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.
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| 1 | # Head objects | ||
| 2 | # | ||
| 3 | # The objects listed here are placed at the head of vmlinux. A typical use-case | ||
| 4 | # is an object that contains the entry point. This is kept for compatibility | ||
| 5 | # with head-y, which Kbuild used to support. | ||
| 6 | # | ||
| 7 | # A counter approach is to control the section placement by the linker script. | ||
| 8 | # The code marked as __HEAD goes into the ".head.text" section, which is placed | ||
| 9 | # before the normal ".text" section. | ||
| 10 | # | ||
| 11 | # If you can achieve the correct code ordering by linker script, please delete | ||
| 12 | # the entry from this file. | ||
| 13 | # | ||
| 14 | arch/alpha/kernel/head.o | ||
| 15 | arch/arc/kernel/head.o | ||
| 16 | arch/arm/kernel/head-nommu.o | ||
| 17 | arch/arm/kernel/head.o | ||
| 18 | arch/arm64/kernel/head.o | ||
| 19 | arch/csky/kernel/head.o | ||
| 20 | arch/hexagon/kernel/head.o | ||
| 21 | arch/ia64/kernel/head.o | ||
| 22 | arch/loongarch/kernel/head.o | ||
| 23 | arch/m68k/68000/head.o | ||
| 24 | arch/m68k/coldfire/head.o | ||
| 25 | arch/m68k/kernel/head.o | ||
| 26 | arch/m68k/kernel/sun3-head.o | ||
| 27 | arch/microblaze/kernel/head.o | ||
| 28 | arch/mips/kernel/head.o | ||
| 29 | arch/nios2/kernel/head.o | ||
| 30 | arch/openrisc/kernel/head.o | ||
| 31 | arch/parisc/kernel/head.o | ||
| 32 | arch/powerpc/kernel/head_40x.o | ||
| 33 | arch/powerpc/kernel/head_44x.o | ||
| 34 | arch/powerpc/kernel/head_64.o | ||
| 35 | arch/powerpc/kernel/head_8xx.o | ||
| 36 | arch/powerpc/kernel/head_book3s_32.o | ||
| 37 | arch/powerpc/kernel/head_fsl_booke.o | ||
| 38 | arch/powerpc/kernel/entry_64.o | ||
| 39 | arch/powerpc/kernel/fpu.o | ||
| 40 | arch/powerpc/kernel/vector.o | ||
| 41 | arch/powerpc/kernel/prom_init.o | ||
| 42 | arch/riscv/kernel/head.o | ||
| 43 | arch/s390/kernel/head64.o | ||
| 44 | arch/sh/kernel/head_32.o | ||
| 45 | arch/sparc/kernel/head_32.o | ||
| 46 | arch/sparc/kernel/head_64.o | ||
| 47 | arch/x86/kernel/head_32.o | ||
| 48 | arch/x86/kernel/head_64.o | ||
| 49 | arch/x86/kernel/head32.o | ||
| 50 | arch/x86/kernel/head64.o | ||
| 51 | arch/x86/kernel/ebda.o | ||
| 52 | arch/x86/kernel/platform-quirks.o | ||
| 53 | arch/xtensa/kernel/head.o | ||