Re: [PATCH v2] x86/boot: Handle better alignment for 32 bit code

[Frediano Ziglio <frediano.ziglio@xxxxxxxxx>]

ping

On Tue, Jan 14, 2025 at 11:54 AM Frediano Ziglio
<frediano.ziglio@xxxxxxxxx> wrote:
>
> Output file didn't have correct alignment.
> Allows alignment into data or code up to 2mb.
> Intermediate object files are kept in order to copy alignment
> from object produced by the linker and final object (produced
> by combine_two_binaries.py script).
>
> Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
> ---
>  xen/arch/x86/boot/Makefile        | 12 ++++++++----
>  xen/tools/combine_two_binaries.py |  7 ++++++-
>  2 files changed, 14 insertions(+), 5 deletions(-)
>
> Changes since v1:
> - Improve comments and description.
>
> diff --git a/xen/arch/x86/boot/Makefile b/xen/arch/x86/boot/Makefile
> index 13d4583173..a56d8a7e0f 100644
> --- a/xen/arch/x86/boot/Makefile
> +++ b/xen/arch/x86/boot/Makefile
> @@ -40,8 +40,12 @@ LD32 := $(LD) $(subst x86_64,i386,$(LDFLAGS_DIRECT))
>  # are affected by both text_diff and text_gap.  Ensure the sum of gap and 
> diff
>  # is greater than 2^16 so that any 16bit relocations if present in the object
>  # file turns into a build-time error.
> -text_gap := 0x010200
> -text_diff := 0x408020
> +# As gap will affect the output section size it should not be huge to avoid 
> the
> +# creation of huge files.
> +# The sum of gap and diff will affect the possible alignment so should be a
> +# multiple of the possible alignment.
> +text_gap := 0x01c240
> +text_diff := 0x7e3dc0
>
>  $(obj)/build32.base.lds: AFLAGS-y += -DGAP=$(text_gap) 
> -DTEXT_DIFF=$(text_diff)
>  $(obj)/build32.offset.lds: AFLAGS-y += -DGAP=$(text_gap) 
> -DTEXT_DIFF=$(text_diff) -DAPPLY_OFFSET
> @@ -69,7 +73,6 @@ $(obj)/built-in-32.%.bin: $(obj)/build32.%.lds 
> $(obj)/built-in-32.tmp.o
>         $(LD32) $(orphan-handling-y) -N -T $< -o $(@:bin=o) $(filter %.o,$^)
>         $(NM) -p --format=bsd $(@:bin=o) > $(@:bin=map)
>         $(OBJCOPY) -j .text -O binary $(@:bin=o) $@
> -       rm -f $(@:bin=o)
>
>  quiet_cmd_combine = GEN     $@
>  cmd_combine = \
> @@ -80,6 +83,7 @@ cmd_combine = \
>                --bin1      $(obj)/built-in-32.base.bin \
>                --bin2      $(obj)/built-in-32.offset.bin \
>                --map       $(obj)/built-in-32.base.map \
> +              --align     $(shell $(OBJDUMP) -h 
> $(obj)/built-in-32.base.o|sed '/text.*2\*\*/ {s/.*2\*\*//;p;}; d') \
>                --exports   cmdline_parse_early,reloc,reloc_trampoline32 \
>                --output    $@
>
> @@ -90,4 +94,4 @@ $(obj)/built-in-32.S: $(obj)/built-in-32.base.bin 
> $(obj)/built-in-32.offset.bin
>                        $(srctree)/tools/combine_two_binaries.py FORCE
>         $(call if_changed,combine)
>
> -clean-files := built-in-32.*.bin built-in-32.*.map build32.*.lds
> +clean-files := built-in-32.*.bin built-in-32.*.map built-in-32.*.o 
> build32.*.lds
> diff --git a/xen/tools/combine_two_binaries.py 
> b/xen/tools/combine_two_binaries.py
> index 581e57cbc0..8e587c24fb 100755
> --- a/xen/tools/combine_two_binaries.py
> +++ b/xen/tools/combine_two_binaries.py
> @@ -26,6 +26,10 @@ parser.add_argument('--text-diff', dest='text_diff',
>                      required=True,
>                      type=auto_int,
>                      help='Difference between code section start')
> +parser.add_argument('--align', dest='align',
> +                    default=2,
> +                    type=auto_int,
> +                    help='Alignment in power of 2')
>  parser.add_argument('--output', dest='output',
>                      help='Output file')
>  parser.add_argument('--map', dest='mapfile',
> @@ -93,7 +97,7 @@ if size1 > size2:
>      file1, file2 = file2, file1
>      size1, size2 = size2, size1
>  if size2 != size1 + gap:
> -    raise Exception('File sizes do not match')
> +    raise Exception('File sizes do not match %d != %d + %d' % (size2, size1, 
> gap))
>  del size2
>
>  file1.seek(0, 0)
> @@ -219,6 +223,7 @@ print('''/*
>   * File autogenerated by combine_two_binaries.py DO NOT EDIT
>   */''', file=out)
>  print('\t' + args.section_header, file=out)
> +print('\t.p2align\t' + str(args.align), file=out)
>  print('obj32_start:', file=out)
>  output(out)
>  print('\n\t.section .note.GNU-stack,"",@progbits', file=out)
> --
> 2.34.1
>