![Steven Rostedt](/assets/img/avatar_default.png)
This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
380 lines
11 KiB
Makefile
380 lines
11 KiB
Makefile
# ==========================================================================
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# Building
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# ==========================================================================
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src := $(obj)
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PHONY := __build
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__build:
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# Init all relevant variables used in kbuild files so
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# 1) they have correct type
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# 2) they do not inherit any value from the environment
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obj-y :=
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obj-m :=
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lib-y :=
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lib-m :=
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always :=
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targets :=
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subdir-y :=
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subdir-m :=
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EXTRA_AFLAGS :=
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EXTRA_CFLAGS :=
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EXTRA_CPPFLAGS :=
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EXTRA_LDFLAGS :=
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asflags-y :=
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ccflags-y :=
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cppflags-y :=
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ldflags-y :=
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# Read auto.conf if it exists, otherwise ignore
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-include include/config/auto.conf
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include scripts/Kbuild.include
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# For backward compatibility check that these variables do not change
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save-cflags := $(CFLAGS)
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# The filename Kbuild has precedence over Makefile
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kbuild-dir := $(if $(filter /%,$(src)),$(src),$(srctree)/$(src))
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kbuild-file := $(if $(wildcard $(kbuild-dir)/Kbuild),$(kbuild-dir)/Kbuild,$(kbuild-dir)/Makefile)
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include $(kbuild-file)
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# If the save-* variables changed error out
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ifeq ($(KBUILD_NOPEDANTIC),)
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ifneq ("$(save-cflags)","$(CFLAGS)")
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$(error CFLAGS was changed in "$(kbuild-file)". Fix it to use EXTRA_CFLAGS)
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endif
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endif
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include scripts/Makefile.lib
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ifdef host-progs
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ifneq ($(hostprogs-y),$(host-progs))
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$(warning kbuild: $(obj)/Makefile - Usage of host-progs is deprecated. Please replace with hostprogs-y!)
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hostprogs-y += $(host-progs)
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endif
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endif
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# Do not include host rules unless needed
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ifneq ($(hostprogs-y)$(hostprogs-m),)
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include scripts/Makefile.host
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endif
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ifneq ($(KBUILD_SRC),)
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# Create output directory if not already present
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_dummy := $(shell [ -d $(obj) ] || mkdir -p $(obj))
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# Create directories for object files if directory does not exist
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# Needed when obj-y := dir/file.o syntax is used
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_dummy := $(foreach d,$(obj-dirs), $(shell [ -d $(d) ] || mkdir -p $(d)))
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endif
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ifndef obj
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$(warning kbuild: Makefile.build is included improperly)
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endif
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# ===========================================================================
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ifneq ($(strip $(lib-y) $(lib-m) $(lib-n) $(lib-)),)
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lib-target := $(obj)/lib.a
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endif
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ifneq ($(strip $(obj-y) $(obj-m) $(obj-n) $(obj-) $(lib-target)),)
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builtin-target := $(obj)/built-in.o
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endif
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modorder-target := $(obj)/modules.order
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# We keep a list of all modules in $(MODVERDIR)
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__build: $(if $(KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y)) \
