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-rw-r--r--Documentation/kbuild/makefiles.rst45
1 files changed, 44 insertions, 1 deletions
diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst
index 6515ebc12b6f..b81b8913a5a3 100644
--- a/Documentation/kbuild/makefiles.rst
+++ b/Documentation/kbuild/makefiles.rst
@@ -368,6 +368,14 @@ more details, with real examples.
subdir-ccflags-y := -Werror
+ ccflags-remove-y, asflags-remove-y
+ These flags are used to remove particular flags for the compiler,
+ assembler invocations.
+
+ Example::
+
+ ccflags-remove-$(CONFIG_MCOUNT) += -pg
+
CFLAGS_$@, AFLAGS_$@
CFLAGS_$@ and AFLAGS_$@ only apply to commands in current
kbuild makefile.
@@ -375,6 +383,9 @@ more details, with real examples.
$(CFLAGS_$@) specifies per-file options for $(CC). The $@
part has a literal value which specifies the file that it is for.
+ CFLAGS_$@ has the higher priority than ccflags-remove-y; CFLAGS_$@
+ can re-add compiler flags that were removed by ccflags-remove-y.
+
Example::
# drivers/scsi/Makefile
@@ -387,6 +398,9 @@ more details, with real examples.
$(AFLAGS_$@) is a similar feature for source files in assembly
languages.
+ AFLAGS_$@ has the higher priority than asflags-remove-y; AFLAGS_$@
+ can re-add assembler flags that were removed by asflags-remove-y.
+
Example::
# arch/arm/kernel/Makefile
@@ -735,6 +749,10 @@ Both possibilities are described in the following.
hostprogs := lxdialog
always-y := $(hostprogs)
+ Kbuild provides the following shorthand for this:
+
+ hostprogs-always-y := lxdialog
+
This will tell kbuild to build lxdialog even if not referenced in
any rule.
@@ -817,7 +835,32 @@ The syntax is quite similar. The difference is to use "userprogs" instead of
5.4 When userspace programs are actually built
----------------------------------------------
- Same as "When host programs are actually built".
+ Kbuild builds userspace programs only when told to do so.
+ There are two ways to do this.
+
+ (1) Add it as the prerequisite of another file
+
+ Example::
+
+ #net/bpfilter/Makefile
+ userprogs := bpfilter_umh
+ $(obj)/bpfilter_umh_blob.o: $(obj)/bpfilter_umh
+
+ $(obj)/bpfilter_umh is built before $(obj)/bpfilter_umh_blob.o
+
+ (2) Use always-y
+
+ Example::
+
+ userprogs := binderfs_example
+ always-y := $(userprogs)
+
+ Kbuild provides the following shorthand for this:
+
+ userprogs-always-y := binderfs_example
+
+ This will tell Kbuild to build binderfs_example when it visits this
+ Makefile.
6 Kbuild clean infrastructure
=============================