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

[Stefano Garzarella]

On Thu, Apr 09, 2020 at 10:15:27PM +0100, Alex Bennée wrote:
> From: Peter Xu <address@hidden>
> 
> 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 <address@hidden>
> Reviewed-by: Philippe Mathieu-Daudé <address@hidden>
> Signed-off-by: Alex Bennée <address@hidden>
> Message-Id: <address@hidden>
> ---
>  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)


Thanks to Philippe, I tried this patch and it solves my issue:

Tested-by: Stefano Garzarella <address@hidden>

Thanks,
Stefano