9b9e3ec1b4
Reword the section on strncpy: its NUL-filling is important in some cases. Mention that pstrcpy's signature is different. Signed-off-by: Jim Meyering <meyering@redhat.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
126 lines
5.0 KiB
Plaintext
126 lines
5.0 KiB
Plaintext
1. Preprocessor
|
|
|
|
For variadic macros, stick with this C99-like syntax:
|
|
|
|
#define DPRINTF(fmt, ...) \
|
|
do { printf("IRQ: " fmt, ## __VA_ARGS__); } while (0)
|
|
|
|
2. C types
|
|
|
|
It should be common sense to use the right type, but we have collected
|
|
a few useful guidelines here.
|
|
|
|
2.1. Scalars
|
|
|
|
If you're using "int" or "long", odds are good that there's a better type.
|
|
If a variable is counting something, it should be declared with an
|
|
unsigned type.
|
|
|
|
If it's host memory-size related, size_t should be a good choice (use
|
|
ssize_t only if required). Guest RAM memory offsets must use ram_addr_t,
|
|
but only for RAM, it may not cover whole guest address space.
|
|
|
|
If it's file-size related, use off_t.
|
|
If it's file-offset related (i.e., signed), use off_t.
|
|
If it's just counting small numbers use "unsigned int";
|
|
(on all but oddball embedded systems, you can assume that that
|
|
type is at least four bytes wide).
|
|
|
|
In the event that you require a specific width, use a standard type
|
|
like int32_t, uint32_t, uint64_t, etc. The specific types are
|
|
mandatory for VMState fields.
|
|
|
|
Don't use Linux kernel internal types like u32, __u32 or __le32.
|
|
|
|
Use target_phys_addr_t for guest physical addresses except pcibus_t
|
|
for PCI addresses. In addition, ram_addr_t is a QEMU internal address
|
|
space that maps guest RAM physical addresses into an intermediate
|
|
address space that can map to host virtual address spaces. Generally
|
|
speaking, the size of guest memory can always fit into ram_addr_t but
|
|
it would not be correct to store an actual guest physical address in a
|
|
ram_addr_t.
|
|
|
|
Use target_ulong (or abi_ulong) for CPU virtual addresses, however
|
|
devices should not need to use target_ulong.
|
|
|
|
Of course, take all of the above with a grain of salt. If you're about
|
|
to use some system interface that requires a type like size_t, pid_t or
|
|
off_t, use matching types for any corresponding variables.
|
|
|
|
Also, if you try to use e.g., "unsigned int" as a type, and that
|
|
conflicts with the signedness of a related variable, sometimes
|
|
it's best just to use the *wrong* type, if "pulling the thread"
|
|
and fixing all related variables would be too invasive.
|
|
|
|
Finally, while using descriptive types is important, be careful not to
|
|
go overboard. If whatever you're doing causes warnings, or requires
|
|
casts, then reconsider or ask for help.
|
|
|
|
2.2. Pointers
|
|
|
|
Ensure that all of your pointers are "const-correct".
|
|
Unless a pointer is used to modify the pointed-to storage,
|
|
give it the "const" attribute. That way, the reader knows
|
|
up-front that this is a read-only pointer. Perhaps more
|
|
importantly, if we're diligent about this, when you see a non-const
|
|
pointer, you're guaranteed that it is used to modify the storage
|
|
it points to, or it is aliased to another pointer that is.
|
|
|
|
2.3. Typedefs
|
|
Typedefs are used to eliminate the redundant 'struct' keyword.
|
|
|
|
2.4. Reserved namespaces in C and POSIX
|
|
Underscore capital, double underscore, and underscore 't' suffixes should be
|
|
avoided.
|
|
|
|
3. Low level memory management
|
|
|
|
Use of the malloc/free/realloc/calloc/valloc/memalign/posix_memalign
|
|
APIs is not allowed in the QEMU codebase. Instead of these routines,
|
|
use the GLib memory allocation routines g_malloc/g_malloc0/g_new/
|
|
g_new0/g_realloc/g_free or QEMU's qemu_vmalloc/qemu_memalign/qemu_vfree
|
|
APIs.
|
|
|
|
Please note that g_malloc will exit on allocation failure, so there
|
|
is no need to test for failure (as you would have to with malloc).
|
|
Calling g_malloc with a zero size is valid and will return NULL.
|
|
|
|
Memory allocated by qemu_vmalloc or qemu_memalign must be freed with
|
|
qemu_vfree, since breaking this will cause problems on Win32 and user
|
|
emulators.
|
|
|
|
4. String manipulation
|
|
|
|
Do not use the strncpy function. As mentioned in the man page, it does *not*
|
|
guarantee a NULL-terminated buffer, which makes it extremely dangerous to use.
|
|
It also zeros trailing destination bytes out to the specified length. Instead,
|
|
use this similar function when possible, but note its different signature:
|
|
void pstrcpy(char *dest, int dest_buf_size, const char *src)
|
|
|
|
Don't use strcat because it can't check for buffer overflows, but:
|
|
char *pstrcat(char *buf, int buf_size, const char *s)
|
|
|
|
The same limitation exists with sprintf and vsprintf, so use snprintf and
|
|
vsnprintf.
|
|
|
|
QEMU provides other useful string functions:
|
|
int strstart(const char *str, const char *val, const char **ptr)
|
|
int stristart(const char *str, const char *val, const char **ptr)
|
|
int qemu_strnlen(const char *s, int max_len)
|
|
|
|
There are also replacement character processing macros for isxyz and toxyz,
|
|
so instead of e.g. isalnum you should use qemu_isalnum.
|
|
|
|
Because of the memory management rules, you must use g_strdup/g_strndup
|
|
instead of plain strdup/strndup.
|
|
|
|
5. Printf-style functions
|
|
|
|
Whenever you add a new printf-style function, i.e., one with a format
|
|
string argument and following "..." in its prototype, be sure to use
|
|
gcc's printf attribute directive in the prototype.
|
|
|
|
This makes it so gcc's -Wformat and -Wformat-security options can do
|
|
their jobs and cross-check format strings with the number and types
|
|
of arguments.
|