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$(if $(KBUILD_MODULES),$(obj-m) $(modorder-target)) \
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$(subdir-ym) $(always)
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@:
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# Linus' kernel sanity checking tool
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ifneq ($(KBUILD_CHECKSRC),0)
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ifeq ($(KBUILD_CHECKSRC),2)
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quiet_cmd_force_checksrc = CHECK $<
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cmd_force_checksrc = $(CHECK) $(CHECKFLAGS) $(c_flags) $< ;
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else
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quiet_cmd_checksrc = CHECK $<
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cmd_checksrc = $(CHECK) $(CHECKFLAGS) $(c_flags) $< ;
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endif
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endif
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# Do section mismatch analysis for each module/built-in.o
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ifdef CONFIG_DEBUG_SECTION_MISMATCH
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cmd_secanalysis = ; scripts/mod/modpost $@
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endif
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# Compile C sources (.c)
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# ---------------------------------------------------------------------------
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# Default is built-in, unless we know otherwise
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modkern_cflags := $(CFLAGS_KERNEL)
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quiet_modtag := $(empty) $(empty)
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$(real-objs-m) : modkern_cflags := $(CFLAGS_MODULE)
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$(real-objs-m:.o=.i) : modkern_cflags := $(CFLAGS_MODULE)
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$(real-objs-m:.o=.s) : modkern_cflags := $(CFLAGS_MODULE)
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$(real-objs-m:.o=.lst): modkern_cflags := $(CFLAGS_MODULE)
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$(real-objs-m) : quiet_modtag := [M]
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$(real-objs-m:.o=.i) : quiet_modtag := [M]
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$(real-objs-m:.o=.s) : quiet_modtag := [M]
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$(real-objs-m:.o=.lst): quiet_modtag := [M]
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$(obj-m) : quiet_modtag := [M]
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# Default for not multi-part modules
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modname = $(basetarget)
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$(multi-objs-m) : modname = $(modname-multi)
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$(multi-objs-m:.o=.i) : modname = $(modname-multi)
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$(multi-objs-m:.o=.s) : modname = $(modname-multi)
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$(multi-objs-m:.o=.lst) : modname = $(modname-multi)
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$(multi-objs-y) : modname = $(modname-multi)
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$(multi-objs-y:.o=.i) : modname = $(modname-multi)
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$(multi-objs-y:.o=.s) : modname = $(modname-multi)
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$(multi-objs-y:.o=.lst) : modname = $(modname-multi)
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quiet_cmd_cc_s_c = CC $(quiet_modtag) $@
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cmd_cc_s_c = $(CC) $(c_flags) -fverbose-asm -S -o $@ $<
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$(obj)/%.s: $(src)/%.c FORCE
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$(call if_changed_dep,cc_s_c)
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quiet_cmd_cc_i_c = CPP $(quiet_modtag) $@
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cmd_cc_i_c = $(CPP) $(c_flags) -o $@ $<
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$(obj)/%.i: $(src)/%.c FORCE
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$(call if_changed_dep,cc_i_c)
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quiet_cmd_cc_symtypes_c = SYM $(quiet_modtag) $@
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cmd_cc_symtypes_c = \
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$(CPP) -D__GENKSYMS__ $(c_flags) $< \
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| $(GENKSYMS) -T $@ >/dev/null; \
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test -s $@ || rm -f $@
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$(obj)/%.symtypes : $(src)/%.c FORCE
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$(call if_changed_dep,cc_symtypes_c)
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# C (.c) files
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# The C file is compiled and updated dependency information is generated.
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# (See cmd_cc_o_c + relevant part of rule_cc_o_c)
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quiet_cmd_cc_o_c = CC $(quiet_modtag) $@
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ifndef CONFIG_MODVERSIONS
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cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
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else
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# When module versioning is enabled the following steps are executed:
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# o compile a .tmp_<file>.o from <file>.c
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# o if .tmp_<file>.o doesn't contain a __ksymtab version, i.e. does
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# not export symbols, we just rename .tmp_<file>.o to <file>.o and
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# are done.
