[PATCH v2 2/2] firmware: Support position independent execution

[Vincent Chen]

On Tue, Mar 16, 2021 at 10:40 AM Jessica Clarke <jrtc27 at jrtc27.com> wrote:
>
> On 16 Mar 2021, at 01:59, Vincent Chen <vincent.chen at sifive.com> wrote:
> >
> > On Mon, Mar 15, 2021 at 5:58 PM Anup Patel <anup at brainfault.org> wrote:
> >>
> >> On Mon, Mar 15, 2021 at 3:11 PM Vincent Chen <vincent.chen at sifive.com> wrote:
> >>>
> >>> On Sat, Mar 13, 2021 at 12:13 AM Anup Patel <anup at brainfault.org> wrote:
> >>>>
> >>>> On Fri, Mar 5, 2021 at 2:35 PM Vincent Chen <vincent.chen at sifive.com> wrote:
> >>>>> diff --git a/firmware/fw_jump.S b/firmware/fw_jump.S
> >>>>> index 5b24f8b..4fb3e0c 100644
> >>>>> --- a/firmware/fw_jump.S
> >>>>> +++ b/firmware/fw_jump.S
> >>>>> @@ -46,6 +46,11 @@ fw_save_info:
> >>>>> fw_next_arg1:
> >>>>> #ifdef FW_JUMP_FDT_ADDR
> >>>>>        li      a0, FW_JUMP_FDT_ADDR
> >>>>> +#ifdef FW_PIC
> >>>>> +       lla     a1, _runtime_offset
> >>>>> +       REG_L   a1, (a1)
> >>>>> +       add     a0, a0, a1
> >>>>> +#endif
> >>>>> #else
> >>>>>        add     a0, a1, zero
> >>>>> #endif
> >>>>> @@ -61,6 +66,11 @@ fw_next_arg1:
> >>>>> fw_next_addr:
> >>>>>        lla     a0, _jump_addr
> >>>>>        REG_L   a0, (a0)
> >>>>> +#ifdef FW_PIC
> >>>>> +       lla     a1, _runtime_offset
> >>>>> +       REG_L   a1, (a1)
> >>>>> +       add     a0, a0, a1
> >>>>> +#endif
> >>>>>        ret
> >>>>
> >>>> The changes in fw_next_addr() breaks the FW_JUMP when
> >>>> FW_PIC=y because FW_JUMP assumes a compile-time
> >>>> fixed address of next booting stage specified by FW_JUMP_ADDR.
> >>>>
> >>>> Similarly, when FW_JUMP_FDT_ADDR is defined FW_JUMP
> >>>> will assume compile-time fixed address of FDT passed to
> >>>> next booting stage.
> >>>>
> >>>> Please drop all changes from fw_jump.S
> >>>>
> >>> OK, I will drop it.
> >
> > Sorry, I forgot to ask a question. Does the assumption of  FW_JUMP
> > also imply that FW_JUMP cannot support PIE mode, right?
>
> No, you can have a PIE FW_JUMP OpenSBI. The problem is that you added relocbase
> to FW_JUMP_ADDR and FW_JUMP_FDT_ADDR when those are platform-defined constants
> regardless of where OpenSBI has been loaded, and so should remain unmodified.
>
> Jess
>
I got it. Thank you for your explanation.