78 lines
2.0 KiB
C
78 lines
2.0 KiB
C
/**********************************
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* bump_alloc.c
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* Jeremy.Singer@glasgow.ac.uk
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*
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* This is a simple bump-pointer allocator.
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* It mmaps a large buffer of SIZE bytes,
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* then allocates this space in word-sized
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* chunks to client code (in main fn).
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*
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* Initial simple memory allocator test.
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* Explore capability narrowing operations
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* and intrinsics for bound reporting.
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*/
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#include <cheriintrin.h>
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#include <errno.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/mman.h>
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#include "bump_alloc.h"
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int count = 0; /* number of bytes allocated so far*/
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int max = 0; /* upper limit for count */
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char *buffer = NULL; /* the allocation buffer */
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void init_alloc(int size_in_bytes)
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{
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/* request memory for our allocation buffer
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* NB mmap min bounds for capability is 1 page (4K)
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*/
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char *res = mmap(NULL, size_in_bytes, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
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if (res == MAP_FAILED)
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{
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perror("error in initial mem allocation");
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exit(-1);
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}
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buffer = res;
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max = size_in_bytes;
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return;
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}
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/*
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* allocate len bytes with bump pointer allocator
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* this is our simplistic `malloc` function
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*/
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void *malloc(size_t len)
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{
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char *chunk = buffer + count;
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size_t rounded_len; /* for CHERI alignment */
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size_t new_count; /* for buffer overflow check */
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/* ensure we can represent the capability accurately,
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* see p30 of CHERI C/C++ Prog Guide (June 2020)
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* www.cl.cam.ac.uk/techreports/UCAM-CL-TR-947
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*/
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chunk = __builtin_align_up(chunk, ~cheri_representable_alignment_mask(len) + 1);
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rounded_len = cheri_representable_length(len);
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new_count = (chunk + rounded_len) - buffer;
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if (new_count > max)
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{
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/* out of bounds - don't allocate anything */
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chunk = 0;
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}
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else
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{
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/* restrict capability range before returning ptr */
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chunk = cheri_bounds_set_exact(chunk, rounded_len);
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/* update bytes allocated count */
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count = new_count;
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}
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return chunk;
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} |