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# o otherwise, we calculate symbol versions using the good old
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# genksyms on the preprocessed source and postprocess them in a way
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# that they are usable as a linker script
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# o generate <file>.o from .tmp_<file>.o using the linker to
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# replace the unresolved symbols __crc_exported_symbol with
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# the actual value of the checksum generated by genksyms
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cmd_cc_o_c = $(CC) $(c_flags) -c -o $(@D)/.tmp_$(@F) $<
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cmd_modversions = \
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if $(OBJDUMP) -h $(@D)/.tmp_$(@F) | grep -q __ksymtab; then \
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$(CPP) -D__GENKSYMS__ $(c_flags) $< \
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| $(GENKSYMS) $(if $(KBUILD_SYMTYPES), \
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-T $(@D)/$(@F:.o=.symtypes)) -a $(ARCH) \
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> $(@D)/.tmp_$(@F:.o=.ver); \
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\
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$(LD) $(LDFLAGS) -r -o $@ $(@D)/.tmp_$(@F) \
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-T $(@D)/.tmp_$(@F:.o=.ver); \
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rm -f $(@D)/.tmp_$(@F) $(@D)/.tmp_$(@F:.o=.ver); \
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else \
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mv -f $(@D)/.tmp_$(@F) $@; \
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fi;
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endif
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ifdef CONFIG_FTRACE_MCOUNT_RECORD
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cmd_record_mcount = scripts/recordmcount.pl "$(ARCH)" \
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"$(OBJDUMP)" "$(OBJCOPY)" "$(CC)" "$(LD)" "$(NM)" "$(RM)" "$(MV)" "$(@)";
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endif
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define rule_cc_o_c
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$(call echo-cmd,checksrc) $(cmd_checksrc) \
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$(call echo-cmd,cc_o_c) $(cmd_cc_o_c); \
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$(cmd_modversions) \
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$(cmd_record_mcount) \
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scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' > \
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$(dot-target).tmp; \
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rm -f $(depfile); \
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mv -f $(dot-target).tmp $(dot-target).cmd
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endef
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# Built-in and composite module parts
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$(obj)/%.o: $(src)/%.c FORCE
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$(call cmd,force_checksrc)
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$(call if_changed_rule,cc_o_c)
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# Single-part modules are special since we need to mark them in $(MODVERDIR)
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$(single-used-m): $(obj)/%.o: $(src)/%.c FORCE
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$(call cmd,force_checksrc)
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$(call if_changed_rule,cc_o_c)
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@{ echo $(@:.o=.ko); echo $@; } > $(MODVERDIR)/$(@F:.o=.mod)
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quiet_cmd_cc_lst_c = MKLST $@
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cmd_cc_lst_c = $(CC) $(c_flags) -g -c -o $*.o $< && \
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$(CONFIG_SHELL) $(srctree)/scripts/makelst $*.o \
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System.map $(OBJDUMP) > $@
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$(obj)/%.lst: $(src)/%.c FORCE
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$(call if_changed_dep,cc_lst_c)
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# Compile assembler sources (.S)
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# ---------------------------------------------------------------------------
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modkern_aflags := $(AFLAGS_KERNEL)
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$(real-objs-m) : modkern_aflags := $(AFLAGS_MODULE)
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$(real-objs-m:.o=.s): modkern_aflags := $(AFLAGS_MODULE)
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quiet_cmd_as_s_S = CPP $(quiet_modtag) $@
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cmd_as_s_S = $(CPP) $(a_flags) -o $@ $<
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$(obj)/%.s: $(src)/%.S FORCE
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$(call if_changed_dep,as_s_S)
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quiet_cmd_as_o_S = AS $(quiet_modtag) $@
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cmd_as_o_S = $(CC) $(a_flags) -c -o $@ $<
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$(obj)/%.o: $(src)/%.S FORCE
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$(call if_changed_dep,as_o_S)
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targets += $(real-objs-y) $(real-objs-m) $(lib-y)
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targets += $(extra-y) $(MAKECMDGOALS) $(always)
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# Linker scripts preprocessor (.lds.S -> .lds)
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# ---------------------------------------------------------------------------
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quiet_cmd_cpp_lds_S = LDS $@
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cmd_cpp_lds_S = $(CPP) $(cpp_flags) -D__ASSEMBLY__ -o $@ $<
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$(obj)/%.lds: $(src)/%.lds.S FORCE
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$(call if_changed_dep,cpp_lds_S)
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# Build the compiled-in targets
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# ---------------------------------------------------------------------------
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# To build objects in subdirs, we need to descend into the directories
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$(sort $(subdir-obj-y)): $(subdir-ym) ;
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#
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# Rule to compile a set of .o files into one .o file
