Introduce bootblock self-decompression

Masked ROMs are the silent killers of boot speed on devices without
memory-mapped SPI flash. They often contain awfully slow SPI drivers
(presumably bit-banged) that take hundreds of milliseconds to load our
bootblock, and every extra kilobyte of bootblock size has a hugely
disproportionate impact on boot speed. The coreboot timestamps can never
show that component, but it impacts our users all the same.

This patch tries to alleviate that issue a bit by allowing us to
compress the bootblock with LZ4, which can cut its size down to nearly
half. Of course, masked ROMs usually don't come with decompression
algorithms built in, so we need to introduce a little decompression stub
that can decompress the rest of the bootblock. This is done by creating
a new "decompressor" stage which runs before the bootblock, but includes
the compressed bootblock code in its data section. It needs to be as
small as possible to get a real benefit from this approach, which means
no device drivers, no console output, no exception handling, etc.
Besides the decompression algorithm itself we only include the timer
driver so that we can measure the boot speed impact of decompression. On
ARM and ARM64 systems, we also need to give SoC code a chance to
initialize the MMU, since running decompression without MMU is
prohibitively slow on these architectures.

This feature is implemented for ARM and ARM64 architectures for now,
although most of it is architecture-independent and it should be
relatively simple to port to other platforms where a masked ROM loads
the bootblock into SRAM. It is also supposed to be a clean starting
point from which later optimizations can hopefully cut down the
decompression stub size (currently ~4K on RK3399) a bit more.

NOTE: Bootblock compression is not for everyone. Possible side effects
include trying to run LZ4 on CPUs that come out of reset extremely
underclocked or enabling this too early in SoC bring-up and getting
frustrated trying to find issues in an undebuggable environment. Ask
your SoC vendor if bootblock compression is right for you.

Change-Id: I0dc1cad9ae7508892e477739e743cd1afb5945e8
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/26340
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

Makefile.inc

@@ -104,7 +104,7 @@ subdirs-y += util/checklist util/testing
 
 #######################################################################
 # Add source classes and their build options
-classes-y := ramstage romstage bootblock postcar smm smmstub cpu_microcode verstage
+classes-y := ramstage romstage bootblock decompressor postcar smm smmstub cpu_microcode verstage
 
 # Add dynamic classes for rmodules
 $(foreach supported_arch,$(ARCH_SUPPORTED), \
@@ -186,6 +186,7 @@ ramstage-postprocess=$$(eval DEPENDENCIES+=$$(addsuffix .d,$$(basename $(1)))) \
 	$(eval $(d)ramstage.a: $(call files-in-dir,$(d),$(filter-out %.ld,$(1))); rm -f $$@ && $(AR_ramstage) rcsT $$@ $$^ ) \
 	$(eval ramstage-objs:=$(d)ramstage.a $(filter-out $(filter-out %.ld, $(call files-in-dir,$(d),$(1))),$(ramstage-objs))))
 
+decompressor-generic-ccopts += -D__PRE_RAM__ -D__DECOMPRESSOR__
 bootblock-generic-ccopts += -D__PRE_RAM__ -D__BOOTBLOCK__
 romstage-generic-ccopts += -D__PRE_RAM__ -D__ROMSTAGE__
 ramstage-generic-ccopts += -D__RAMSTAGE__
@@ -631,10 +632,30 @@ find-class = $(if $(filter $(1),$(basename $(1))),$(if $(CC_$(1)), $(1), $(call
 # the linker marked it NOBITS automatically because there are only zeroes in it.
 preserve-bss-flags := --set-section-flags .bss=load,alloc,data --set-section-flags .data=load,alloc,data
 
