Linux makefile analysis-vmlinux generation

1. Top-level makefile tracking:

Find the vmlinux target

# Vmlinux image-including updated kernel symbols

Vmlinux: $ (vmlinux-LDS) $ (vmlinux-init) $ (vmlinux-Main) $ (kallsyms. O) Force

Ifdef config_headers_check

$ (Q) $ (make)-F $ (srctree)/makefile headers_check

Endif

$ (Call if_changed_rule, vmlinux __)

$ (Q) $ (make)-F $ (srctree)/scripts/makefile. modpost $ @

$ (Q) Rm-F. old_version

@ Echo "================================== vmlinux ================ ======================"

@ Echo $ (vmlinux-LDS) $ (vmlinux-init) $ (vmlinux-Main) $ (kallsyms. O)

@ CP vmlinux. Full

Find vmlinux-init:

Vmlinux-init: = $ (Head-y) $ (init-y)

Head-Y is a machine-related variable, defined in makefile in arch:

Head-Y: = ARCH/MIPS/kernel/head. o arch/MIPS/kernel/init_task.o

This makefile is included through include $ (srctree)/ARCH/$ (srcarch)/makefile.

Init-y is defined in makefile:

Init-Y: = init/

...

Init-Y: = $ (patsubst %/, %/built-in.o, $ (init-y ))

The final result is:

Init-Y: = init/built-in.o. This build-in.o this intermediate file may have heard of, in fact, this file is the directory under all obj-y to synthesize.

In addition, you can find the following two variables:

Vmlinux-Main :=$ (core-y) $ (libs-y) $ (drivers-y) $ (net-y)

Vmlinux-LDS: = ARCH/$ (ARCH)/kernel/vmlinux. LDS

Vmlinux-dirs

Pay attention to the following sentence:

$ (Sort $ (vmlinux-init) $ (vmlinux-Main) $ (vmlinux-LDS): $ (vmlinux-dirs );

This statement is generated by dependency before executing the vmlinux target. Let's take a look at the most critical vmlinux-dirs.

Vmlinux-dirs :=$ (patsubst %/, %, $ (filter %/, $ (init-y) $ (init-m )\

$ (Core-y) $ (core-m) $ (drivers-y) $ (drivers-m )\

$ (Net-y) $ (net-m) $ (libs-y) $ (libs-m )))

In fact, $ (vmlinux-dirs) is still a goal.

Phony + = $ (vmlinux-dirs)

$ (Vmlinux-dirs): prepare scripts

$ (Q) $ (make) $ (build) =$ @

Makefile. kbuild rules are used. The directory in vmlinux-dirs is recursively processed to generate those. O files, especially the build-in.o. When executing vmlinux, the $ (vmlinux-dirs) target will certainly be executed first.

Link to vmlinux

Where is the link? Let's see what follows endif:

$ (Call if_changed_rule, vmlinux __)

$ (Q) $ (make)-F $ (srctree)/scripts/makefile. modpost $ @

$ (Call if_changed_rule, vmlinux _) will call rule_vmlinux _, that is, the following content:

# Link of vmlinux

# If config_kallsyms is set. version is already updated

# Generate system. Map and verify that the content is consistent

# Use + In Front Of The vmlinux_version rule to silent warning with make-J2

# First Command is ':' to allow us to use + in front of the rule

Define rule_vmlinux __

:

$ (If $ (config_kallsyms), + $ (call cmd, vmlinux_version ))

$ (Call cmd, vmlinux __)

$ (Q) echo 'cmd _ $ @: = $ (cmd_vmlinux _) '> $ (@ d)/. $ (@ f). cmd

$ (Q) $ (if $ (quiet) pai_sysmap ),\

Echo '$ (quiet) cmd_sysmap) system. map '&&)\

$ (Pai_sysmap) $ @ system. Map ;\

If [$? -Ne 0]; then \

Rm-F $ @;\

/Bin/false ;\

FI;

$ (Verify_kallsyms)

Endef

The command vmlinux __, _ vmlinux_version and sysmap are defined here. The vmlinux _ command contains the LD link to generate vmlinux.

# Rule to link vmlinux-also used during config_kallsyms

# May be overridden by arch/$ (ARCH)/makefile

Quiet_cmd_vmlinux __? = LD $ @

Cmd_vmlinux __? = $ (LD) $ (ldflags) $ (ldflags_vmlinux)-o $ @\

-T $ (vmlinux-LDS) $ (vmlinux-init )\

-- Start-group $ (vmlinux-Main) -- end-group \

$ (Filter-out $ (vmlinux-LDS) $ (vmlinux-init) $ (vmlinux-Main) Force, $ ^)

# Generate new vmlinux version

Quiet_cmd_vmlinux_version = gen. Version

Pai_vmlinux_version = set-E ;\

If [! -R. Version]; then \

Rm-F. version ;\

Echo 1>. version ;\

Else \

MV. version. old_version ;\

Expr 0 $ (Cat. old_version) + 1>. version ;\

FI ;\

$ (Make) $ (build) = init

# Generate system. Map

Quiet_pai_sysmap = sysmap

Performance_sysmap = $ (config_shell) $ (srctree)/scripts/mksysmap

2. makefile. kbuild rules:

$ (Q) $ (make)-F $ (if $ (kbuild_src), $ (srctree)/) scripts/makefile. Build \

OBJ = $ (vmlinux-dirs)

Find the target _ build:

_ Build: $ (if $ (kbuild_builtin), $ (builtin-target) $ (Lib-target) $ (extra-y ))\

$ (If $ (kbuild_modules), $ (obj-m ))\

$ (Subdir-ym) $ (always)

@:

Because kbuild_builtin is initialized to 1 in the top-layer makefile, the dependency of this rule has a builtin-target variable:

Ifneq ($ (Strip $ (obj-y) $ (obj-m) $ (obj-N) $ (obj-) $ (Lib-target )),)

Builtin-target: = $ (OBJ)/built-in.o

Endif

The variable obj is the directory specified by the vmlinux-dirs variable. So here we will build $ (vmlinux-dirs)/built-in.o goals:

Ifdef builtin-Target

Quiet_cmd_link_o_target = LD $ @

# If the list of objects to link is empty, just create an empty built-in.o

Export _link_o_target =$ (if $ (Strip $ (obj-y )),\

$ (LD) $ (ld_flags)-R-o $ @ $ (filter $ (obj-y), $ ^ ),\

Rm-F $ @; $ (AR) RCS $ @)

The above is generated by. o specified by obj-y $ (vmlinux-dirs)/built-in.o.

$ (Builtin-target): $ (obj-y) Force

$ (Call if_changed, link_o_target)

The MAKEFILE file in the directory specified by the vmlinux-dirs variable is included below. In these makefile files, the obj-y variable is specified, which specifies some *. O target files,

Kbuild-Dir: = $ (if $ (filter/%, $ (SRC), $ (SRC), $ (srctree)/$ (SRC ))

Include $ (if $ (wildcard $ (kbuild-DIR)/kbuild), $ (kbuild-DIR)/kbuild, $ (kbuild-DIR)/makefile)

These *. o file generation methods are specified by the pattern rules of the scripts/makefile. Build File.

%. O: %. c force

$ (Call cmd, force_checksrc)

$ (Call if_changed_rule, cc_o_c)

The above will generate the. o specified by obj-y.

Through the above steps, the target specified by the vmlinux-init variable is compiled and linked. the build of the target specified by the vmlinux-main variable is similar to this.

Tianxingjian, a gentleman is always striving for self-improvement