m68k: gdbstub crashing setting float register on cfv4e cpu

[Philippe Mathieu-Daudé]

gdbstub/m68k seems broken with floats, previous to refactor commit
a010bdbe719 ("extend GByteArray to read register helpers").

HEAD at 6fb1603aa2:

$ qemu-system-m68k -s -S -cpu cfv4e

---[GUEST]---

(gdb) set architecture m68k:cfv4e
The target architecture is assumed to be m68k:cfv4e
(gdb) target remote 172.17.0.1:1234
Remote debugging using 172.17.0.1:1234
(gdb) info float
fp0            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
fp1            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
fp2            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
fp3            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
fp4            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
fp5            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
fp6            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
fp7            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
fpcontrol      0x0                 0
fpstatus       0x0                 0
fpiaddr        0x0                 0x0
(gdb) set $fp0=1
Remote communication error.  Target disconnected.: Connection reset by peer.

---[HOST]---

30279@1586881511.897231:gdbstub_io_command Received: P12=000000000000f03f
30279@1586881511.897293:gdbstub_io_reply Sent: OK
30279@1586881511.897593:gdbstub_io_got_ack Got ACK
30279@1586881511.897837:gdbstub_io_command Received: g
Aborted (core dumped)

(gdb) bt
#1  0x00007ffff514e895 in abort () at /lib64/libc.so.6
#2  0x00005555556a9548 in roundAndPackFloat64 (zSign=0 '\000', zExp=0,
zSig=0, status=0x7fffffff9b20) at fpu/softfloat.c:3756
#3  0x00005555556ad2bb in floatx80_to_float64 (a=...,
status=0x7fffffff9b20) at fpu/softfloat.c:5659
#4  0x000055555573a6c7 in cf_fpu_gdb_get_reg
    (env=0x555555fb58d0, mem_buf=0x7fffffff9c7c
"\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377",
n=0) at target/m68k/helper.c:75
#5  0x00005555556bd866 in gdb_read_register
    (cpu=0x555555fad250, mem_buf=0x7fffffff9c7c
"\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377\177\377\377\377\377\377\377\377",
reg=18) at gdbstub.c:896
#6  0x00005555556bf665 in handle_read_all_regs (gdb_ctx=0x7fffffff9c20,
user_ctx=0x0) at gdbstub.c:1813
#7  0x00005555556bead0 in process_string_cmd (s=0x5555564bb000,
user_ctx=0x0, data=0x5555564bb01c "g", cmds=0x555555bf5880
<read_all_regs_cmd_desc>, num_cmds=1) at gdbstub.c:1477
#8  0x00005555556beb45 in run_cmd_parser (s=0x5555564bb000,
data=0x5555564bb01c "g", cmd=0x555555bf5880 <read_all_regs_cmd_desc>) at
gdbstub.c:1493
#9  0x00005555556c093a in gdb_handle_packet (s=0x5555564bb000,
line_buf=0x5555564bb01c "g") at gdbstub.c:2596
#10 0x00005555556c15b7 in gdb_read_byte (s=0x5555564bb000, ch=55 '7') at
gdbstub.c:2932
#11 0x00005555556c17ea in gdb_chr_receive (opaque=0x5555564bb000,
buf=0x7fffffffbde0 "$g#67", '0' <repeats 12 times>,
"f03f#5f\347\372\340\366\377\177", size=5) at gdbstub.c:3170
#12 0x000055555595e986 in qemu_chr_be_write_impl (s=0x55555622eac0,
buf=0x7fffffffbde0 "$g#67", '0' <repeats 12 times>,
"f03f#5f\347\372\340\366\377\177", len=5) at chardev/char.c:183
#13 0x000055555595e9ea in qemu_chr_be_write (s=0x55555622eac0,
buf=0x7fffffffbde0 "$g#67", '0' <repeats 12 times>,
"f03f#5f\347\372\340\366\377\177", len=5) at chardev/char.c:195
#14 0x0000555555967734 in tcp_chr_read (chan=0x555555e21290,
cond=G_IO_IN, opaque=0x55555622eac0) at chardev/char-socket.c:525
#15 0x0000555555982fb4 in qio_channel_fd_source_dispatch
(source=0x555556493200, callback=0x555555967585 <tcp_chr_read>,
user_data=0x55555622eac0) at io/channel-watch.c:84
#16 0x00007ffff7c42ecd in g_main_context_dispatch () at
/lib64/libglib-2.0.so.0
#17 0x00005555559ec20c in glib_pollfds_poll () at util/main-loop.c:219
#18 0x00005555559ec286 in os_host_main_loop_wait (timeout=14976775) at
util/main-loop.c:242
#19 0x00005555559ec38b in main_loop_wait (nonblocking=0) at
util/main-loop.c:518
#20 0x00005555557163dd in qemu_main_loop () at softmmu/vl.c:1665
#21 0x0000555555988d21 in main (argc=7, argv=0x7fffffffd078,
envp=0x7fffffffd0b8) at softmmu/main.c:49