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65 lines
2.3 KiB
C
65 lines
2.3 KiB
C
#include "../kernel.h"
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#include "ktypes.h"
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#include "malloc.h"
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#include "ecall.h"
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#include "io.h"
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// information about the systems memory layout is stored here
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static struct malloc_info global_malloc_info = { 0 };
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// this pointer points to the end of unused memory
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static void* allocate_memory_end;
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// this stack holds currently unused program stacks
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// it is a stack in the sense that you can push and pop variables
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static struct voidptr_stack unused_stacks;
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void stash_stack(void* stack_top)
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{
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if (voidptr_stack_push(&unused_stacks, stack_top) == 0) {
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// if this happens, we know we messed up and created more stacks than we
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// could ever have processes running simultaneously!
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// we probably have an erro in retrieving stashed stacks?
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dbgln("cannot stash stack, no space left! This should never ever happen!", 65);
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}
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}
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// this function is called by the kernels init() function after it parsed the
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// list of loaded binaries and calculated the available memory for general allocation
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void malloc_init(struct malloc_info* given_info)
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{
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// save the passed info
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global_malloc_info = *given_info;
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allocate_memory_end = given_info->allocate_memory_end;
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allocate_memory_end = (void*) (((int) allocate_memory_end) - PROCESS_COUNT);
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voidptr_stack_new(&unused_stacks, (void**) allocate_memory_end, PROCESS_COUNT);
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}
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// allocate stack and return a pointer to the *end* of the allocated region
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// this doesn't reuse stack from functions which exited
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optional_voidptr malloc_stack()
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{
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// try to reuse a stack top
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void* stack_top = voidptr_stack_pop(&unused_stacks);
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if (stack_top != NULL) {
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return (optional_voidptr) { .value = stack_top };
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}
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// otherwise allocate a new stack at the end of available memory
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void* new_alloc_end = (void*) (((int) allocate_memory_end) - USER_STACK_SIZE);
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// check if we ran out of space
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if (new_alloc_end < global_malloc_info.allocate_memory_start)
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return (optional_voidptr) { .error = ENOMEM };
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stack_top = allocate_memory_end;
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allocate_memory_end = new_alloc_end;
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return (optional_voidptr) { .value = stack_top };
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}
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// a stack is not returned to the general memory pool (since EMBARK has no such
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// pool) but rather just added to the pool of free process stacks.
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void free_stack(void* stack_top)
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{
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stash_stack(stack_top);
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}
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