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Scanning for useful mem for heap

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This commit is contained in:
Thomas Oltmann 2025-07-05 19:30:14 +02:00
parent 77d791f177
commit 50d9e63041
1 changed files with 53 additions and 0 deletions
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53
lboot.S
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@ -29,6 +29,10 @@ _start: cli
call print
call getmap
mov $msg_mkheap, %si
call print
call makeheap
mov $msg_paging, %si
call print
call paging
@ -130,6 +134,51 @@ _pgnext: mov %ecx, %eax
ret
// makeheap: find a memory range suitable for heap usage
makeheap: mov $memmap-24, %si
_mhnext: add $24, %si
cmp memmap_end, %si
jae _mhdone
cmpl $1, 16(%si)
jne _mhnext
cmpl $0, 4(%si)
ja _mhnext
mov 0(%si), %ebx
mov 8(%si), %ecx
// find end of range, clip to 4Gb
add %ebx, %ecx
jnc 1f
mov $0xFFFFFFFF, %ecx
// handle wraparound if length > 4Gb
1: cmpl $0, 12(%si)
je 1f
mov $0xFFFFFFFF, %ecx
// adjust base to above 1Mb, above the bootloader
1: cmp $0x10000, %ebx
jae 1f
mov $0x10000, %ebx
// align to 4Kb boundaries
1: add $0xFFF, %ebx
and $0xFFFFF000, %ebx
and $0xFFFFF000, %ecx
sub %ebx, %ecx
cmp heap_size, %ecx
jbe _mhnext
mov %ebx, heap_start
mov %ecx, heap_size
jmp _mhnext
_mhdone: ret
// alloc: take ECX bytes from usable space in memmap
// No realignment is performed, so only alloc aligned sizes.
alloc: mov $memmap-24, %si
@ -203,10 +252,14 @@ msg_start: .asciz "Netboot via fernlader v1 ...\r\n"
msg_a20: .asciz " * Enabling A20\r\n"
msg_unreal: .asciz " * Unreal Mode\r\n"
msg_getmap: .asciz " * Memory Map\r\n"
msg_mkheap: .asciz " * Making Space\r\n"
msg_paging: .asciz " * Paging\r\n"
msg_fin: .asciz "Finished.\r\n"
msg_aerr: .asciz "panic: Unable to allocate memory.\r\n"
heap_start: .long 0
heap_size: .long 0
// Long mode initial page tables
pd_ptr: .long 0
pdp_ptr: .long 0