+ifeq ($(CONFIG_COMPRESS_BOOTBLOCK),y)
+
+$(objcbfs)/bootblock.lz4: $(objcbfs)/bootblock.elf $(objutil)/cbfstool/cbfs-compression-tool
+	@printf "    LZ4        $(subst $(obj)/,,$(@))\n"
+	$(OBJCOPY_bootblock) $(preserve-bss-flags) $< $@.tmp
+	$(OBJCOPY_bootblock) -O binary $@.tmp
+	$(objutil)/cbfstool/cbfs-compression-tool rawcompress $@.tmp $@.tmp2 lz4
+	rm -f $@.tmp
+	mv $@.tmp2 $@
+
+# Put assembled decompressor+bootblock into bootblock.raw.elf so that SoC
+# Makefiles wrapping the bootblock in a header can always key off the same file.
+$(objcbfs)/bootblock.raw.elf: $(objcbfs)/decompressor.elf
+	@printf "    OBJCOPY    $(notdir $(@))\n"
+	$(OBJCOPY_bootblock) $(preserve-bss-flags) $< $@
+
+else	# CONFIG_COMPRESS_BOOTBLOCK
+
 $(objcbfs)/bootblock.raw.elf: $(objcbfs)/bootblock.elf
 	@printf "    OBJCOPY    $(notdir $(@))\n"
 	$(OBJCOPY_bootblock) $(preserve-bss-flags) $< $@
 
+endif	# CONFIG_COMPRESS_BOOTBLOCK
+
 $(objcbfs)/bootblock.raw.bin: $(objcbfs)/bootblock.raw.elf
 	@printf "    OBJCOPY    $(notdir $(@))\n"
 	$(OBJCOPY_bootblock) -O binary $< $@
@@ -651,6 +672,7 @@ $(objcbfs)/%.elf: $(objcbfs)/%.debug
 	$(OBJCOPY_$(class)) --add-gnu-debuglink=$< $@.tmp
 	mv $@.tmp $@
 
+
 ###########################################################################
 # Build the final rom image
 ###########################################################################

src/Kconfig

@@ -146,6 +146,18 @@ config COMPRESS_PRERAM_STAGES
 	  time spent decompressing. Doesn't work for XIP stages (assume all
 	  ARCH_X86 for now) for obvious reasons.
 
+config COMPRESS_BOOTBLOCK
+	bool
+	help
+	  This option can be used to compress the bootblock with LZ4 and attach
+	  a small self-decompression stub to its front. This can drastically
+	  reduce boot time on platforms where the bootblock is loaded over a
+	  very slow connection and bootblock size trumps all other factors for
+	  speed. Since this using this option usually requires changes to the
+	  SoC memlayout and possibly extra support code, it should not be
+	  user-selectable. (There's no real point in offering this to the user
+	  anyway... if it works and saves boot time, you would always want it.)
+
 config INCLUDE_CONFIG_FILE
 	bool "Include the coreboot .config file into the ROM image"
 	# Default value set at the end of the file

src/arch/arm/Makefile.inc

@@ -44,22 +44,35 @@ endif # CONFIG_ARCH_ARM
 
 ifeq ($(CONFIG_ARCH_BOOTBLOCK_ARM),y)
 
+decompressor-y += id.S
 bootblock-y += id.S
+$(call src-to-obj,decompressor,$(dir)/id.S): $(obj)/build.h
 $(call src-to-obj,bootblock,$(dir)/id.S): $(obj)/build.h
 
+decompressor-y += boot.c
 bootblock-y += boot.c
-bootblock-y += stages.c
+decompressor-y += div0.c
-bootblock-y += eabi_compat.c
-bootblock-y += memset.S
-bootblock-y += memcpy.S
-bootblock-y += memmove.S
 bootblock-y += div0.c
+decompressor-y += eabi_compat.c
+bootblock-y += eabi_compat.c
+decompressor-y += memset.S
+bootblock-y += memset.S
+decompressor-y += memcpy.S
+bootblock-y += memcpy.S
+decompressor-y += memmove.S
+bootblock-y += memmove.S
+
 bootblock-y += clock.c
+bootblock-y += stages.c
 
 $(objcbfs)/bootblock.debug: $$(bootblock-objs)
 	@printf "    LINK       $(subst $(obj)/,,$(@))\n"
 	$(LD_bootblock) $(LDFLAGS_bootblock) -o $@ -L$(obj) -T $(call src-to-obj,bootblock,src/mainboard/$(MAINBOARDDIR)/memlayout.ld) --whole-archive --start-group $(filter-out %.ld,$(bootblock-objs)) --end-group
 
