Re: [PATCH] powerpc/boot: fix broken way to pass CONFIG options

[Oliver]

On Mon, May 13, 2019 at 9:23 PM Masahiro Yamada
<yamada.masahiro@xxxxxxxxxxxxx> wrote:
>
> Commit 5e9dcb6188a4 ("powerpc/boot: Expose Kconfig symbols to wrapper")
> was wrong, but commit e41b93a6be57 ("powerpc/boot: Fix build failures
> with -j 1") was also wrong.
>
> Check-in source files never ever depend on build artifacts.
>
> The correct dependency is:
>
>   $(obj)/serial.o: $(obj)/autoconf.h
>
> However, copying autoconf.h to arch/power/boot/ is questionable
> in the first place.
>
> arch/powerpc/Makefile adopted multiple ways to pass CONFIG options.
>
> arch/powerpc/boot/decompress.c references CONFIG_KERNEL_GZIP and
> CONFIG_KERNEL_XZ, which are passed via the command line.
>
> arch/powerpc/boot/serial.c includes the copied autoconf.h to
> reference a couple of CONFIG options.
>
> Do not do this.
>
> We should have already learned that including autoconf.h from each
> source file is really fragile.
>
> In fact, it is already broken.
>
> arch/powerpc/boot/ppc_asm.h references CONFIG_PPC_8xx, but
> arch/powerpc/boot/utils.S is not given any way to access CONFIG
> options. So, CONFIG_PPC_8xx is never defined here.
>
> Just pass $(LINUXINCLUDE) and remove all broken code.

I'm not sure how safe this is. The original reason for the
CONFIG_KERNEL_XZ hack in the makefile was because the kernel headers
couldn't be included directly. The bootwrapper is compiled with a
32bit toolchain when the kernel is compiled for 64bit big endian
because of older systems with broken firmware that can't load 64bit
ELFs directly. When I added XZ support to the wrapper I did experiment
with including the kernel headers directly and couldn't make it work
reliably. I don't remember what the exact reason was, but I think it
was something to do with the generated headers not always matching
what you would expect when compiling for 32bit. It's also possible I
was just being paranoid. Either way it's about time we found a real
fix...

The stuff in serial.c and ppc_asm.h was added later to work around
other issues without anyone thinking too hard about it. Oh well.

> I also removed the -traditional flag to make include/linux/kconfig.h
> work. I do not understand why it needs to imitate the behavior of
> pre-standard C preprocessors.

I'm not sure why it's there either. The boot wrapper was re-written at
some point so it might just be a hold over from the dawn of time.

> Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> ---
>
>  arch/powerpc/boot/.gitignore |  2 --
>  arch/powerpc/boot/Makefile   | 14 +++-----------
>  arch/powerpc/boot/serial.c   |  1 -
>  3 files changed, 3 insertions(+), 14 deletions(-)
>
> diff --git a/arch/powerpc/boot/.gitignore b/arch/powerpc/boot/.gitignore
> index 32034a0cc554..6610665fcf5e 100644
> --- a/arch/powerpc/boot/.gitignore
> +++ b/arch/powerpc/boot/.gitignore
> @@ -44,5 +44,3 @@ fdt_sw.c
>  fdt_wip.c
>  libfdt.h
>  libfdt_internal.h
> -autoconf.h
> -
> diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
> index 73d1f3562978..b8a82be2af2a 100644
> --- a/arch/powerpc/boot/Makefile
> +++ b/arch/powerpc/boot/Makefile
> @@ -20,9 +20,6 @@
>
>  all: $(obj)/zImage
>
> -compress-$(CONFIG_KERNEL_GZIP) := CONFIG_KERNEL_GZIP
> -compress-$(CONFIG_KERNEL_XZ)   := CONFIG_KERNEL_XZ
> -
>  ifdef CROSS32_COMPILE
>      BOOTCC := $(CROSS32_COMPILE)gcc
>      BOOTAR := $(CROSS32_COMPILE)ar
> @@ -34,7 +31,7 @@ endif
>  BOOTCFLAGS    := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
>                  -fno-strict-aliasing -O2 -msoft-float -mno-altivec -mno-vsx \
>                  -pipe -fomit-frame-pointer -fno-builtin -fPIC -nostdinc \
> -                -D$(compress-y)
> +                $(LINUXINCLUDE)
>
>  ifdef CONFIG_PPC64_BOOT_WRAPPER
>  BOOTCFLAGS     += -m64
> @@ -51,7 +48,7 @@ BOOTCFLAGS    += -mlittle-endian
>  BOOTCFLAGS     += $(call cc-option,-mabi=elfv2)
>  endif
>
> -BOOTAFLAGS     := -D__ASSEMBLY__ $(BOOTCFLAGS) -traditional -nostdinc
> +BOOTAFLAGS     := -D__ASSEMBLY__ $(BOOTCFLAGS) -nostdinc
>
>  BOOTARFLAGS    := -cr$(KBUILD_ARFLAGS)
>
> @@ -202,14 +199,9 @@ $(obj)/empty.c:
>  $(obj)/zImage.coff.lds $(obj)/zImage.ps3.lds : $(obj)/%: $(srctree)/$(src)/%.S
>         $(Q)cp $< $@
>
> -$(srctree)/$(src)/serial.c: $(obj)/autoconf.h
> -
> -$(obj)/autoconf.h: $(obj)/%: $(objtree)/include/generated/%
> -       $(Q)cp $< $@
> -
>  clean-files := $(zlib-) $(zlibheader-) $(zliblinuxheader-) \
>                 $(zlib-decomp-) $(libfdt) $(libfdtheader) \
> -               autoconf.h empty.c zImage.coff.lds zImage.ps3.lds zImage.lds
> +               empty.c zImage.coff.lds zImage.ps3.lds zImage.lds
>
>  quiet_cmd_bootcc = BOOTCC  $@
>        cmd_bootcc = $(BOOTCC) -Wp,-MD,$(depfile) $(BOOTCFLAGS) -c -o $@ $<
> diff --git a/arch/powerpc/boot/serial.c b/arch/powerpc/boot/serial.c
> index b0491b8c0199..9457863147f9 100644
> --- a/arch/powerpc/boot/serial.c
> +++ b/arch/powerpc/boot/serial.c
> @@ -18,7 +18,6 @@
>  #include "stdio.h"
>  #include "io.h"
>  #include "ops.h"
> -#include "autoconf.h"
>
>  static int serial_open(void)
>  {
> --
> 2.17.1
>