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kbuild: remove head-y syntax

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Kbuild puts the objects listed in head-y at the head of vmlinux.
Conventionally, we do this for head*.S, which contains the kernel entry
point.

A counter approach is to control the section order by the linker script.
Actually, the code marked as __HEAD goes into the ".head.text" section,
which is placed before the normal ".text" section.

I do not know if both of them are needed. From the build system
perspective, head-y is not mandatory. If you can achieve the proper code
placement by the linker script only, it would be cleaner.

I collected the current head-y objects into head-object-list.txt. It is
a whitelist. My hope is it will be reduced in the long run.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
This commit is contained in:
Masahiro Yamada
2022-09-25 03:19:15 +09:00
parent 3216484550
commit ce697ccee1
24 changed files with 60 additions and 67 deletions
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9
Documentation/kbuild/makefiles.rst
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@@ -1070,8 +1070,7 @@ When kbuild executes, the following steps are followed (roughly):
- The values of the above variables are expanded in arch/$(SRCARCH)/Makefile.
5) All object files are then linked and the resulting file vmlinux is
located at the root of the obj tree.
The very first objects linked are listed in head-y, assigned by
arch/$(SRCARCH)/Makefile.
The very first objects linked are listed in scripts/head-object-list.txt.
6) Finally, the architecture-specific part does any required post processing
and builds the final bootimage.
- This includes building boot records
@@ -1219,6 +1218,9 @@ When kbuild executes, the following steps are followed (roughly):
All object files for vmlinux. They are linked to vmlinux in the same
order as listed in KBUILD_VMLINUX_OBJS.
The objects listed in scripts/head-object-list.txt are exceptions;
they are placed before the other objects.
KBUILD_VMLINUX_LIBS
All .a "lib" files for vmlinux. KBUILD_VMLINUX_OBJS and
@@ -1262,8 +1264,7 @@ When kbuild executes, the following steps are followed (roughly):
machinery is all architecture-independent.
head-y, core-y, libs-y, drivers-y
$(head-y) lists objects to be linked first in vmlinux.
core-y, libs-y, drivers-y
$(libs-y) lists directories where a lib.a archive can be located.