+$(objcbfs)/decompressor.debug: $$(decompressor-objs)
+	@printf "    LINK       $(subst $(obj)/,,$(@))\n"
+	$(LD_bootblock) $(LDFLAGS_bootblock) -o $@ -L$(obj) -T $(call src-to-obj,decompressor,src/mainboard/$(MAINBOARDDIR)/memlayout.ld) --whole-archive --start-group $(filter-out %.ld,$(decompressor-objs)) --end-group
+
 endif # CONFIG_ARCH_BOOTBLOCK_ARM
 
 ###############################################################################

src/arch/arm/armv7/Makefile.inc

@@ -28,18 +28,27 @@ armv7-r_asm_flags = $(armv7-r_flags) $(armv7_asm_flags)
 ###############################################################################
 
 ifeq ($(CONFIG_ARCH_BOOTBLOCK_ARMV7),y)
+decompressor-generic-ccopts += $(armv7-a_flags)
+decompressor-S-ccopts += $(armv7_asm_flags)
 bootblock-generic-ccopts += $(armv7-a_flags)
 bootblock-S-ccopts += $(armv7_asm_flags)
 
 ifneq ($(CONFIG_BOOTBLOCK_CUSTOM),y)
+decompressor-y += bootblock.S
+ifneq ($(CONFIG_COMPRESS_BOOTBLOCK),y)
 bootblock-y += bootblock.S
 endif
+endif
 
+decompressor-y += cache.c
 bootblock-y += cache.c
+decompressor-y += cpu.S
 bootblock-y += cpu.S
+decompressor-y += mmu.c
+bootblock-y += mmu.c
+
 bootblock-$(CONFIG_BOOTBLOCK_CONSOLE) += exception.c
 bootblock-$(CONFIG_BOOTBLOCK_CONSOLE) += exception_asm.S
-bootblock-y += mmu.c
 
 else ifeq ($(CONFIG_ARCH_BOOTBLOCK_ARMV7_M),y)
 bootblock-generic-ccopts += $(armv7-m_flags)

src/arch/arm/include/arch/header.ld

@@ -13,6 +13,8 @@
  * GNU General Public License for more details.
  */
 
+#include <rules.h>
+
 /* We use ELF as output format. So that we can debug the code in some form. */
 OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
 OUTPUT_ARCH(arm)
@@ -22,7 +24,7 @@ PHDRS
 	to_load PT_LOAD;
 }
 
-#ifdef __BOOTBLOCK__
+#if ENV_DECOMPRESSOR || ENV_BOOTBLOCK || ENV_RMODULE
 ENTRY(_start)
 #else
 ENTRY(stage_entry)

src/arch/arm/libgcc/Makefile.inc

@@ -19,6 +19,7 @@ libgcc_files = ashldi3.S lib1funcs.S lshrdi3.S muldi3.S ucmpdi2.S uldivmod.S
 libgcc_files += udivmoddi4.c umoddi3.c
 
 ifeq ($(CONFIG_ARCH_BOOTBLOCK_ARM),y)
+decompressor-y += $(libgcc_files)
 bootblock-y += $(libgcc_files)
 endif
 

src/arch/arm64/Makefile.inc

@@ -39,17 +39,25 @@ endif
 
 ifeq ($(CONFIG_ARCH_BOOTBLOCK_ARM64),y)
 
+decompressor-y += boot.c
+bootblock-y += boot.c
+decompressor-y += div0.c
 bootblock-y += div0.c
+decompressor-y += eabi_compat.c
+bootblock-y += eabi_compat.c
+decompressor-y += id.S
 bootblock-y += id.S
+$(call src-to-obj,decompressor,$(dir)/id.S): $(obj)/build.h
 $(call src-to-obj,bootblock,$(dir)/id.S): $(obj)/build.h
 
-bootblock-y += boot.c
-bootblock-y += eabi_compat.c
 bootblock-$(CONFIG_ARM64_USE_ARCH_TIMER) += arch_timer.c
 bootblock-y += transition.c transition_asm.S
 
+decompressor-y += memset.S
 bootblock-y += memset.S
+decompressor-y += memcpy.S
 bootblock-y += memcpy.S
+decompressor-y += memmove.S
 bootblock-y += memmove.S
 
