0 00000037
IDT=     000f621e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000008 CCD=0000693c CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=00007e28 ECX=00005678 EDX=00000003
ESI=11bcaf60 EDI=11bfec55 EBP=00006950 ESP=00006950
EIP=00007e28 EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =d900 000d9000 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=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000004 CCD=00000001 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=000f7e0e ECX=00001234 EDX=000069ff
ESI=00006996 EDI=11bfec55 EBP=00006956 ESP=00006956
EIP=00007e0b EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =d900 000d9000 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=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000000 CCD=00006956 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=000f7e0e ECX=00001234 EDX=000069ff
ESI=00006996 EDI=11bfec55 EBP=00006956 ESP=00006956
EIP=000f7e0e 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=     000f61e0 00000037
IDT=     000f621e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000044 CCD=00000000 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=00007e28 ECX=00005678 EDX=00000005
ESI=00000000 EDI=11bfec55 EBP=00006956 ESP=00006956
EIP=000f7e25 EFL=00000016 [----AP-] 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=     000f61e0 00000037
IDT=     000f621e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000008 CCD=00006942 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=00007e28 ECX=00005678 EDX=00000005
ESI=00000000 EDI=11bfec55 EBP=00006956 ESP=00006956
EIP=00007e28 EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =d900 000d9000 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=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000004 CCD=00000001 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=000f7e0e ECX=00001234 EDX=000069ff
ESI=00006990 EDI=11bfec55 EBP=00006950 ESP=00006950
EIP=00007e0b EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =d900 000d9000 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=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000000 CCD=00006950 CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=000f7e0e ECX=00001234 EDX=000069ff
ESI=00006990 EDI=11bfec55 EBP=00006950 ESP=00006950
EIP=000f7e0e 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=     000f61e0 00000037
IDT=     000f621e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000044 CCD=00000000 CCO=EFLAGS
EFER=0000000000000000
SMM: enter
EAX=000000b5 EBX=00007e28 ECX=00005678 EDX=00000003
ESI=11b0af60 EDI=11bfec55 EBP=00006950 ESP=00006950
EIP=000f7e25 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=     000f61e0 00000037
IDT=     000f621e 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000008 CCD=0000693c CCO=ADDL
EFER=0000000000000000
SMM: after RSM
EAX=000000b5 EBX=00007e28 ECX=00005678 EDX=00000003
ESI=11b0af60 EDI=11bfec55 EBP=00006950 ESP=00006950
EIP=00007e28 EFL=00000006 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =d900 000d9000 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=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000004 CCD=00000001 CCO=EFLAGS
EFER=0000000000000000
Servicing hardware INT=0x0e
Servicing hardware INT=0x0e
Servicing hardware INT=0x08
Servicing hardware INT=0x0e
Servicing hardware INT=0x0e
Servicing hardware INT=0x0e
Servicing hardware INT=0x0e
Servicing hardware INT=0x08
Servicing hardware INT=0x08
Servicing hardware INT=0x08
Servicing hardware INT=0x08
check_exception old: 0xffffffff new 0x6
     0: v=06 e=0000 i=0 cpl=0 IP=0028:ffffffff800036b5 pc=ffffffff800036b5 SP=0030:ffff800012b9ff38 env->regs[R_EAX]=0000000000000000
RAX=0000000000000000 RBX=ffffffff80008050 RCX=ffffffff80008328 RDX=00000000000003f8
RSI=ffffffff80008050 RDI=ffffffff80008058 RBP=ffff800012b9ff70 RSP=ffff800012b9ff38
R8 =ffffffffffffffff R9 =0000000000000012 R10=0000000000000032 R11=0000000000000000
R12=ffff8000003e3000 R13=ffff800012b1a000 R14=ffffffff80008238 R15=ffffffff80008058
RIP=ffffffff800036b5 RFL=00000082 [--S----] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
CS =0028 0000000000000000 00000000 00209b00 DPL=0 CS64 [-RA]
SS =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
DS =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
FS =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
GS =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
LDT=0000 0000000000000000 00000000 00008200 DPL=0 LDT
TR =0000 0000000000000000 0000ffff 00008b00 DPL=0 TSS64-busy
GDT=     ffff800000014dd8 00000037
IDT=     0000000000000000 00000000
CR0=80010011 CR2=0000000000000000 CR3=0000000012b8f000 CR4=00000020
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000000000000d0 CCD=ffffffff80008058 CCO=LOGICQ
EFER=0000000000000d00
check_exception old: 0xffffffff new 0xd
     1: v=0d e=0032 i=0 cpl=0 IP=0028:ffffffff800036b5 pc=ffffffff800036b5 SP=0030:ffff800012b9ff38 env->regs[R_EAX]=0000000000000000
RAX=0000000000000000 RBX=ffffffff80008050 RCX=ffffffff80008328 RDX=00000000000003f8
RSI=ffffffff80008050 RDI=ffffffff80008058 RBP=ffff800012b9ff70 RSP=ffff800012b9ff38
R8 =ffffffffffffffff R9 =0000000000000012 R10=0000000000000032 R11=0000000000000000
R12=ffff8000003e3000 R13=ffff800012b1a000 R14=ffffffff80008238 R15=ffffffff80008058
RIP=ffffffff800036b5 RFL=00000082 [--S----] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
CS =0028 0000000000000000 00000000 00209b00 DPL=0 CS64 [-RA]
SS =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
DS =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
FS =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
GS =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
LDT=0000 0000000000000000 00000000 00008200 DPL=0 LDT
TR =0000 0000000000000000 0000ffff 00008b00 DPL=0 TSS64-busy
GDT=     ffff800000014dd8 00000037
IDT=     0000000000000000 00000000
CR0=80010011 CR2=0000000000000000 CR3=0000000012b8f000 CR4=00000020
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000000000000d0 CCD=ffffffff80008058 CCO=LOGICQ
EFER=0000000000000d00
check_exception old: 0xd new 0xd
     2: v=08 e=0000 i=0 cpl=0 IP=0028:ffffffff800036b5 pc=ffffffff800036b5 SP=0030:ffff800012b9ff38 env->regs[R_EAX]=0000000000000000
RAX=0000000000000000 RBX=ffffffff80008050 RCX=ffffffff80008328 RDX=00000000000003f8
RSI=ffffffff80008050 RDI=ffffffff80008058 RBP=ffff800012b9ff70 RSP=ffff800012b9ff38
R8 =ffffffffffffffff R9 =0000000000000012 R10=0000000000000032 R11=0000000000000000
R12=ffff8000003e3000 R13=ffff800012b1a000 R14=ffffffff80008238 R15=ffffffff80008058
RIP=ffffffff800036b5 RFL=00000082 [--S----] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
CS =0028 0000000000000000 00000000 00209b00 DPL=0 CS64 [-RA]
SS =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
DS =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
FS =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
GS =0030 0000000000000000 00000000 00009300 DPL=0 DS   [-WA]
LDT=0000 0000000000000000 00000000 00008200 DPL=0 LDT
TR =0000 0000000000000000 0000ffff 00008b00 DPL=0 TSS64-busy
GDT=     ffff800000014dd8 00000037
IDT=     0000000000000000 00000000
CR0=80010011 CR2=0000000000000000 CR3=0000000012b8f000 CR4=00000020
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000 
DR6=00000000ffff0ff0 DR7=0000000000000400
CCS=00000000000000d0 CCD=ffffffff80008058 CCO=LOGICQ
EFER=0000000000000d00
check_exception old: 0x8 new 0xd
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ffexl
Posts: 7
Joined: Wed Apr 23, 2025 11:16 pm

