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mdbx: avoid 4-byte aligned (i.e. unaligned) access to 64-bit integers.

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Historically, the page header provides 4-byte data alignment.
Therefore, unfortunately, the meta page data is also aligned on a 4-byte boundary, but contains 64-bit values.

This commit eliminates potentially unsafe access (SPARC, MIPS, etc) to these 64-bit values aligned on a 4-byte boundary.
Thus, a build with the `-fsanitize=undefined` now passes the tests both with CLANG 11 and GCC 10.

Change-Id: Ie441103e53ed96fd40507d8c0be0689e3fee69f5
This commit is contained in:
Leonid Yuriev
2020-12-01 20:23:23 +03:00
parent adcb052915
commit a8ed534cd3
2 changed files with 105 additions and 76 deletions
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13
src/internals.h
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@@ -307,10 +307,10 @@ typedef struct mdbx_geo_t {
typedef struct MDBX_meta {
/* Stamp identifying this as an MDBX file.
* It must be set to MDBX_MAGIC with MDBX_DATA_VERSION. */
uint64_t mm_magic_and_version;
uint32_t mm_magic_and_version[2];
/* txnid that committed this page, the first of a two-phase-update pair */
mdbx_safe64_t mm_txnid_a;
uint32_t mm_txnid_a[2];
uint16_t mm_extra_flags; /* extra DB flags, zero (nothing) for now */
uint8_t mm_validator_id; /* ID of checksum and page validation method,
@@ -330,17 +330,18 @@ typedef struct MDBX_meta {
#define MDBX_DATASIGN_NONE 0u
#define MDBX_DATASIGN_WEAK 1u
#define SIGN_IS_STEADY(sign) ((sign) > MDBX_DATASIGN_WEAK)
#define META_IS_STEADY(meta) SIGN_IS_STEADY((meta)->mm_datasync_sign)
volatile uint64_t mm_datasync_sign;
#define META_IS_STEADY(meta) \
SIGN_IS_STEADY(unaligned_peek_u64(4, (meta)->mm_datasync_sign))
uint32_t mm_datasync_sign[2];
/* txnid that committed this page, the second of a two-phase-update pair */
mdbx_safe64_t mm_txnid_b;
uint32_t mm_txnid_b[2];
/* Number of non-meta pages which were put in GC after COW. May be 0 in case
* DB was previously handled by libmdbx without corresponding feature.
* This value in couple with mr_snapshot_pages_retired allows fast estimation
* of "how much reader is restraining GC recycling". */
uint64_t mm_pages_retired;
uint32_t mm_pages_retired[2];
/* The analogue /proc/sys/kernel/random/boot_id or similar to determine
* whether the system was rebooted after the last use of the database files.