 # Build the bootblock
@@ -58,6 +66,10 @@ $(objcbfs)/bootblock.debug: $$(bootblock-objs) $(obj)/config.h
 	@printf "    LINK       $(subst $(obj)/,,$(@))\n"
 	$(LD_bootblock) $(LDFLAGS_bootblock) -o $@ -L$(obj) --whole-archive --start-group $(filter-out %.ld,$(bootblock-objs)) --end-group -T $(call src-to-obj,bootblock,src/mainboard/$(MAINBOARDDIR)/memlayout.ld)
 
+$(objcbfs)/decompressor.debug: $$(decompressor-objs) $(obj)/config.h
+	@printf "    LINK       $(subst $(obj)/,,$(@))\n"
+	$(LD_bootblock) $(LDFLAGS_bootblock) -o $@ -L$(obj) --whole-archive --start-group $(filter-out %.ld,$(decompressor-objs)) --end-group -T $(call src-to-obj,decompressor,src/mainboard/$(MAINBOARDDIR)/memlayout.ld)
+
 endif # CONFIG_ARCH_BOOTBLOCK_ARM64
 
 ###############################################################################

src/arch/arm64/armv8/Makefile.inc

@@ -31,19 +31,27 @@ armv8_flags = -march=$(march) -I$(src)/arch/arm64/include/armv8/ -D__COREBOOT_AR
 ifeq ($(CONFIG_ARCH_BOOTBLOCK_ARMV8_64),y)
 
 ifneq ($(CONFIG_BOOTBLOCK_CUSTOM),y)
+decompressor-y += bootblock.S
+ifneq ($(CONFIG_COMPRESS_BOOTBLOCK),y)
 bootblock-y += bootblock.S
 endif
-bootblock-y += cache.c
+endif
+decompressor-y += cpu.S
 bootblock-y += cpu.S
+decompressor-y += cache.c
+bootblock-y += cache.c
+decompressor-y += mmu.c
 bootblock-y += mmu.c
 
 bootblock-$(CONFIG_BOOTBLOCK_CONSOLE) += exception.c
 
+decompressor-generic-ccopts += $(armv8_flags)
 bootblock-generic-ccopts += $(armv8_flags)
 
 # Required to access unaligned timestamp struct members before MMU is active
 # (TODO: Maybe use explicit unaligned accesses in timestamp code instead, or
 # evaluate redesigning timestamp data structures to avoid misaligned members.)
+decompressor-c-ccopts += -mstrict-align
 bootblock-c-ccopts += -mstrict-align
 
 endif

src/arch/arm64/armv8/lib/Makefile.inc

@@ -18,6 +18,7 @@
 lib_access = pstate.c sysctrl.c cache.c tlb.c clock.c
 
 ifeq ($(CONFIG_ARCH_BOOTBLOCK_ARMV8_64),y)
+decompressor-y += $(lib_access)
 bootblock-y += $(lib_access)
 endif
 

src/arch/arm64/include/arch/header.ld

@@ -24,7 +24,7 @@ PHDRS
 	to_load PT_LOAD;
 }
 
-#if ENV_BOOTBLOCK ||  ENV_RMODULE
+#if ENV_DECOMPRESSOR || ENV_BOOTBLOCK || ENV_RMODULE
 ENTRY(_start)
 #else
 ENTRY(stage_entry)

src/commonlib/Makefile.inc

@@ -30,6 +30,7 @@ ramstage-y += cbfs.c
 smm-y += cbfs.c
 postcar-y += cbfs.c
 
+decompressor-y += lz4_wrapper.c
 bootblock-y += lz4_wrapper.c
 verstage-y += lz4_wrapper.c
 romstage-y += lz4_wrapper.c

src/console/Makefile.inc

@@ -32,3 +32,5 @@ bootblock-y += vtxprintf.c vsprintf.c
 bootblock-$(CONFIG_BOOTBLOCK_CONSOLE) += init.c console.c
 bootblock-y += post.c
 bootblock-y += die.c
+
+decompressor-y += die.c

src/include/bootblock_common.h

@@ -26,6 +26,7 @@
  * The 'early' variants are called prior to console initialization. Also, the
  * SoC functions are called prior to the mainboard fucntions.
  */
+void decompressor_soc_init(void);
 void bootblock_mainboard_early_init(void);
 void bootblock_mainboard_init(void);
 void bootblock_soc_early_init(void);
@@ -47,4 +48,11 @@ asmlinkage void bootblock_c_entry(uint64_t base_timestamp);
 asmlinkage void bootblock_main_with_timestamp(uint64_t base_timestamp,
 	struct timestamp_entry *timestamps, size_t num_timestamps);
 
