M68K Vectors

Peter LaDow pladow at gmail.com
Fri Jul 26 22:22:56 CEST 2024


Scratch that.  I forgot I hard coded the vector table with 0x400 to
test things.  Restoring _start still results in 0x00000000 for the
reset vector.

On Fri, Jul 26, 2024 at 1:16 PM Peter LaDow <pladow at gmail.com> wrote:
>
> I should mention I was using the gcc-m68k-linux-gnu package on Ubuntu
> 22.04.4, which pulled in gcc-11-m68k-linux-gnu.
>
> I just downloaded the bootlin m68k-coldfire--uclibc--stable-2024.02-1,
> and tried that.  It generates the proper value in the vector table
> (0x400 for _start).  But the call to memset is still bad:
>
> 0000f5da <board_init_f_init_reserve>:
>    f5da:       2f02            movel %d2,%sp at -
>    f5dc:       242f 0008       movel %sp@(8),%d2
>    f5e0:       4878 00c0       pea c0 <_vectors+0xc0>
>    f5e4:       42a7            clrl %sp at -
>    f5e6:       2f02            movel %d2,%sp at -
>    f5e8:       61ff 0001 4622  bsrl 23c0c <_etext+0x138>
>    f5ee:       2f02            movel %d2,%sp at -
>    f5f0:       61ff ffff ffd2  bsrl f5c4 <arch_setup_gd>
>    f5f6:       0682 0000 00c0  addil #192,%d2
>    f5fc:       4fef 0010       lea %sp@(16),%sp
>    f600:       2047            moveal %d7,%a0
>    f602:       2142 00a0       movel %d2,%a0@(160)
>    f606:       241f            movel %sp at +,%d2
>    f608:       4e75            rts
>
> Note "bsrl 23c0c" which points beyond _etext.
>
> On Fri, Jul 26, 2024 at 12:59 PM Fabio Estevam <festevam at gmail.com> wrote:
> >
> > Adding the Coldfire maintainers on Cc.
> >
> > On Fri, Jul 26, 2024 at 4:46 PM Peter LaDow <pladow at gmail.com> wrote:
> > >
> > > After some digging it appears that this is a toolchain issue.  It seems the
> > > linker fixups are sometimes not computed correctly.  For example, in
> > > board_init_f_init_reserve, the object file disassembled has:
> > >
> > > 00000000 <board_init_f_init_reserve>:
> > >   0:   2f02            movel %d2,%sp at -
> > >   2:   242f 0008       movel %sp@(8),%d2
> > >   6:   4878 00c0       pea c0 <board_init_f_init_reserve+0xc0>
> > >   a:   42a7            clrl %sp at -
> > >   c:   2f02            movel %d2,%sp at -
> > >   e:   61ff 0000 0000  bsrl 10 <board_init_f_init_reserve+0x10>
> > >  14:   2f02            movel %d2,%sp at -
> > >  16:   61ff 0000 0000  bsrl 18 <board_init_f_init_reserve+0x18>
> > >  1c:   0682 0000 00c0  addil #192,%d2
> > >  22:   4fef 0010       lea %sp@(16),%sp
> > >  26:   2047            moveal %d7,%a0
> > >  28:   2142 00a0       movel %d2,%a0@(160)
> > >  2c:   241f            movel %sp at +,%d2
> > >  2e:   4e75            rts
> > >
> > > But when I disassemble the final linked u-boot output:
> > >
> > > 0000f646 <board_init_f_init_reserve>:
> > >    f646:       2f02            movel %d2,%sp at -
> > >    f648:       242f 0008       movel %sp@(8),%d2
> > >    f64c:       4878 00c0       pea c0 <_vectors+0xc0>
> > >    f650:       42a7            clrl %sp at -
> > >    f652:       2f02            movel %d2,%sp at -
> > >    f654:       61ff 0001 44da  bsrl 23b30 <_etext+0x138>
> > >    f65a:       2f02            movel %d2,%sp at -
> > >    f65c:       61ff ffff ffd2  bsrl f630 <arch_setup_gd>
> > >    f662:       0682 0000 00c0  addil #192,%d2
> > >    f668:       4fef 0010       lea %sp@(16),%sp
> > >    f66c:       2047            moveal %d7,%a0
> > >    f66e:       2142 00a0       movel %d2,%a0@(160)
> > >    f672:       241f            movel %sp at +,%d2
> > >    f674:       4e75            rts
> > >
> > > Note the pea c0 instruction.  The object file has
