1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
|
/*
* Copyright (c) 2017 Richard Braun.
* Copyright (c) 2017 Jerko Lenstra.
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*
*
* Kernel dynamic memory allocator.
*
* Here, the word "dynamic" is used in opposition to "static", which denotes
* memory allocated at compile time by the linker.
*/
#ifndef _MEM_H
#define _MEM_H
#include <stddef.h>
/*
* Initialize the mem module.
*/
void mem_setup(void);
/*
* Allocate memory.
*
* This function conforms to the specification of the standard malloc()
* function, i.e. :
* - The size argument is the allocation request size, in bytes.
* - An allocation size of 0 is permitted.
* - The content of the allocated block is uninitialized.
* - The returned value is the address of the allocated block of memory.
* - The address of the allocated block is aligned to the maximum built-in
* type size. Since this code targets the 32-bits i386 architecture, the
* largest built-in type is unsigned int, resulting in addresses aligned
* to 4 bytes boundaries. Here, "built-in" means natively supported by
* the processor. The document that defines the size of built-in types
* is the ABI (Application Binary Interface) specification, in this case
* System V Intel386 ABI [1] (see the GCC -mabi option for x86). The ABI
* normally uses one of the most common data models [2] for C types, in
* this case ILP32 (for int/long/pointers 32-bits).
*
* This last detail is important because C specifies the alignment of both
* built-in and aggregate types. In particular, the alignment of structure
* members must match the alignment of their respective types
* (ISO/IEC 9899:1999, 6.7.2.1 "Structure and union specifiers", 12 "Each
* non-bit-field member of a structure or union object is aligned in an
* implementation-defined manner appropriate to its type". A compiler may
* safely assume that structure member accesses are correctly aligned and
* generate instructions assuming this alignment.
*
* On x86, this doesn't matter too much, because unaligned accesses have
* always been supported, although they are less performant, since the
* processor potentially has more work to do. For example, if an unaligned
* variable crosses a cache line boundary, the processor may have to load
* two cache lines instead of one.
*
* On other architectures, unaligned accesses may simply not be supported,
* and generate exceptions.
*
* [1] http://www.sco.com/developers/devspecs/abi386-4.pdf
* [2] http://www.unix.org/version2/whatsnew/lp64_wp.html
*/
void * mem_alloc(size_t size);
/*
* Free memory.
*
* This function conforms to the specification of the standard free()
* function, i.e. :
* - It may safely be called with a NULL argument.
* - Otherwise, it may only be passed memory addresses returned by mem_alloc().
*/
void mem_free(void *ptr);
#endif /* _MEM_H */
|