+/* This is the argument structure passed from decompressor to bootblock. */
+struct bootblock_arg {
+	uint64_t base_timestamp;
+	uint32_t num_timestamps;
+	struct timestamp_entry timestamps[];
+};
+
 #endif	/* __BOOTBLOCK_COMMON_H */

src/include/memlayout.h

@@ -102,6 +102,26 @@
 #endif
 
 /* Careful: 'INCLUDE <filename>' must always be at the end of the output line */
+#if ENV_DECOMPRESSOR
+	#define DECOMPRESSOR(addr, sz) \
+		SYMBOL(decompressor, addr) \
+		_edecompressor = _decompressor + sz; \
+		_ = ASSERT(_eprogram - _program <= sz, \
+			STR(decompressor exceeded its allotted size! (sz))); \
+		INCLUDE "decompressor/lib/program.ld"
+
+	#define OVERLAP_DECOMPRESSOR_ROMSTAGE(addr, sz) DECOMPRESSOR(addr, sz)
+	#define OVERLAP_DECOMPRESSOR_VERSTAGE_ROMSTAGE(addr, sz) \
+		DECOMPRESSOR(addr, sz)
+#else
+	#define DECOMPRESSOR(addr, sz) \
+		REGION(decompressor, addr, sz, 1)
+
+	#define OVERLAP_DECOMPRESSOR_ROMSTAGE(addr, sz) ROMSTAGE(addr, sz)
+	#define OVERLAP_DECOMPRESSOR_VERSTAGE_ROMSTAGE(addr, sz) \
+		OVERLAP_VERSTAGE_ROMSTAGE(addr, sz)
+#endif
+
 #if ENV_BOOTBLOCK
 	#define BOOTBLOCK(addr, sz) \
 		SYMBOL(bootblock, addr) \

src/include/program_loading.h

@@ -28,6 +28,7 @@ enum {
 
 enum prog_type {
 	PROG_UNKNOWN,
+	PROG_BOOTBLOCK,
 	PROG_VERSTAGE,
 	PROG_ROMSTAGE,
 	PROG_RAMSTAGE,

src/include/rules.h

@@ -19,7 +19,20 @@
  * romstage, ramstage or SMM.
  */
 
-#if defined(__BOOTBLOCK__)
+#if defined(__DECOMPRESSOR__)
+#define ENV_DECOMPRESSOR 1
+#define ENV_BOOTBLOCK 0
+#define ENV_ROMSTAGE 0
+#define ENV_RAMSTAGE 0
+#define ENV_SMM 0
+#define ENV_VERSTAGE 0
+#define ENV_RMODULE 0
+#define ENV_POSTCAR 0
+#define ENV_LIBAGESA 0
+#define ENV_STRING "decompressor"
+
+#elif defined(__BOOTBLOCK__)
+#define ENV_DECOMPRESSOR 0
 #define ENV_BOOTBLOCK 1
 #define ENV_ROMSTAGE 0
 #define ENV_RAMSTAGE 0
@@ -31,6 +44,7 @@
 #define ENV_STRING "bootblock"
 
 #elif defined(__ROMSTAGE__)
+#define ENV_DECOMPRESSOR 0
 #define ENV_BOOTBLOCK 0
 #define ENV_ROMSTAGE 1
 #define ENV_RAMSTAGE 0
@@ -42,6 +56,7 @@
 #define ENV_STRING "romstage"
 
 #elif defined(__SMM__)
+#define ENV_DECOMPRESSOR 0
 #define ENV_BOOTBLOCK 0
 #define ENV_ROMSTAGE 0
 #define ENV_RAMSTAGE 0
@@ -53,6 +68,7 @@
 #define ENV_STRING "smm"
 
 #elif defined(__VERSTAGE__)
+#define ENV_DECOMPRESSOR 0
 #define ENV_BOOTBLOCK 0
 #define ENV_ROMSTAGE 0
 #define ENV_RAMSTAGE 0
@@ -64,6 +80,7 @@
 #define ENV_STRING "verstage"
 
