ITS#7191 Align dirty MDB pages on the stack

diff --git a/libraries/libmdb/mdb.c b/libraries/libmdb/mdb.c
index 88970e2a10f3feeb922cb6e8026777051af5ea89..5fa72e65ce4c0af2be555d573b60b2884123f958 100644 (file)
--- a/libraries/libmdb/mdb.c
+++ b/libraries/libmdb/mdb.c
@@ -764,6 +764,20 @@ typedef struct MDB_meta {
        txnid_t         mm_txnid;                       /**< txnid that committed this page */
 } MDB_meta;
 
+       /** Buffer for a stack-allocated dirty page.
+        *      The members define size and alignment, and silence type
+        *      aliasing warnings.  They are not used directly; that could
+        *      mean incorrectly using several union members in parallel.
+        */
+typedef union MDB_pagebuf {
+       char            mb_raw[MDB_PAGESIZE];
+       MDB_page        mb_page;
+       struct {
+               char            mm_pad[PAGEHDRSZ];
+               MDB_meta        mm_meta;
+       } mb_metabuf;
+} MDB_pagebuf;
+
        /** Auxiliary DB info.
         *      The information here is mostly static/read-only. There is
         *      only a single copy of this record in the environment.
@@ -2050,7 +2064,7 @@ done:
 static int
 mdb_env_read_header(MDB_env *env, MDB_meta *meta)
 {
-       char             page[MDB_PAGESIZE];
+       MDB_pagebuf     pbuf;
        MDB_page        *p;
        MDB_meta        *m;
        int              rc, err;
@@ -2059,9 +2073,9 @@ mdb_env_read_header(MDB_env *env, MDB_meta *meta)
         */
 
 #ifdef _WIN32
-       if (!ReadFile(env->me_fd, page, MDB_PAGESIZE, (DWORD *)&rc, NULL) || rc == 0)
+       if (!ReadFile(env->me_fd, &pbuf, MDB_PAGESIZE, (DWORD *)&rc, NULL) || rc == 0)
 #else
-       if ((rc = read(env->me_fd, page, MDB_PAGESIZE)) == 0)
+       if ((rc = read(env->me_fd, &pbuf, MDB_PAGESIZE)) == 0)
 #endif
        {
                return ENOENT;
@@ -2074,7 +2088,7 @@ mdb_env_read_header(MDB_env *env, MDB_meta *meta)
                return err;
        }
 
-       p = (MDB_page *)page;
+       p = (MDB_page *)&pbuf;
 
        if (!F_ISSET(p->mp_flags, P_META)) {
                DPRINTF("page %zu not a meta page", p->mp_pgno);
@@ -3996,7 +4010,7 @@ mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
        unsigned int mcount = 0;
        size_t nsize;
        int rc, rc2;
-       char pbuf[MDB_PAGESIZE];
+       MDB_pagebuf pbuf;
        char dbuf[MAXKEYSIZE+1];
        unsigned int nflags;
        DKBUF;
@@ -4092,7 +4106,7 @@ more:
                                /* create a fake page for the dup items */
                                memcpy(dbuf, dkey.mv_data, dkey.mv_size);
                                dkey.mv_data = dbuf;
-                               fp = (MDB_page *)pbuf;
+                               fp = (MDB_page *)&pbuf;
                                fp->mp_pgno = mc->mc_pg[mc->mc_top]->mp_pgno;
                                fp->mp_flags = P_LEAF|P_DIRTY|P_SUBP;
                                fp->mp_lower = PAGEHDRSZ;
@@ -4108,7 +4122,7 @@ more:
                                do_sub = 1;
                                rdata = &xdata;
                                xdata.mv_size = fp->mp_upper;
-                               xdata.mv_data = pbuf;
+                               xdata.mv_data = fp;
                                flags |= F_DUPDATA;
                                goto new_sub;
                        }
@@ -4161,8 +4175,8 @@ more:
                                        /* no, just grow it */
                                        rdata = &xdata;
                                        xdata.mv_size = NODEDSZ(leaf) + offset;
-                                       xdata.mv_data = pbuf;
-                                       mp = (MDB_page *)pbuf;
+                                       xdata.mv_data = &pbuf;
+                                       mp = (MDB_page *)&pbuf;
                                        mp->mp_pgno = mc->mc_pg[mc->mc_top]->mp_pgno;
                                        flags |= F_DUPDATA;
                                }