fd_txn_parse: fail transactions that include an ALT but don't load fr…

…om it.

This is to match Solana Lab's behavior.
Shrinks the max fd_txn_t size by 8 bytes, which has some other
implications.

src/ballet/txn/fd_txn.h

@@ -90,8 +90,9 @@
    take up, including the instruction array and any address tables.  The
    worst-case transaction is a V0 transaction with only two account
    addresses (a program and a fee payer), and tons of empty instructions (no
-   accounts, no data) and as many address table lookups as possible. */
-#define FD_TXN_MAX_SZ                (860UL)
+   accounts, no data) and as many address table lookups loading a single
+   account as possible. */
+#define FD_TXN_MAX_SZ                (852UL)
 
 
 /* FD_TXN_MTU: The maximum size (in bytes, inclusive) of a serialized

src/ballet/txn/fd_txn_parse.c

@@ -202,8 +202,9 @@ fd_txn_parse_core( uchar const             * payload,
       READ_CHECKED_COMPACT_U16( bytes_consumed,            readonly_cnt,             i );     i+=bytes_consumed;
       CHECK_LEFT( readonly_cnt                  );   ulong readonly_off   =          i  ;     i+=readonly_cnt;
 
-      CHECK( writable_cnt<=FD_TXN_ACCT_ADDR_MAX-acct_addr_cnt ); /* implies <256 */
+      CHECK( writable_cnt<=FD_TXN_ACCT_ADDR_MAX-acct_addr_cnt ); /* implies <256 ... */
       CHECK( readonly_cnt<=FD_TXN_ACCT_ADDR_MAX-acct_addr_cnt );
+      CHECK( (ushort)1   <=writable_cnt+readonly_cnt          ); /* ... so the sum can't overflow */
       if( address_tables ) {
         address_tables[ j ].addr_off      = (ushort)addr_off;
         address_tables[ j ].writable_cnt  = (uchar )writable_cnt;

src/ballet/txn/test_txn.c

@@ -8,29 +8,29 @@ FD_STATIC_ASSERT( FD_TXN_MTU<=USHORT_MAX, fd_txn_mtu );
 /* Calculate the max size for an fd_txn_t */
 
 /* A worst-case instruction takes 3B of the payload and is stored as 10 B.  A
-   worst-case address lookup table takes 34B of the payload and is stored as 8B.
+   worst-case address lookup table takes 35B of the payload and is stored as 8B.
    This gives the optimization problem:
     Maximize sizeof(fd_txn_t) + x * sizeof(fd_txn_instr_t) + y * sizeof(fd_txn_acct_addr_lut_t)
     subject to:
           MIN_FIXED_SIZE_SECTION
             + (x>0 ? 32 : 0) + len_compact_u16(x) + 3*x
-            + (y>0 ?  1 : 0) + len_compact_u16(y) + 34*y          <=  1232
+            + (y>0 ?  1 : 0) + len_compact_u16(y) + 35*y          <=  1232
           0 <= x <= FD_TXN_INSTR_MAX
           0 <= y <= FD_TXN_ADDR_TABLE_LOOKUP_MAX
           x, y integers
 
    which has solution (not hard to see by hand):
      x == FD_TXN_INSTR_MAX
-     y == floor((1232 - ... )/34)==25,
-   giving an objective of 860.
+     y == floor((1232 - ... )/35)==24,
+   giving an objective of 852.
 */
 #define MIN_PAYLOAD_SZ( instr_cnt, alt_cnt )                              \
                         ( 1 + FD_TXN_SIGNATURE_SZ                         \
                           + ((alt_cnt) ? 1 : 0) + 3                       \
                           + 1 + ((instr_cnt) ? 2 : 1)*FD_TXN_ACCT_ADDR_SZ \
                           + FD_TXN_BLOCKHASH_SZ                           \
                           + 1 + 3*(instr_cnt)                             \
-                          + 1 + 34*(alt_cnt) )
+                          + 1 + 35*(alt_cnt) )
 
 #define PARSED_SZ( instr_cnt, alt_cnt )                        \
                   sizeof(fd_txn_t)                             \
@@ -43,7 +43,7 @@ FD_STATIC_ASSERT( FD_TXN_MTU<=USHORT_MAX, fd_txn_mtu );
                                  + FD_TXN_BLOCKHASH_SZ       )
 #define WORST_CASE_INSTR_CNT     FD_TXN_INSTR_MAX
 #define WORST_CASE_INSTR_PAYLOAD (1 + WORST_CASE_INSTR_CNT*3 )
-#define WORST_CASE_ALT_CNT       ((1232 - MIN_FIXED_SIZE_SECTION - FD_TXN_ACCT_ADDR_SZ - WORST_CASE_INSTR_PAYLOAD - 1)/(34))
+#define WORST_CASE_ALT_CNT       ((1232 - MIN_FIXED_SIZE_SECTION - FD_TXN_ACCT_ADDR_SZ - WORST_CASE_INSTR_PAYLOAD - 1)/(35))
 FD_STATIC_ASSERT( FD_TXN_MAX_SZ==sizeof(fd_txn_t) +
     WORST_CASE_INSTR_CNT*sizeof(fd_txn_instr_t) +
     WORST_CASE_ALT_CNT*sizeof(fd_txn_acct_addr_lut_t), fd_txn );

src/disco/fd_disco_base.h

@@ -33,7 +33,7 @@
 /* The literal value of FD_TPU_DCACHE_MTU is used in some of the Rust
    shims, so if the value changes, this acts as a reminder to change it
    in the Rust code. */
-FD_STATIC_ASSERT( FD_TPU_DCACHE_MTU==2094UL, tpu_dcache_mtu_check );
+FD_STATIC_ASSERT( FD_TPU_DCACHE_MTU==2086UL, tpu_dcache_mtu_check );
 
 #define FD_NETMUX_SIG_MIN_HDR_SZ    ( 42UL) /* The default header size, which means no vlan tags and no IP options. */
 #define FD_NETMUX_SIG_IGNORE_HDR_SZ (102UL) /* Outside the allowable range, but still fits in 4 bits when compressed */