 #elif defined(__RAMSTAGE__)
+#define ENV_DECOMPRESSOR 0
 #define ENV_BOOTBLOCK 0
 #define ENV_ROMSTAGE 0
 #define ENV_RAMSTAGE 1
@@ -75,6 +92,7 @@
 #define ENV_STRING "ramstage"
 
 #elif defined(__RMODULE__)
+#define ENV_DECOMPRESSOR 0
 #define ENV_BOOTBLOCK 0
 #define ENV_ROMSTAGE 0
 #define ENV_RAMSTAGE 0
@@ -86,6 +104,7 @@
 #define ENV_STRING "rmodule"
 
 #elif defined(__POSTCAR__)
+#define ENV_DECOMPRESSOR 0
 #define ENV_BOOTBLOCK 0
 #define ENV_ROMSTAGE 0
 #define ENV_RAMSTAGE 0
@@ -97,6 +116,7 @@
 #define ENV_STRING "postcar"
 
 #elif defined(__LIBAGESA__)
+#define ENV_DECOMPRESSOR 0
 #define ENV_BOOTBLOCK 0
 #define ENV_ROMSTAGE 0
 #define ENV_RAMSTAGE 0
@@ -112,6 +132,7 @@
  * Default case of nothing set for random blob generation using
  * create_class_compiler that isn't bound to a stage.
  */
+#define ENV_DECOMPRESSOR 0
 #define ENV_BOOTBLOCK 0
 #define ENV_ROMSTAGE 0
 #define ENV_RAMSTAGE 0

src/include/symbols.h

@@ -68,6 +68,10 @@ extern u8 _eprogram[];
 
 /* _<stage>_size is always the maximum amount allocated in memlayout, whereas
  * _program_size gives the actual memory footprint *used* by current stage. */
+extern u8 _decompressor[];
+extern u8 _edecompressor[];
+#define _decompressor_size (_edecompressor - _decompressor)
+
 extern u8 _bootblock[];
 extern u8 _ebootblock[];
 #define _bootblock_size (_ebootblock - _bootblock)

src/lib/Makefile.inc

@@ -19,6 +19,19 @@ ramstage-y += ubsan.c
 CFLAGS_ramstage += -fsanitize=undefined
 endif
 
+decompressor-y += decompressor.c
+$(call src-to-obj,decompressor,$(dir)/decompressor.c): $(objcbfs)/bootblock.lz4
+$(call src-to-obj,decompressor,$(dir)/decompressor.c): CCACHE_EXTRAFILES=$(objcbfs)/bootblock.lz4
+# Must reset CCACHE_EXTRAFILES or make applies it transitively to dependencies.
+$(objcbfs)/bootblock.lz4: CCACHE_EXTRAFILES=
+
+decompressor-y += delay.c
+decompressor-$(CONFIG_GENERIC_GPIO_LIB) += gpio.c
+decompressor-y += memchr.c
+decompressor-y += memcmp.c
+decompressor-y += prog_ops.c
+decompressor-$(CONFIG_COLLECT_TIMESTAMPS) += timestamp.c
+
 ifneq ($(CONFIG_BOOTBLOCK_CUSTOM),y)
 bootblock-y += bootblock.c
 endif
@@ -216,11 +229,13 @@ romstage-y += bootmode.c
 ramstage-y += bootmode.c
 verstage-y += bootmode.c
 
+decompressor-y += halt.c
 bootblock-y += halt.c
 romstage-y += halt.c
 ramstage-y += halt.c
 smm-y += halt.c
 
+decompressor-y += reset.c
 bootblock-y += reset.c
 verstage-y += reset.c
 romstage-y += reset.c
@@ -248,6 +263,7 @@ postcar-$(CONFIG_GENERIC_UDELAY) += timer.c
 # Use program.ld for all the platforms which use C fo the bootblock.
 bootblock-$(CONFIG_C_ENVIRONMENT_BOOTBLOCK) += program.ld
 
