Search notes:

arch/x86/boot/compressed/piggy.S

arch/x86/boot/compressed/piggy.S is created when the kernel is made.

piggy.S is used to create arch/x86/boot/compressed/piggy.o which in turn is a requisite to create arch/x86/boot/compressed/vmlinux.

piggy.S is created with the mkpiggy command (See also mkpiggy.c):

arch/x86/boot/compressed/mkpiggy arch/x86/boot/compressed/vmlinux.bin.gz > arch/x86/boot/compressed/piggy.S

The content of piggy.S might be something like

.section ".rodata..compressed","a",@progbits
.globl z_input_len
z_input_len = 12681980
.globl z_output_len
z_output_len = 43473728
.globl input_data, input_data_end
input_data:
.incbin "arch/x86/boot/compressed/vmlinux.bin.gz"
input_data_end:
.section ".rodata","a",@progbits
.globl input_len
input_len:
	.long 12681980
.globl output_len
output_len:
	.long 43473728

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