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7cc14ae9d8
This commit also fixes copyright line missed by the automated script. Author: Masahiko Sawada
93 lines
3.5 KiB
C
93 lines
3.5 KiB
C
/*-------------------------------------------------------------------------
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*
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* memdebug.c
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* Declarations used in memory context implementations, not part of the
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* public API of the memory management subsystem.
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*
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*
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* Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/backend/utils/memdebug.c
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*
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*
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* About CLOBBER_FREED_MEMORY:
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*
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* If this symbol is defined, all freed memory is overwritten with 0x7F's.
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* This is useful for catching places that reference already-freed memory.
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*
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* About MEMORY_CONTEXT_CHECKING:
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*
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* Since we usually round request sizes up to the next power of 2, there
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* is often some unused space immediately after a requested data area.
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* Thus, if someone makes the common error of writing past what they've
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* requested, the problem is likely to go unnoticed ... until the day when
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* there *isn't* any wasted space, perhaps because of different memory
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* alignment on a new platform, or some other effect. To catch this sort
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* of problem, the MEMORY_CONTEXT_CHECKING option stores 0x7E just beyond
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* the requested space whenever the request is less than the actual chunk
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* size, and verifies that the byte is undamaged when the chunk is freed.
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*
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*
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* About USE_VALGRIND and Valgrind client requests:
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*
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* Valgrind provides "client request" macros that exchange information with
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* the host Valgrind (if any). Under !USE_VALGRIND, memdebug.h stubs out
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* currently-used macros.
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*
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* When running under Valgrind, we want a NOACCESS memory region both before
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* and after the allocation. The chunk header is tempting as the preceding
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* region, but mcxt.c expects to able to examine the standard chunk header
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* fields. Therefore, we use, when available, the requested_size field and
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* any subsequent padding. requested_size is made NOACCESS before returning
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* a chunk pointer to a caller. However, to reduce client request traffic,
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* it is kept DEFINED in chunks on the free list.
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*
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* The rounded-up capacity of the chunk usually acts as a post-allocation
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* NOACCESS region. If the request consumes precisely the entire chunk,
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* there is no such region; another chunk header may immediately follow. In
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* that case, Valgrind will not detect access beyond the end of the chunk.
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*
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* See also the cooperating Valgrind client requests in mcxt.c.
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "utils/memdebug.h"
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#ifdef RANDOMIZE_ALLOCATED_MEMORY
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/*
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* Fill a just-allocated piece of memory with "random" data. It's not really
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* very random, just a repeating sequence with a length that's prime. What
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* we mainly want out of it is to have a good probability that two palloc's
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* of the same number of bytes start out containing different data.
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*
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* The region may be NOACCESS, so make it UNDEFINED first to avoid errors as
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* we fill it. Filling the region makes it DEFINED, so make it UNDEFINED
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* again afterward. Whether to finally make it UNDEFINED or NOACCESS is
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* fairly arbitrary. UNDEFINED is more convenient for SlabRealloc(), and
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* other callers have no preference.
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*/
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void
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randomize_mem(char *ptr, size_t size)
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{
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static int save_ctr = 1;
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size_t remaining = size;
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int ctr;
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ctr = save_ctr;
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VALGRIND_MAKE_MEM_UNDEFINED(ptr, size);
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while (remaining-- > 0)
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{
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*ptr++ = ctr;
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if (++ctr > 251)
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ctr = 1;
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}
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VALGRIND_MAKE_MEM_UNDEFINED(ptr - size, size);
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save_ctr = ctr;
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}
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#endif /* RANDOMIZE_ALLOCATED_MEMORY */
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