+decompressor-y += program.ld
 postcar-y += program.ld
 romstage-y += program.ld
 ramstage-y += program.ld

src/lib/bootblock.c

@@ -70,3 +70,20 @@ void main(void)
 
 	bootblock_main_with_timestamp(base_timestamp, NULL, 0);
 }
+
+#if IS_ENABLED(CONFIG_COMPRESS_BOOTBLOCK)
+/*
+ * This is the bootblock entry point when it is run after a decompressor stage.
+ * For non-decompressor builds, _start is generally defined in architecture-
+ * specific assembly code. In decompressor builds that architecture
+ * initialization code already ran in the decompressor, so the bootblock can
+ * start straight into common code with a C environment.
+ */
+void _start(struct bootblock_arg *arg);
+void _start(struct bootblock_arg *arg)
+{
+	bootblock_main_with_timestamp(arg->base_timestamp, arg->timestamps,
+				      arg->num_timestamps);
+}
+
+#endif

src/lib/decompressor.c

@@ -0,0 +1,70 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright 2018 Google Inc.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; version 2 of
+ * the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <bootblock_common.h>
+#include <commonlib/compression.h>
+#include <delay.h>
+#include <program_loading.h>
+#include <symbols.h>
+
+extern u8 compressed_bootblock[];
+asm (
+	".pushsection .data.compressed_bootblock,\"a\",@progbits\n\t"
+	".type compressed_bootblock, %object\n\t"
+	".balign 8\n"
+	"compressed_bootblock:\n\t"
+	".incbin \"" __BUILD_DIR__ "/cbfs/" CONFIG_CBFS_PREFIX "/bootblock.lz4\"\n\t"
+	".size compressed_bootblock, . - compressed_bootblock\n\t"
+	".popsection\n\t"
+);
+
+struct bootblock_arg arg = {
+	.base_timestamp = 0,
+	.num_timestamps = 2,
+	.timestamps = {
+		{ .entry_id = TS_START_ULZ4F },
+		{ .entry_id = TS_END_ULZ4F },
+	},
+};
+
+struct prog prog_bootblock = {
+	.type = PROG_BOOTBLOCK,
+	.entry = (void *)_bootblock,
+	.arg = &arg,
+};
+
+__weak void decompressor_soc_init(void) { /* no-op */ }
+
+void main(void)
+{
+	init_timer();
+
+	if (IS_ENABLED(CONFIG_COLLECT_TIMESTAMPS))
+		arg.base_timestamp = timestamp_get();
+
+	decompressor_soc_init();
+
+	if (IS_ENABLED(CONFIG_COLLECT_TIMESTAMPS))
+		arg.timestamps[0].entry_stamp = timestamp_get();
+
+	size_t out_size = ulz4f(compressed_bootblock, _bootblock);
+	prog_segment_loaded((uintptr_t)_bootblock, out_size, SEG_FINAL);
+
+	if (IS_ENABLED(CONFIG_COLLECT_TIMESTAMPS))
+		arg.timestamps[1].entry_stamp = timestamp_get();
+
+	prog_run(&prog_bootblock);
+}

src/lib/program.ld

@@ -34,7 +34,9 @@
 	*(.rom.data);
 	*(.text._start);
 	*(.text.stage_entry);
-#if ENV_BOOTBLOCK && !(IS_ENABLED(CONFIG_ARCH_BOOTBLOCK_X86_32) || \
+#if (ENV_DECOMPRESSOR || ENV_BOOTBLOCK && \
+		!IS_ENABLED(CONFIG_COMPRESS_BOOTBLOCK)) && \
+    !(IS_ENABLED(CONFIG_ARCH_BOOTBLOCK_X86_32) || \
       IS_ENABLED(CONFIG_ARCH_BOOTBLOCK_X86_64))
 	KEEP(*(.id));
 #endif

toolchain.inc

@@ -47,7 +47,8 @@ HOSTCXX:=CCC_CXX="$(HOSTCXX)" $(CXX)
 ROMCC=CCC_CC="$(ROMCC_BIN)" $(CC)
 endif
 
-COREBOOT_STANDARD_STAGES := bootblock verstage romstage ramstage
+COREBOOT_STANDARD_STAGES := decompressor bootblock verstage romstage ramstage
+MAP-decompressor := bootblock
 
 ARCHDIR-i386	:= x86
 ARCHDIR-x86_32	:= x86