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#
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ifdef builtin-target
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quiet_cmd_link_o_target = LD $@
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# If the list of objects to link is empty, just create an empty built-in.o
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cmd_link_o_target = $(if $(strip $(obj-y)),\
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$(LD) $(ld_flags) -r -o $@ $(filter $(obj-y), $^) \
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$(cmd_secanalysis),\
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rm -f $@; $(AR) rcs $@)
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$(builtin-target): $(obj-y) FORCE
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$(call if_changed,link_o_target)
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targets += $(builtin-target)
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endif # builtin-target
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#
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# Rule to create modules.order file
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#
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# Create commands to either record .ko file or cat modules.order from
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# a subdirectory
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modorder-cmds = \
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$(foreach m, $(modorder), \
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$(if $(filter %/modules.order, $m), \
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cat $m;, echo kernel/$m;))
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$(modorder-target): $(subdir-ym) FORCE
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$(Q)(cat /dev/null; $(modorder-cmds)) > $@
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#
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# Rule to compile a set of .o files into one .a file
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#
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ifdef lib-target
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quiet_cmd_link_l_target = AR $@
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cmd_link_l_target = rm -f $@; $(AR) rcs $@ $(lib-y)
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$(lib-target): $(lib-y) FORCE
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$(call if_changed,link_l_target)
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targets += $(lib-target)
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endif
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#
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# Rule to link composite objects
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#
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# Composite objects are specified in kbuild makefile as follows:
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# <composite-object>-objs := <list of .o files>
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# or
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# <composite-object>-y := <list of .o files>
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link_multi_deps = \
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$(filter $(addprefix $(obj)/, \
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$($(subst $(obj)/,,$(@:.o=-objs))) \
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$($(subst $(obj)/,,$(@:.o=-y)))), $^)
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quiet_cmd_link_multi-y = LD $@
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cmd_link_multi-y = $(LD) $(ld_flags) -r -o $@ $(link_multi_deps) $(cmd_secanalysis)
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quiet_cmd_link_multi-m = LD [M] $@
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cmd_link_multi-m = $(cmd_link_multi-y)
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# We would rather have a list of rules like
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# foo.o: $(foo-objs)
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# but that's not so easy, so we rather make all composite objects depend
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# on the set of all their parts
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$(multi-used-y) : %.o: $(multi-objs-y) FORCE
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$(call if_changed,link_multi-y)
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$(multi-used-m) : %.o: $(multi-objs-m) FORCE
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$(call if_changed,link_multi-m)
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@{ echo $(@:.o=.ko); echo $(link_multi_deps); } > $(MODVERDIR)/$(@F:.o=.mod)
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targets += $(multi-used-y) $(multi-used-m)
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# Descending
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# ---------------------------------------------------------------------------
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PHONY += $(subdir-ym)
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$(subdir-ym):
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$(Q)$(MAKE) $(build)=$@
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# Add FORCE to the prequisites of a target to force it to be always rebuilt.
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# ---------------------------------------------------------------------------
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PHONY += FORCE
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FORCE:
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# Read all saved command lines and dependencies for the $(targets) we
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# may be building above, using $(if_changed{,_dep}). As an
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# optimization, we don't need to read them if the target does not
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# exist, we will rebuild anyway in that case.
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targets := $(wildcard $(sort $(targets)))
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cmd_files := $(wildcard $(foreach f,$(targets),$(dir $(f)).$(notdir $(f)).cmd))
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ifneq ($(cmd_files),)
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include $(cmd_files)
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endif
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# Declare the contents of the .PHONY variable as phony. We keep that
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# information in a variable se we can use it in if_changed and friends.
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.PHONY: $(PHONY)
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