Re: [PATCH v1 09/11] gdbstub: i386: Fix gdb_get_reg16() parameter to unbreak gdb

["Alex Bennée" <alex.bennee@linaro.org>]

Stefano Garzarella <sgarzare@redhat.com> writes:

> On Thu, Apr 09, 2020 at 10:15:27PM +0100, Alex Bennée wrote:
>> From: Peter Xu <peterx@redhat.com>
>> 
>> We should only pass in gdb_get_reg16() with the GByteArray* object
>> itself, no need to shift.  Without this patch, gdb remote attach will
>> crash QEMU.
>> 
>> Fixes: a010bdbe719 ("extend GByteArray to read register helpers")
>> Signed-off-by: Peter Xu <peterx@redhat.com>
>> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>> Message-Id: <20200409164954.36902-3-peterx@redhat.com>
>> ---
>>  target/i386/gdbstub.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/target/i386/gdbstub.c b/target/i386/gdbstub.c
>> index f3d23b614ee..b98a99500ae 100644
>> --- a/target/i386/gdbstub.c
>> +++ b/target/i386/gdbstub.c
>> @@ -106,7 +106,7 @@ int x86_cpu_gdb_read_register(CPUState *cs, GByteArray *mem_buf, int n)
>>      } else if (n >= IDX_FP_REGS && n < IDX_FP_REGS + 8) {
>>          floatx80 *fp = (floatx80 *) &env->fpregs[n - IDX_FP_REGS];
>>          int len = gdb_get_reg64(mem_buf, cpu_to_le64(fp->low));
>> -        len += gdb_get_reg16(mem_buf + len, cpu_to_le16(fp->high));
>> +        len += gdb_get_reg16(mem_buf, cpu_to_le16(fp->high));
>>          return len;
>>      } else if (n >= IDX_XMM_REGS && n < IDX_XMM_REGS + CPU_NB_REGS) {
>>          n -= IDX_XMM_REGS;
>> -- 
>> 2.20.1
>> 
>>
>
> I had the following issue while attaching to qemu started with gdbserver
> listening:
>
> (gdb) target remote :1234
> Remote debugging using :1234
> Remote communication error.  Target disconnected.: Connection reset by peer.
>
> $ qemu-system-x86_64 -m 1G -smp 4 ... -s
> ERROR:qemu/gdbstub.c:1843:handle_read_all_regs: assertion failed: (len == gdbserver_state.mem_buf->len)
> Bail out! ERROR:qemu/gdbstub.c:1843:handle_read_all_regs: assertion
> failed: (len == gdbserver_state.mem_buf->len)

I'll see if the new gdb testcases can be generalised - they would have
caught these snafus.

>
>
> Thanks to Philippe, I tried this patch and it solves my issue:
>
> Tested-by: Stefano Garzarella <sgarzare@redhat.com>
>
> Thanks,
> Stefano


-- 
Alex Bennée