[LINUX] Read a little more arch / arm / boot / compressed / Makefile

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/compressed/Makefile?h=master

Read the contents of the Makefile. Omit the fdt part that you are not interested in.

TEXT area settings, etc.

arch/arm/boot/compressed/Makefile


# SPDX-License-Identifier: GPL-2.0
#
# linux/arch/arm/boot/compressed/Makefile
#
# create a compressed vmlinuz image from the original vmlinux
#

OBJS		=
AFLAGS_head.o += -DTEXT_OFFSET=$(TEXT_OFFSET)

It means to add the option of TEXT_OFFSET when creating head.o.

TEXT_OFFSET $ (TEXT_OFFSET) is defined in arch / arm / Makefile.

arch/arm/Makefile


# Text offset. This list is sorted numerically by address in order to
# provide a means to avoid/resolve conflicts in multi-arch kernels.
textofs-y	:= 0x00008000
# We don't want the htc bootloader to corrupt kernel during resume
textofs-$(CONFIG_PM_H1940)      := 0x00108000
# SA1111 DMA bug: we don't want the kernel to live in precious DMA-able memory
ifeq ($(CONFIG_ARCH_SA1100),y)
textofs-$(CONFIG_SA1111) := 0x00208000
endif
textofs-$(CONFIG_ARCH_IPQ40XX) := 0x00208000
textofs-$(CONFIG_ARCH_MSM8X60) := 0x00208000
textofs-$(CONFIG_ARCH_MSM8960) := 0x00208000
textofs-$(CONFIG_ARCH_MESON) := 0x00208000
textofs-$(CONFIG_ARCH_AXXIA) := 0x00308000

(Omitted)

TEXT_OFFSET := $(textofs-y)

Code that actually processes as a kernel (head. * / Misc. * / Decompress. *)

arch/arm/boot/compressed/Makefile


HEAD	= head.o
OBJS	+= misc.o decompress.o

head.S This is the logic of the compressed Linux Kernel expansion section itself.

Do various things, but call decompress_kernel.

arch/arm/boot/compressed/head.S


/*
 * The C runtime environment should now be setup sufficiently.
 * Set up some pointers, and start decompressing.
 *   r4  = kernel execution address
 *   r7  = architecture ID
 *   r8  = atags pointer
 */
		mov	r0, r4
		mov	r1, sp			@ malloc space above stack
		add	r2, sp, #0x10000	@ 64k max
		mov	r3, r7
		bl	decompress_kernel

misc.S The main body of decompress_kernel () is described.

Actually, do_decompress () is called from this.

arch/arm/boot/compressed/misc.c


void
decompress_kernel(unsigned long output_start, unsigned long free_mem_ptr_p,
		unsigned long free_mem_ptr_end_p,
		int arch_id)
{
	int ret;

	output_data		= (unsigned char *)output_start;
	free_mem_ptr		= free_mem_ptr_p;
	free_mem_end_ptr	= free_mem_ptr_end_p;
	__machine_arch_type	= arch_id;

	arch_decomp_setup();

	putstr("Uncompressing Linux...");
	ret = do_decompress(input_data, input_data_end - input_data,
			    output_data, error);
	if (ret)
		error("decompressor returned an error");
	else
		putstr(" done, booting the kernel.\n");
}

decompress.S

The part that calls __decompress () of each compression module to decompress it.

arch/arm/boot/compressed/decompress.c


#ifdef CONFIG_KERNEL_GZIP
#include "../../../../lib/decompress_inflate.c"
#endif

#ifdef CONFIG_KERNEL_LZO
#include "../../../../lib/decompress_unlzo.c"
#endif

#ifdef CONFIG_KERNEL_LZMA
#include "../../../../lib/decompress_unlzma.c"
#endif

#ifdef CONFIG_KERNEL_XZ
#define memmove memmove
#define memcpy memcpy
#include "../../../../lib/decompress_unxz.c"
#endif

#ifdef CONFIG_KERNEL_LZ4
#include "../../../../lib/decompress_unlz4.c"
#endif

int do_decompress(u8 *input, int len, u8 *output, void (*error)(char *x))
{
	return __decompress(input, len, NULL, NULL, output, 0, NULL, error);
}

For example, for lz4:

lib/decompress_unlz4.c


#ifdef PREBOOT
STATIC int INIT __decompress(unsigned char *buf, long in_len,
                  long (*fill)(void*, unsigned long),
                  long (*flush)(void*, unsigned long),
                  unsigned char *output, long out_len,
                  long *posp,
                  void (*error)(char *x)
    )
{
    return unlz4(buf, in_len - 4, fill, flush, output, posp, error);
}
#endif

Character output for debug

arch/arm/boot/compressed/Makefile


ifeq ($(CONFIG_DEBUG_UNCOMPRESS),y)
OBJS	+= debug.o
endif
FONTC	= $(srctree)/lib/fonts/font_acorn_8x8.c

I think font_acorn_8x8.c isn't used except for acorn ...

