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

[Stefano Garzarella]

On Sat, Apr 11, 2020 at 01:58:07PM +0100, Alex Bennée wrote:
> 
> Stefano Garzarella <address@hidden> writes:
> 
> > 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)
> 
> I'll see if the new gdb testcases can be generalised - they would have
> caught these snafus.

Yeah, that would be great!

Thanks,
Stefano