Re: [PATCH] Disallow pseudo-registers in agent expression.

Jim Blandy
2008-01-29T01:28:33Z

On Jan 28, 2008 3:51 PM, andrzej zaborowski <balrogg@gmail.com> wrote:
> On 27/01/2008, Jim Blandy <jimb@red-bean.com> wrote:
> > On some targets, all the user-visible registers are pseudo-registers.
> > What we need is a gdbarch method (optional) that the tracepoint code
> > could call, passing it a struct agent_expr and a pseudo-register
> > number, to have the architecture code append the appropriate bytecodes
> > to access that register.
>
> That's ofcourse doable but sounds tough and bug-prone. The mapping of
> numbers to raw registers is to some extent obvious and unlikely to
> change, while the pseudo-registers may change with gdb version so the
> target has more gdb version dependence.

I'm not sure I expressed myself well. I was imagining something like this:

*** ax-gdb.c 07 Jan 2008 08:31:13 -0800 1.40
--- ax-gdb.c 28 Jan 2008 17:21:28 -0800
***************
*** 1607,1615 ****
if (reg == -1)
internal_error (__FILE__, __LINE__,
_("Register $%s not available"), name);
! value->kind = axs_lvalue_register;
! value->u.reg = reg;
! value->type = register_type (current_gdbarch, reg);
}
break;

--- 1607,1627 ----
if (reg == -1)
internal_error (__FILE__, __LINE__,
_("Register $%s not available"), name);
! if (reg < gdbarch_num_regs (current_gdbarch))
! {
! value->kind = axs_lvalue_register;
! value->u.reg = reg;
! value->type = register_type (current_gdbarch, reg);
! }
! else
! {
! /* It's a pseudo-register reference; ask the architecture
! to generate appropriate bytecode for it. */
! if (! gdbarch_gen_pseudo_reg_ax (current_gdbarch, ax, value, reg))
! error (_("Couldn't generate agent expression"
! " to refer to register '%s'"),
! gdbarch_register_name (current_gdbarch, reg));
! }
}
break;

This seems pretty reasonable to me: only the architecture knows how
pseudo-register values are computed from the raw register values --- a
pseudo-register might be two raw registers spliced together, for
example --- so only the architecture knows the right agent bytecode to
generate.