DEBUG_UNCOMPRESS

DEBUG_UNCOMPRESS is defined in KConfig.debug.

This option concerns the output of the decompressor on a multiplatform kernel. Usually, decompressor is not good for multiplatform kernels. Because I don't know where to send the decompressor output.

Once this option is set, it will be reused by the DEBUG_LL output means.

So you can debug it.

arch/arm/Kconfig.debug


config DEBUG_UNCOMPRESS
	bool "Enable decompressor debugging via DEBUG_LL output"
	depends on ARCH_MULTIPLATFORM || PLAT_SAMSUNG || ARM_SINGLE_ARMV7M
	depends on DEBUG_LL && !DEBUG_OMAP2PLUS_UART && \
		     (!DEBUG_TEGRA_UART || !ZBOOT_ROM) && \
		     !DEBUG_BRCMSTB_UART
	help
	  This option influences the normal decompressor output for
	  multiplatform kernels.  Normally, multiplatform kernels disable
	  decompressor output because it is not possible to know where to
	  send the decompressor output.

	  When this option is set, the selected DEBUG_LL output method
	  will be re-used for normal decompressor output on multiplatform
	  kernels.

debug.S

debug.s is used for the implementation of putc (). If CONFIG_DEBUG_SEMIHOSTING is disabled, adduart / waituart / senduart / busyuart will output the characters to the console.

arm/boot/compressed/debug.S


/* SPDX-License-Identifier: GPL-2.0 */
#include <linux/linkage.h>
#include <asm/assembler.h>

#ifndef CONFIG_DEBUG_SEMIHOSTING

#include CONFIG_DEBUG_LL_INCLUDE

ENTRY(putc)
	addruart r1, r2, r3
	waituart r3, r1
	senduart r0, r1
	busyuart r3, r1
	mov	 pc, lr
ENDPROC(putc)

#else
(Omitted)

string library

string.c is a subset of memcpu / memmove / strlen / strnlen. Estimated to be built in so that the decompressor can move independently when it moves.

arch/arm/boot/compressed/Makefile


# string library code (-Os is enforced to keep it much smaller)
OBJS		+= string.o
CFLAGS_string.o	:= -Os

string.c

The content is an implementation of a simplified version of the function defined in string.h.

arch/arm/boot/compressed/string.c


void *memcpy(void *__dest, __const void *__src, size_t __n)
{
	int i = 0;
	unsigned char *d = (unsigned char *)__dest, *s = (unsigned char *)__src;

	for (i = __n >> 3; i > 0; i--) {
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
	}

	if (__n & 1 << 2) {
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
	}

	if (__n & 1 << 1) {
		*d++ = *s++;
		*d++ = *s++;
	}

	if (__n & 1)
		*d++ = *s++;

	return __dest;
}

VIRT_EXT

arch/arm/boot/compressed/Makefile


ifeq ($(CONFIG_ARM_VIRT_EXT),y)
OBJS		+= hyp-stub.o
endif

ARM_VIRT_EXT

arch/arm/mm/Kconfig


config ARM_VIRT_EXT
    bool
    default y if CPU_V7
    help
      Enable the kernel to make use of the ARM Virtualization
      Extensions to install hypervisors without run-time firmware
      assistance.

      A compliant bootloader is required in order to make maximum
      use of this feature.  Refer to Documentation/arm/booting.rst for
      details.

GCOV/KCOV

The debugging function has been disabled.

arch/arm/boot/compressed/Makefile


GCOV_PROFILE		:= n

# Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
KCOV_INSTRUMENT		:= n

Machine-dependent part

This area is model-dependent, so it is omitted.

arch/arm/boot/compressed/Makefile


#
# Architecture dependencies
#
ifeq ($(CONFIG_ARCH_ACORN),y)
OBJS		+= ll_char_wr.o font.o
endif

<Omitted>

Address specification (ZTEXTADDR / ZBSSADDR)

--The decompressor implementation is PIC (address independent implementation). --When running Decompressor on RAM, do not specify ZTEXTADDR. --If you want to run Decompressor with ROM / Flash, you need to specify it.