> > > board_init_f_init_reserve+0xc0 as the argument, but the final linker has
> > > 0xc0, meaning board_init_f_init_reserve is being set to 0 after linking.
> > >
> > > Also, note the first bsrl instruction, which is not setup correctly
> > > either.  This is a call to memset.  This points to _etext+0x138, which is
> > > not a code region Note that 0x239f8 + 0x138 = 0x23b30.  But in the final
> > > uboot, memset is at 0x1f030.
> > >
> > > In the call to memset(),  objdump shows the relocation:
> > >
> > > RELOCATION RECORDS FOR [.text.board_init_f_init_reserve]:
> > > OFFSET   TYPE              VALUE
> > > 00000010 R_68K_PLT32       memset
> > > 00000018 R_68K_PLT32       arch_setup_gd
> > >
> > > So it seems only when linking outside the same compilation unit that the
> > > relocations aren't set correctly.
> > >
> > > I'm not sure where to look for a solution.  Or how to search for an
> > > answer.  I've done some digging on Google, but nothing points to a clear
> > > answer.  Anyone seen something similar?
> > >
> > > To love for the sake of being loved is human, but to love for the sake of
> > > loving is angelic. -- Alphonse de Lamartine.
> > >
> > >
> > > On Thu, Jul 25, 2024 at 14:35 Peter LaDow <pladow at gmail.com> wrote:
> > > >
> > > > I'm trying to add support for a custom Colfire based board.  I have
> > > > things building, but the final linked vectors in start.S do not point
> > > > to _start.  In start.S I have:
> > > >
> > > > _vectors:
> > > > .long   0x00000000              /* Flash offset is 0 until we setup CS0 */
> > > > .long   _START
> > > >
> > > > .long   _FAULT, _FAULT, _FAULT, _FAULT, _FAULT, _FAULT, _FAULT, _FAULT
> > > > .long   _FAULT, _FAULT, _FAULT, _FAULT, _FAULT, _FAULT, _FAULT, _FAULT
> > > > .long   _FAULT, _FAULT, _FAULT, _FAULT, _FAULT, _FAULT, _FAULT, _FAULT
> > > >
> > > > Dumping the symbols in the final u-boot yields:
> > > >
> > > > $ m68k-linux-gnu-nm -n u-boot
> > > > 00000000 A __fixup_entries
> > > > 00000000 A __got2_entries
> > > > 00000000 t _vectors
> > > > 00000400 T _start
> > > > 0000047e T relocate_code
> > > > 000004ae t fixloop
> > > >
> > > > But then dumping the raw binary:
> > > >
> > > > u-boot:     file format elf32-m68k
> > > >
> > > > Contents of section .text:
> > > > 00000 00000000 00000000 00000516 00000516  ................
> > > > 00010 00000516 00000516 00000516 00000516  ................
> > > > 00020 00000516 00000516 00000516 00000516  ................
> > > > 00030 00000516 00000516 00000516 00000516  ................
> > > >
> > > > Note at offset 4 it is 0x00000000, not 0x00000400 as I'd expect.
> > > >
> > > > The final linker script has:
> > > >
> > > > OUTPUT_ARCH(m68k)
> > > > ENTRY(_start)
> > > > SECTIONS
> > > > {
> > > > .text :
> > > > {
> > > >  arch/m68k/cpu/mcf548x/start.o (.text*)
> > > >  . = DEFINED(env_offset) ? env_offset : .; env/embedded.o(.text*);
> > > >  *(.text*)
> > > > }
> > > >
> > > >
> > > > It is difficult to search the archives, and so far I haven't found
> > > > anything.  Any help would be appreciated.
> > > >
> > > > --
> > > > To love for the sake of being loved is human, but to love for the sake
> > > > of loving is angelic. -- Alphonse de Lamartine.
>
>
>
> --
> To love for the sake of being loved is human, but to love for the sake
> of loving is angelic. -- Alphonse de Lamartine.



-- 
To love for the sake of being loved is human, but to love for the sake
of loving is angelic. -- Alphonse de Lamartine.


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