155 lines
4.6 KiB
HTML
155 lines
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<h1>malloc(3)</h1>
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<pre><code><strong>NAME</strong>
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malloc, mfree, realloc - userspace heap allocation
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<strong>SYNOPSIS</strong>
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<strong> void* montauk::malloc(uint64_t size);</strong>
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<strong> void montauk::mfree(void* ptr);</strong>
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<strong> void* montauk::realloc(void* ptr, uint64_t size);</strong>
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<strong>DESCRIPTION</strong>
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The userspace heap provides dynamic memory allocation on top of
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the kernel's page-mapping syscall (SYS_ALLOC). Include the
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header <montauk/heap.h> to use these functions.
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<strong>malloc</strong>
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Allocates 'size' bytes from the free list. Returns a 16-byte
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aligned pointer, or nullptr on failure. When the free list is
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empty, it requests more pages from the kernel via SYS_ALLOC
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(minimum 16 KiB growth, initial seed of 64 KiB).
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char* buf = (char*)montauk::malloc(1024);
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<strong>mfree</strong>
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Returns the block to the userspace free list. No syscall is
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made -- the memory stays mapped and is immediately reusable.
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Passing nullptr is a safe no-op.
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montauk::mfree(buf);
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<strong>realloc</strong>
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Resizes the allocation to 'size' bytes. Allocates a new block,
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copies the smaller of old/new sizes, and frees the old block.
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If ptr is nullptr, behaves like malloc.
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buf = (char*)montauk::realloc(buf, 2048);
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<strong>IMPLEMENTATION</strong>
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The allocator uses a linked free-list with first-fit search.
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Blocks larger than needed are split. The allocation header is
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16 bytes (magic + size). All allocations are 16-byte aligned.
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The heap grows by requesting pages from the kernel via
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SYS_ALLOC. These pages are never returned to the kernel (since
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SYS_FREE is currently a no-op), but mfree makes them available
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for future malloc calls within the process.
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<strong>LOW-LEVEL PAGE API</strong>
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For large allocations or when direct page control is needed:
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void* montauk::alloc(uint64_t size); // SYS_ALLOC
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void montauk::free(void* ptr); // SYS_FREE (no-op)
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alloc() maps zeroed pages starting at 0x40000000 and growing
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upward. Size is rounded up to 4 KiB page boundaries.
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<strong>SEE ALSO</strong>
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syscalls(2), file(2)</code></pre>
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