arch/arm/boot/compressed/Makefile


#
# We now have a PIC decompressor implementation.  Decompressors running
# from RAM should not define ZTEXTADDR.  Decompressors running directly
# from ROM or Flash must define ZTEXTADDR (preferably via the config)
# FIXME: Previous assignment to ztextaddr-y is lost here. See SHARK
ifeq ($(CONFIG_ZBOOT_ROM),y)
ZTEXTADDR	:= $(CONFIG_ZBOOT_ROM_TEXT)
ZBSSADDR	:= $(CONFIG_ZBOOT_ROM_BSS)
else
ZTEXTADDR	:= 0
ZBSSADDR	:= ALIGN(8)
endif

CPPFLAGS_vmlinux.lds := -DTEXT_START="$(ZTEXTADDR)" -DBSS_START="$(ZBSSADDR)"

Confirmation of compression method

Specify the compression format specified by KConfig.

arch/arm/boot/compressed/Makefile



compress-$(CONFIG_KERNEL_GZIP) = gzip
compress-$(CONFIG_KERNEL_LZO)  = lzo
compress-$(CONFIG_KERNEL_LZMA) = lzma
compress-$(CONFIG_KERNEL_XZ)   = xzkern
compress-$(CONFIG_KERNEL_LZ4)  = lz4

fdt part (omitted)

arch/arm/boot/compressed/Makefile



# Borrowed libfdt files for the ATAG compatibility mode
<Omitted>

Target / clean-files settings for Make

arch/arm/boot/compressed/Makefile


targets       := vmlinux vmlinux.lds piggy_data piggy.o \
		 lib1funcs.o ashldi3.o bswapsdi2.o \
		 head.o $(OBJS)

clean-files += piggy_data lib1funcs.S ashldi3.S bswapsdi2.S \
		$(libfdt) $(libfdt_hdrs) hyp-stub.S

KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING

ifeq ($(CONFIG_FUNCTION_TRACER),y)
ORIG_CFLAGS := $(KBUILD_CFLAGS)
KBUILD_CFLAGS = $(subst -pg, , $(ORIG_CFLAGS))
endif

fdt part 2 (omitted)

It seems that it is still early to use stack-protector-strong.

arch/arm/boot/compressed/Makefile


# -fstack-protector-strong triggers protection checks in this code,
# but it is being used too early to link to meaningful stack_chk logic.
nossp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
CFLAGS_atags_to_fdt.o := $(nossp-flags-y)
<Omitted>

BSS size specification.

It seems that it is calculated using between \ _ \ _ bss_start and \ _ \ _ bss_stop. That is communicated as an option to the Linker.

arch/arm/boot/compressed/Makefile


# Supply kernel BSS size to the decompressor via a linker symbol.
KBSS_SZ = $(shell echo $$(($$($(NM) $(obj)/../../../../vmlinux | \
		sed -n -e 's/^\([^ ]*\) [AB] __bss_start$$/-0x\1/p' \
		       -e 's/^\([^ ]*\) [AB] __bss_stop$$/+0x\1/p') )) )
LDFLAGS_vmlinux = --defsym _kernel_bss_size=$(KBSS_SZ)
# Supply ZRELADDR to the decompressor via a linker symbol.
ifneq ($(CONFIG_AUTO_ZRELADDR),y)
LDFLAGS_vmlinux += --defsym zreladdr=$(ZRELADDR)
endif

Other settings when linking vmlinux

--Big Endian support --No unresolved references --Temporary removal of local symbols --- The T option is for the linker script, isn't it?

arch/arm/boot/compressed/Makefile


ifeq ($(CONFIG_CPU_ENDIAN_BE8),y)
LDFLAGS_vmlinux += --be8
endif
# Report unresolved symbol references
LDFLAGS_vmlinux += --no-undefined
# Delete all temporary local symbols
LDFLAGS_vmlinux += -X
# Next argument is a linker script
LDFLAGS_vmlinux += -T

Correspondence for non-existent instructions.

Deployment of code prepared to mess with non-existent functions.

arch/arm/boot/compressed/Makefile


# For __aeabi_uidivmod
lib1funcs = $(obj)/lib1funcs.o

$(obj)/lib1funcs.S: $(srctree)/arch/$(SRCARCH)/lib/lib1funcs.S
	$(call cmd,shipped)

# For __aeabi_llsl
ashldi3 = $(obj)/ashldi3.o

$(obj)/ashldi3.S: $(srctree)/arch/$(SRCARCH)/lib/ashldi3.S
	$(call cmd,shipped)

# For __bswapsi2, __bswapdi2
bswapsdi2 = $(obj)/bswapsdi2.o

$(obj)/bswapsdi2.S: $(srctree)/arch/$(SRCARCH)/lib/bswapsdi2.S
	$(call cmd,shipped)

lib1funcs.S It seems to be a division optimization routine.

https://gcc.gnu.org/onlinedocs/gccint/Integer-library-routines.html

The following functions etc. are included.

