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Fix miscellaneous kernel bugs found when upgrading Limine #200

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Fix miscellaneous kernel bugs found when upgrading Limine #200

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e1daa29
Fix SYS_RAM_REBOOT reading the boot stack through a RIP-relative address
Mintsuki Sep 14, 2026
4358f08
Only add usable E820 memory to the code heap
Mintsuki Sep 13, 2026
ddbc7ae
Remove E801 from the kernel
Mintsuki Sep 13, 2026
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Binary file modified build/AUTO.ISO
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21 changes: 1 addition & 20 deletions src/Kernel/KStart16.ZC
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Expand Up @@ -28,7 +28,6 @@ SYS_RUN_LEVEL:: DU32 0;
#assert SYS_COMPILE_TIME + sizeof(CDate) + sizeof(CZXE) < DVD_BLK_SIZE

MEM_BOOT_BASE:: DU32 0; //Offset from start used by reboot
MEM_E801:: DU16 0, 0;
MEM_E820:: DU8 MEM_E820_ENTRIES_NUM * sizeof(CMemE820) DUP (0);
MEM_PHYSICAL_SPACE:: DU64 0;
SYS_GDT_PTR:: DU16 sizeof(CGDT) - 1;
Expand Down Expand Up @@ -244,19 +243,6 @@ GET_IP: POP BX
BTS U32 [SYS_RUN_LEVEL], RLf_VESA
@@35:

//Get E801 memory map.
//Output: AX = Memory between 1MiB and 16MiB in KiB (max 0x3C00 == 15 MiB)
// BX = Memory after 16MiB until first memory hole in 64KiB blocks.
XOR CX, CX
XOR DX, DX
MOV AX, 0xE801
INT 0x15
JCXZ @@40 //if CX and DX are zero, use AX and BX instead.
MOV AX, CX
MOV BX, DX
@@40: MOV U16 [MEM_E801], AX
MOV U16 [MEM_E801+2], BX

//Get E820 memory map.
MOV CX, MEM_E820_ENTRIES_NUM - 1 //Leave one to terminate
XOR EBX, EBX
Expand All @@ -279,14 +265,9 @@ GET_IP: POP BX
SUB SP, 2
@@50: ADD SP, 2 //if called failed we want to nullify the PUSHed CX value.

//Find how much space to map, start with E801 limit.
//Find max of E820 to set mapped space.
XOR EAX, EAX
MOV AX, [MEM_E801+2]
SHL EAX, 16
ADD EAX, SYS_16MEG_AREA_LIMIT
XOR EDX, EDX

//Find max of E820 to set mapped space.
MOV SI, MEM_E820
@@55: MOV CL, CMemE820.type[SI]
TEST CL, CL
Expand Down
3 changes: 2 additions & 1 deletion src/Kernel/KStart64.ZC
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Expand Up @@ -82,8 +82,9 @@ USE64

//************************************
SYS_RAM_REBOOT:: //This gets copied high. $LK,"SYS_RAM_REBOOT",A="FF:::/System/Boot/BootRAM.ZC,SYS_RAM_REBOOT:2"$
MOV EAX, I32 SYS_BOOT_STACK //Not RIP-relative, as this runs from the copy.
PUSH U32 CGDT.ds //stack seg
PUSH U32 [SYS_BOOT_STACK]//stack
PUSH U32 [RAX] //stack
PUSH U32 0 //flags
PUSH U32 CGDT.cs32
LEA RAX, [@@10]
Expand Down
1 change: 0 additions & 1 deletion src/Kernel/KernelA.HH
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Expand Up @@ -558,7 +558,6 @@ class CKernel

U0 start;
U32 boot_base;
U16 mem_E801[2];
CMemE820 mem_E820[MEM_E820_ENTRIES_NUM];
U64 mem_physical_space;
CSysLimitBase sys_gdt_ptr;
Expand Down
15 changes: 14 additions & 1 deletion src/Kernel/Memory/BlkPool.ZC
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Expand Up @@ -44,7 +44,20 @@ U0 BlkPoolsInit()
code_heap_limit = 0x80000000;