Re: Assigning a pointer NULL crashes the kernel.

Post by ffexl »

I just tested switching NULL for (void *)0. Same error
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Octocontrabass
Member
Member
Posts: 5868
Joined: Mon Mar 25, 2013 7:01 pm

Re: Assigning a pointer NULL crashes the kernel.

Post by Octocontrabass »

ffexl wrote: ↑Mon Jun 23, 2025 8:08 pm

Code: Select all

check_exception old: 0xffffffff new 0x6
     0: v=06 e=0000 i=0 cpl=0 IP=0028:ffffffff800036b5
It's an undefined opcode exception. Can you disassemble the instruction at 0xffffffff800036b5?
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ffexl
Posts: 7
Joined: Wed Apr 23, 2025 11:16 pm

Re: Assigning a pointer NULL crashes the kernel.

Post by ffexl »

Code: Select all

(lldb) disassemble --start-address 0xffffffff800036b5
BaseOS.bin`list_init:
->  0xffffffff800036b5 <+5>:  xorps  %xmm0, %xmm0
    0xffffffff800036b8 <+8>:  movups %xmm0, (%rdi)
    0xffffffff800036bb <+11>: movq   $0x0, 0x10(%rdi)
    0xffffffff800036c3 <+19>: retq   
    0xffffffff800036c4 <+20>: pushq  %rbp
    0xffffffff800036c5 <+21>: movq   %rsp, %rbp
    0xffffffff800036c8 <+24>: movq   $-0x7fff8fb5, %rdi        ; imm = 0x8000704B
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Octocontrabass
Member
Member
Posts: 5868
Joined: Mon Mar 25, 2013 7:01 pm

Re: Assigning a pointer NULL crashes the kernel.

Post by Octocontrabass »

You can't use SSE instructions unless you've enabled SSE support.

Typically you don't want SSE instructions in your kernel, even if you do enable SSE support, since that's more registers you need to save and restore every time you switch between kernel and user mode. Compile with "-mgeneral-regs-only" to tell Clang you don't want it to use SSE instructions (or any other instructions that require saving additional registers).
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ffexl
Posts: 7
Joined: Wed Apr 23, 2025 11:16 pm

Re: Assigning a pointer NULL crashes the kernel.

Post by ffexl »

That worked! Thank you! I knew it wasn't a code problem. As usual, the most frustrating bugs come from the build system. Do you have any more useful compiler or linker flags that would save me trouble in the future?

Right now I just have my C_FLAGS set as "--target=x86_64-pc-none-elf -Wall -Wextra -ffreestanding -mcmodel=kernel -mno-red-zone -fno-stack-protector -fno-stack-check -fno-pie -Og -g -gdwarf-4 -mgeneral-regs-only"

And my linker set as "-v -fuse-ld=lld -Wl,-T,${CMAKE_SOURCE_DIR}/${LINKER} -fno-pie -ffreestanding -nostdlib -Wl,-z,max-page-size=0x1000 -Wl,-z,notext -static"
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nullplan
Member
Member
Posts: 1907
Joined: Wed Aug 30, 2017 8:24 am

Re: Assigning a pointer NULL crashes the kernel.

Post by nullplan »

I would actually get rid of the "-Wl,-z,notext" if I were you. According to the manpage, that suppresses an error if relocations are generated against the text segment. But you are creating a static executable, there shouldn't be any relocations at all, against .text or otherwise. Beyond that, this looks fairly complete, and contains pretty much the flags I'd use.
Carpe diem!
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