[PATCH-for-9.0? 2/2] hw/net/lan9118: Fix overflow in TX FIFO

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

When the TX FIFO is full, raise the TX Status FIFO Overflow (TXSO)
flag, "Generated when the TX Status FIFO overflows" [*].

Broken since model introduction in commit 2a42499017
("LAN9118 emulation").

When using the reproducer from
https://gitlab.com/qemu-project/qemu/-/issues/2267 we get:

  hw/net/lan9118.c:798:17: runtime error:
  index 2048 out of bounds for type 'uint8_t[2048]' (aka 'unsigned char[2048]')
    #0 0x563ec9a057b1 in tx_fifo_push hw/net/lan9118.c:798:43
    #1 0x563ec99fbb28 in lan9118_writel hw/net/lan9118.c:1042:9
    #2 0x563ec99f2de2 in lan9118_16bit_mode_write hw/net/lan9118.c:1205:9
    #3 0x563ecbf78013 in memory_region_write_accessor system/memory.c:497:5
    #4 0x563ecbf776f5 in access_with_adjusted_size system/memory.c:573:18
    #5 0x563ecbf75643 in memory_region_dispatch_write system/memory.c:1521:16
    #6 0x563ecc01bade in flatview_write_continue_step system/physmem.c:2713:18
    #7 0x563ecc01b374 in flatview_write_continue system/physmem.c:2743:19
    #8 0x563ecbff1c9b in flatview_write system/physmem.c:2774:12
    #9 0x563ecbff1768 in address_space_write system/physmem.c:2894:18
    ...

[*] LAN9118 DS00002266B.pdf, Table 5.3.3 "INTERRUPT STATUS REGISTER"

Reported-by: Will Lester
Reported-by: Chuhong Yuan <hslester96@gmail.com>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2267
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 hw/net/lan9118.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/hw/net/lan9118.c b/hw/net/lan9118.c
index 7be0430ac5..7a1367b0bb 100644
--- a/hw/net/lan9118.c
+++ b/hw/net/lan9118.c
@@ -795,8 +795,11 @@ static void tx_fifo_push(lan9118_state *s, uint32_t val)
             /* Documentation is somewhat unclear on the ordering of bytes
                in FIFO words.  Empirical results show it to be little-endian.
                */
-            /* TODO: FIFO overflow checking.  */
             while (n--) {
+                if (s->txp->len == PKT_SIZE) {
+                    s->int_sts |= TXSO_INT;
+                    break;
+                }
                 s->txp->data[s->txp->len] = val & 0xff;
                 s->txp->len++;
                 val >>= 8;
-- 
2.41.0