Runtime Function: int __divsi3 (int a, int b) Runtime Function: long __divdi3 (long a, long b) Runtime Function: long long __divti3 (long long a, long long b)   These functions return the quotient of the signed division of a and b.

arch/arm/lib/lib1funcs.S


/*
 * linux/arch/arm/lib/lib1funcs.S: Optimized ARM division routines
 *
 * Author: Nicolas Pitre <[email protected]>
 *   - contributed to gcc-3.4 on Sep 30, 2003
 *   - adapted for the Linux kernel on Oct 2, 2003
 */

ashldi3.S/bswapsdi2.S https://gcc.gnu.org/onlinedocs/gccint/Integer-library-routines.html

There is a description of what the function is around here.

Runtime Function: int __ashlsi3 (int a, int b) Runtime Function: long __ashldi3 (long a, int b) Runtime Function: long long __ashlti3 (long long a, int b)   These functions return the result of shifting a left by b bits.

Runtime Function: int32_t __bswapsi2 (int32_t a) Runtime Function: int64_t __bswapdi2 (int64_t a)   These functions return the a byteswapped.

Symbol check.

"The following symbols must not be in the local / private scope," he said.

arch/arm/boot/compressed/Makefile



# We need to prevent any GOTOFF relocs being used with references
# to symbols in the .bss section since we cannot relocate them
# independently from the rest at run time.  This can be achieved by
# ensuring that no private .bss symbols exist, as global symbols
# always have a GOT entry which is what we need.
# The .data section is already discarded by the linker script so no need
# to bother about it here.
check_for_bad_syms = \
bad_syms=$$($(NM) [email protected] | sed -n 's/^.\{8\} [bc] \(.*\)/\1/p') && \
[ -z "$$bad_syms" ] || \
  ( echo "following symbols must have non local/private scope:" >&2; \
    echo "$$bad_syms" >&2; false )

ZRELADDR related check

If ZRELADDR is not set and AUTO_ZRELADDR is not set, will I get angry?

arch/arm/boot/compressed/Makefile


check_for_multiple_zreladdr = \
if [ $(words $(ZRELADDR)) -gt 1 -a "$(CONFIG_AUTO_ZRELADDR)" = "" ]; then \
	echo 'multiple zreladdrs: $(ZRELADDR)'; \
	echo 'This needs CONFIG_AUTO_ZRELADDR to be set'; \
	false; \
fi

EFI compatible

(Omitted without interest)

arch/arm/boot/compressed/Makefile


efi-obj-$(CONFIG_EFI_STUB) := $(objtree)/drivers/firmware/efi/libstub/lib.a

How to make vmlinux! !! (This is the final line)

arch/arm/boot/compressed/Makefile


$(obj)/vmlinux: $(obj)/vmlinux.lds $(obj)/$(HEAD) $(obj)/piggy.o \
		$(addprefix $(obj)/, $(OBJS)) $(lib1funcs) $(ashldi3) \
		$(bswapsdi2) $(efi-obj-y) FORCE
	@$(check_for_multiple_zreladdr)
	$(call if_changed,ld)
	@$(check_for_bad_syms)

Compress Image

compress-y contains the compression program specified in the form compress- $ (CONFIG_KERNEL_XXXX) = CMD. Use this to convert Image to piggy_data

arch/arm/boot/compressed/Makefile



$(obj)/piggy_data: $(obj)/../Image FORCE
	$(call if_changed,$(compress-y))

$(obj)/piggy.o: $(obj)/piggy_data

piggy.S

I have imported piggy_data as binary data.

arch/arm/boot/compressed/piggy.S


/* SPDX-License-Identifier: GPL-2.0 */
	.section .piggydata, "a"
	.globl	input_data
input_data:
	.incbin	"arch/arm/boot/compressed/piggy_data"
	.globl	input_data_end
input_data_end:

After that, specify various options

arch/arm/boot/compressed/Makefile



CFLAGS_font.o := -Dstatic=

$(obj)/font.c: $(FONTC)
	$(call cmd,shipped)

AFLAGS_hyp-stub.o := -Wa,-march=armv7-a

$(obj)/hyp-stub.S: $(srctree)/arch/$(SRCARCH)/kernel/hyp-stub.S
	$(call cmd,shipped)

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