diff options
| -rw-r--r-- | Misc/SpecialBuilds.txt | 52 | ||||
| -rw-r--r-- | Objects/obmalloc.c | 2 |
2 files changed, 53 insertions, 1 deletions
diff --git a/Misc/SpecialBuilds.txt b/Misc/SpecialBuilds.txt index 0551c8e..0851aa5 100644 --- a/Misc/SpecialBuilds.txt +++ b/Misc/SpecialBuilds.txt @@ -60,6 +60,58 @@ envar PYTHONDUMPREFS --------------------------------------------------------------------------- PYMALLOC_DEBUG +When pymalloc is enabled (WITH_PYMALLOC is defined), calls to the PyObject_ +memory routines are handled by Python's own small-object allocator, while +calls to the PyMem_ memory routines are directed to the system malloc/ +realloc/free. If PYMALLOC_DEBUG is also defined, calls to both PyObject_ +and PyMem_ memory routines are directed to a special debugging mode of +Python's small-object allocator. + +This mode fills dynamically allocated memory blocks with special, +recognizable bit patterns, and adds debugging info on each end of +dynamically allocated memory blocks. The special bit patterns are: + +#define CLEANBYTE 0xCB /* clean (newly allocated) memory */ +#define DEADBYTE 0xDB /* dead (newly freed) memory */ +#define FORBIDDENBYTE 0xFB /* fordidden -- untouchable bytes */ + +Strings of these bytes are unlikely to be valid addresses, floats, or 7-bit +ASCII strings. + +8 bytes are added at each end of each block of N bytes requested. The +memory layout is like so, where p represents the address returned by a +malloc-like or realloc-like function: + +p[-8:-4] + Number of bytes originally asked for. 4-byte unsigned integer, + big-endian (easier to read in a memory dump). +p[-4:0] + Copies of FORBIDDENBYTE. Used to catch under- writes and reads. +p[0:N] + The requested memory, filled with copies of CLEANBYTE. + Used to catch reference to uninitialized memory. + When a realloc-like function is called requesting a larger memory + block, the new excess bytes are also filled with CLEANBYTE. + When a free-like function is called, these are overwritten with + DEADBYTE, to catch reference to free()ed memory. When a realloc- + like function is called requesting a smaller memory block, the excess + old bytes are also filled with DEADBYTE. +p[N:N+4] + Copies of FORBIDDENBYTE. Used to catch over- writes and reads. +p[N+4:N+8] + A serial number, incremented by 1 on each call to a malloc-like or + realloc-like function. + 4-byte unsigned integer, big-endian. + If "bad memory" is detected later, the serial number gives an + excellent way to set a breakpoint on the next run, to capture the + instant at which this block was passed out. + +A malloc-like or free-like function first checks that the FORBIDDENBYTEs +at each end are intact. If they've been altered, diagnostic output is +written to stderr, and the program is aborted by Py_FatalError(). + +Note that PYMALLOC_DEBUG requires WITH_PYMALLOC. + Special gimmicks: envar PYTHONMALLOCSTATS diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c index 14f9e25..22481ad 100644 --- a/Objects/obmalloc.c +++ b/Objects/obmalloc.c @@ -881,7 +881,7 @@ PyObject_Free(void *p) #undef DEADBYTE #undef FORBIDDENBYTE #define CLEANBYTE 0xCB /* clean (newly allocated) memory */ -#define DEADBYTE 0xDB /* deed (newly freed) memory */ +#define DEADBYTE 0xDB /* dead (newly freed) memory */ #define FORBIDDENBYTE 0xFB /* untouchable bytes at each end of a block */ static ulong serialno = 0; /* incremented on each debug {m,re}alloc */ |