i = code_heap_limit - SYS_16MEG_AREA_LIMIT; //See $LK,"RLf_16MEG_SYS_CODE_BP",A="FF:::/Kernel/Memory/PageTables.ZC,RLf_16MEG_SYS_CODE_BP"$
BlkPoolAdd(sys_code_bp, SYS_16MEG_AREA_LIMIT, i >> MEM_PAG_BITS);
while (m20->type)
{//The memory below the limit can have holes, so only add the usable E820 ranges.
if (m20->type == MEM_E820t_USABLE)
{
lo = m20->base;
hi = m20->base + m20->len;
lo = CeilI64(MaxI64(lo, SYS_16MEG_AREA_LIMIT), MEM_PAG_SIZE);
hi = FloorI64(MinI64(hi, code_heap_limit), MEM_PAG_SIZE);
if (lo < hi)
BlkPoolAdd(sys_code_bp, lo, (hi - lo) >> MEM_PAG_BITS);
}
m20++;
}
m20 = MEM_E820;
mem_heap_limit = i + SYS_16MEG_AREA_LIMIT - 1;

if (code_heap_limit<total)
Expand Down
10 changes: 3 additions & 7 deletions src/Kernel/Memory/MemPhysical.ZC
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Expand Up @@ -171,14 +171,10 @@ U0 UncachedAliasAlloc() //Make uncached alias for 4 lowest Gig.
}

I64 MemBIOSTotal()
{//Returns max of either E801 or E820 mem map.
I64 total01 = 0x100000, total20 = 0;
U16 *mem01 = MEM_E801;
{//Returns total usable memory in the E820 mem map.
I64 total20 = 0;
CMemE820 *mem20 = MEM_E820;

total01 += mem01[0] * 1024; //First U16 is mem between 1MiB and 16 MiB in KiB.
total01 += mem01[1] * 64 * 1024;//Second U16 is mem above 16MiB (until it encounters a hole) in 64KiB blocks.

if (mem20->type)
{
while (mem20->type)
Expand All @@ -188,7 +184,7 @@ I64 MemBIOSTotal()
mem20++;
}
}
return MaxI64(total01, total20);
return total20;
}

I64 Scale2Mem(I64 min, I64 max, I64 limit=2*1024*1024*1024)
Expand Down
58 changes: 42 additions & 16 deletions src/Kernel/Memory/PageTables.ZC
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Expand Up @@ -154,24 +154,52 @@ SYS_INIT_PAGE_TABLES::
RET

SYS_INIT_16MEG_SYS_CODE_BP::
// Init sys_code_bp to BIOS E801 lowest 16Meg value.
// Init sys_code_bp to the BIOS E820 usable memory below 16Meg.
// $LK,"BlkPoolsInit",A="MN:BlkPoolsInit"$() adds the rest.
MOV U32 [SYS_CODE_BP], SYS_FIXED_AREA + CSysFixedArea.sys_code_bp
MOV U32 [SYS_CODE_BP + 4], 0

MOV U32 [SYS_DATA_BP], 0
MOV U32 [SYS_DATA_BP + 4], 0

XOR EAX, EAX
MOV AX, U16 [MEM_E801] //1 Kb blocks between 1M and 16M
SHL EAX, 10
ADD EAX, 0x100000
MOV ESI, MEM_E820
JMP @@10
@@05: ADD ESI, sizeof(CMemE820)
@@10: MOV AL, U8 CMemE820.type[ESI]
TEST AL, AL
JNZ @@15
BTS U32 [SYS_RUN_LEVEL], RLf_16MEG_SYS_CODE_BP
RET

@@15: CMP AL, MEM_E820t_USABLE
JNE @@05
CMP U32 CMemE820.base + 4 [ESI], 0
JNE @@05
MOV EDI, U32 CMemE820.base[ESI]
CMP EDI, SYS_16MEG_AREA_LIMIT
JAE @@05

//Clip the range to between the page tables and 16Meg, whole pages only.
MOV EAX, EDI
XOR EDX, EDX
ADD EAX, U32 CMemE820.len[ESI]
ADC EDX, U32 CMemE820.len + 4 [ESI]
JNZ @@20
CMP EAX, SYS_16MEG_AREA_LIMIT
JBE @@25
@@20: MOV EAX, SYS_16MEG_AREA_LIMIT
@@25: CMP EDI, U32 [MEM_HEAP_BASE]
JAE @@30
MOV EDI, U32 [MEM_HEAP_BASE]
@@30: ADD EDI, MEM_PAG_SIZE - 1
AND EDI, ~(MEM_PAG_SIZE - 1)
AND EAX, ~(MEM_PAG_SIZE - 1)
SUB EAX, EDI
JBE @@05

//EDI=BASE EAX=SIZE
TEST U8 [SYS_MEM_INIT_FLAG], 1
JZ @@05
JZ @@35
PUSH EAX
PUSH EDI
MOV ECX, EAX
Expand All @@ -180,20 +208,18 @@ SYS_INIT_16MEG_SYS_CODE_BP::
POP EDI
POP EAX

