44 lines
2.2 KiB
Org Mode
44 lines
2.2 KiB
Org Mode
The provided pseudocode outlines a modified implementation
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of jemalloc’s memory mapping routines, adapted to work with
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a custom malloc(sz) allocator. Instead of relying on traditional
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operating system mechanisms like mmap, the memory allocation is
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handled using MALLOC(size), which refers to a simplified allocator
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defined earlier. This custom allocator manages a preallocated
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memory region, aligns the requested size, decrements a memory
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counter, and returns a pointer with enforced bounds for memory
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safety. This approach is especially suited for constrained or
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security-focused environments such as CHERI, where strict
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control over memory access and deterministic allocation
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behavior is essential.
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The os_pages_map function simulates jemalloc’s low-level page
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mapping routine. It first checks if a specific address is
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requested—a case relevant to CheriABI where such behavior
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is disallowed—and returns NULL if so. If memory overcommitment
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is allowed, it forces the commit flag to true. It then allocates
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memory using the custom MALLOC(size) function and validates
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whether the returned pointer matches the requested address
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(if one was provided). If there’s a mismatch, it unmaps the
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memory and returns NULL; otherwise, it returns the allocated
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pointer.
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The pages_map function is a simplified variant that ignores
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alignment and address constraints. It directly allocates the
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requested memory size using the internal allocator and returns
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the result. This is appropriate in scenarios where alignment is
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either managed elsewhere or not critical.
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The pages_commit_impl function emulates memory commitment, a
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feature in systems that support lazy memory allocation. It
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reallocates memory using MALLOC(size) and checks whether
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the returned pointer matches the expected address. If not,
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it unmaps the memory and signals failure by returning true;
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otherwise, it indicates success by returning false.
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Collectively, these routines demonstrate how jemalloc can be
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adapted to operate atop a custom memory allocator instead of
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relying on the OS. This enables jemalloc to function in
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specialized environments that require stricter memory controls,
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such as embedded systems or capability-based architectures,
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while still maintaining its structure and allocation policies.
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