3
For variadic macros, stick with this C99-like syntax:
5
#define DPRINTF(fmt, ...) \
6
do { printf("IRQ: " fmt, ## __VA_ARGS__); } while (0)
10
It should be common sense to use the right type, but we have collected
11
a few useful guidelines here.
15
If you're using "int" or "long", odds are good that there's a better type.
16
If a variable is counting something, it should be declared with an
19
If it's host memory-size related, size_t should be a good choice (use
20
ssize_t only if required). Guest RAM memory offsets must use ram_addr_t,
21
but only for RAM, it may not cover whole guest address space.
23
If it's file-size related, use off_t.
24
If it's file-offset related (i.e., signed), use off_t.
25
If it's just counting small numbers use "unsigned int";
26
(on all but oddball embedded systems, you can assume that that
27
type is at least four bytes wide).
29
In the event that you require a specific width, use a standard type
30
like int32_t, uint32_t, uint64_t, etc. The specific types are
31
mandatory for VMState fields.
33
Don't use Linux kernel internal types like u32, __u32 or __le32.
35
Use target_phys_addr_t for guest physical addresses except pcibus_t
36
for PCI addresses. In addition, ram_addr_t is a QEMU internal address
37
space that maps guest RAM physical addresses into an intermediate
38
address space that can map to host virtual address spaces. Generally
39
speaking, the size of guest memory can always fit into ram_addr_t but
40
it would not be correct to store an actual guest physical address in a
43
Use target_ulong (or abi_ulong) for CPU virtual addresses, however
44
devices should not need to use target_ulong.
46
Of course, take all of the above with a grain of salt. If you're about
47
to use some system interface that requires a type like size_t, pid_t or
48
off_t, use matching types for any corresponding variables.
50
Also, if you try to use e.g., "unsigned int" as a type, and that
51
conflicts with the signedness of a related variable, sometimes
52
it's best just to use the *wrong* type, if "pulling the thread"
53
and fixing all related variables would be too invasive.
55
Finally, while using descriptive types is important, be careful not to
56
go overboard. If whatever you're doing causes warnings, or requires
57
casts, then reconsider or ask for help.
61
Ensure that all of your pointers are "const-correct".
62
Unless a pointer is used to modify the pointed-to storage,
63
give it the "const" attribute. That way, the reader knows
64
up-front that this is a read-only pointer. Perhaps more
65
importantly, if we're diligent about this, when you see a non-const
66
pointer, you're guaranteed that it is used to modify the storage
67
it points to, or it is aliased to another pointer that is.
70
Typedefs are used to eliminate the redundant 'struct' keyword.
72
2.4. Reserved namespaces in C and POSIX
73
Underscore capital, double underscore, and underscore 't' suffixes should be
76
3. Low level memory management
78
Use of the malloc/free/realloc/calloc/valloc/memalign/posix_memalign
79
APIs is not allowed in the QEMU codebase. Instead of these routines,
80
use the replacement qemu_malloc/qemu_mallocz/qemu_realloc/qemu_free or
81
qemu_vmalloc/qemu_memalign/qemu_vfree APIs.
83
Please note that NULL check for the qemu_malloc result is redundant and
84
that qemu_malloc() call with zero size is not allowed.
86
Memory allocated by qemu_vmalloc or qemu_memalign must be freed with
87
qemu_vfree, since breaking this will cause problems on Win32 and user
90
4. String manipulation
92
Do not use the strncpy function. According to the man page, it does
93
*not* guarantee a NULL-terminated buffer, which makes it extremely dangerous
94
to use. Instead, use functionally equivalent function:
95
void pstrcpy(char *buf, int buf_size, const char *str)
97
Don't use strcat because it can't check for buffer overflows, but:
98
char *pstrcat(char *buf, int buf_size, const char *s)
100
The same limitation exists with sprintf and vsprintf, so use snprintf and
103
QEMU provides other useful string functions:
104
int strstart(const char *str, const char *val, const char **ptr)
105
int stristart(const char *str, const char *val, const char **ptr)
106
int qemu_strnlen(const char *s, int max_len)
108
There are also replacement character processing macros for isxyz and toxyz,
109
so instead of e.g. isalnum you should use qemu_isalnum.
111
Because of the memory management rules, you must use qemu_strdup/qemu_strndup
112
instead of plain strdup/strndup.
114
5. Printf-style functions
116
Whenever you add a new printf-style function, i.e., one with a format
117
string argument and following "..." in its prototype, be sure to use
118
gcc's printf attribute directive in the prototype.
120
This makes it so gcc's -Wformat and -Wformat-security options can do
121
their jobs and cross-check format strings with the number and types
added
removed
HACKING