@@05: SHR EAX, MEM_PAG_BITS
MOV ESI, SYS_FIXED_AREA + CSysFixedArea.sys_code_bp
MOV EBX, U32 CBlkPool.mem_free_list[ESI]
MOV U32 CMemBlk.next [EDI], EBX
@@35: SHR EAX, MEM_PAG_BITS
MOV EBX, SYS_FIXED_AREA + CSysFixedArea.sys_code_bp
MOV ECX, U32 CBlkPool.mem_free_list[EBX]
MOV U32 CMemBlk.next [EDI], ECX
MOV U32 CMemBlk.next + 4 [EDI], 0
MOV U32 CBlkPool.mem_free_list [ESI], EDI
MOV U32 CBlkPool.mem_free_list + 4 [ESI], 0
MOV U32 CBlkPool.mem_free_list [EBX], EDI
MOV U32 CBlkPool.mem_free_list + 4 [EBX], 0
MOV U32 CMemBlk.mb_signature[EDI], MBS_UNUSED_SIGNATURE_VAL
MOV U32 CMemBlk.pags[EDI], EAX
SHL EAX, MEM_PAG_BITS
ADD U32 CBlkPool.alloced_u8s[ESI], EAX

BTS U32 [SYS_RUN_LEVEL], RLf_16MEG_SYS_CODE_BP
RET
ADD U32 CBlkPool.alloced_u8s[EBX], EAX
JMP I32 @@05
}

I64 *MemPageTable(U8 *a)
Expand Down
9 changes: 0 additions & 9 deletions src/System/DevInfo.ZC
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Expand Up @@ -110,7 +110,6 @@ public U0 PCIRep()
#help_index "Info;Memory/Info"
public U0 MemBIOSRep()
{//Report the memory ranges reported by the BIOS at boot.
U16 *m01 = MEM_E801;
CMemE820 *m20 = MEM_E820;
CMemRange *tmpmr;

Expand Down Expand Up @@ -143,14 +142,6 @@ public U0 MemBIOSRep()
}
LBtr(&sys_semas[SEMA_DEV_MEM], 0);

if (!IsRaw)
"\n$$PURPLE$$BIOS Memory Report 15:E801$$FG$$\n";
else
"\nBIOS Memory Report 15:E801\n";

"0000000000000000-%016X\n", 0x100000 + m01[0] * 1024 - 1;
"0000000001000000-%016X\n", SYS_16MEG_AREA_LIMIT + m01[1] * 64 * 1024 - 1;

if (m20->type)
{
if (!IsRaw)
Expand Down
33 changes: 0 additions & 33 deletions zealbooter/src/zealbooter.c
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Expand Up @@ -120,7 +120,6 @@ struct CKernel {
struct CDate compile_time;
// U0 start
uint32_t boot_base;
uint16_t mem_E801[2];
struct CMemE820 mem_E820[MEM_E820_ENTRIES_NUM];
uint64_t mem_physical_space;
struct CSysLimitBase sys_gdt_ptr;
Expand Down Expand Up @@ -151,34 +150,6 @@ struct CKernel {

extern symbol trampoline, trampoline_end;

struct E801 {
size_t lowermem;
size_t uppermem;
};

static struct E801 get_E801(void) {
struct E801 E801 = {0};

for (size_t i = 0; i < memmap_request.response->entry_count; i++) {
struct limine_memmap_entry *entry = memmap_request.response->entries[i];

if (entry->type == LIMINE_MEMMAP_USABLE) {
if (entry->base == 0x100000) {
if (entry->length > 0xf00000) {
E801.lowermem = 0x3c00;
} else {
E801.lowermem = entry->length / 1024;
}
}
if (entry->base <= 0x1000000 && entry->base + entry->length > 0x1000000) {
E801.uppermem = ((entry->length - (0x1000000 - entry->base)) / 1024) / 64;
}
}
}

return E801;
}

void kmain(void) {
printf("ZealBooter prekernel\n");
printf("____________________\n\n");
Expand Down Expand Up @@ -277,10 +248,6 @@ void kmain(void) {

kernel->sys_pci_buses = 256;

struct E801 E801 = get_E801();
kernel->mem_E801[0] = E801.lowermem;
kernel->mem_E801[1] = E801.uppermem;

kernel->mem_physical_space = 0;

printf("memory map:\n");
Expand Down
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