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

[Philippe Mathieu-Daudé]

On 4/10/20 3:08 PM, Stefano Garzarella wrote:
> 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:

Alex, if possible can you amend this info please?

<---

> (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!

> Thanks to Philippe, I tried this patch and it solves my issue:
>
> Tested-by: Stefano Garzarella <address@hidden>
>
> Thanks,
> Stefano