[PATCH 18/37] modpost: invoke modpost only when input files are updated

[Masahiro Yamada <masahiroy@xxxxxxxxxx>]

Currently, the second pass of modpost is always invoked when you run
'make' or 'make modules' even if none of modules is changed.

Use if_changed to invoke it only when it is necessary.

Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
---

 scripts/Makefile.modpost | 20 ++++++++++++++++----
 scripts/mod/modpost.c    | 32 +++++++++++++++++++++-----------
 2 files changed, 37 insertions(+), 15 deletions(-)

diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 6db692a5d547..7d564a39f938 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -90,20 +90,25 @@ endif
 
 # modpost options for modules (both in-kernel and external)
 MODPOST += \
-	$(addprefix -i ,$(input-symdump)) \
+	$(addprefix -i ,$(wildcard $(input-symdump))) \
 	$(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS)$(KBUILD_NSDEPS),-N)
 
 ifneq ($(findstring i,$(filter-out --%,$(MAKEFLAGS))),)
 MODPOST += -n
 endif
 
+$(input-symdump):
+	@:
+
 # Read out modules.order to pass in modpost.
 # Otherwise, allmodconfig would fail with "Argument list too long".
 quiet_cmd_modpost = MODPOST $@
-      cmd_modpost = sed 's/ko$$/o/' $(MODORDER) | $(MODPOST) -T -
+      cmd_modpost = sed 's/ko$$/o/' $< | $(MODPOST) -T -
 
-$(output-symdump): FORCE
-	$(call cmd,modpost)
+$(output-symdump): $(MODORDER) $(input-symdump) FORCE
+	$(call if_changed,modpost)
+
+targets += $(output-symdump)
 
 __modpost: $(output-symdump)
 ifneq ($(KBUILD_MODPOST_NOFINAL),1)
@@ -113,6 +118,13 @@ endif
 PHONY += FORCE
 FORCE:
 
+existing-targets := $(wildcard $(sort $(targets)))
+
+-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
+
+PHONY += FORCE
+FORCE:
+
 endif
 
 .PHONY: $(PHONY)
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 4a2f27d97bf1..b839c48689df 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -2375,6 +2375,25 @@ static void add_srcversion(struct buffer *b, struct module *mod)
 	}
 }
 
+static void write_buf(struct buffer *b, const char *fname)
+{
+	FILE *file;
+
+	file = fopen(fname, "w");
+	if (!file) {
+		perror(fname);
+		exit(1);
+	}
+	if (fwrite(b->p, 1, b->pos, file) != b->pos) {
+		perror(fname);
+		exit(1);
+	}
+	if (fclose(file) != 0) {
+		perror(fname);
+		exit(1);
+	}
+}
+
 static void write_if_changed(struct buffer *b, const char *fname)
 {
 	char *tmp;
@@ -2407,16 +2426,7 @@ static void write_if_changed(struct buffer *b, const char *fname)
  close_write:
 	fclose(file);
  write:
-	file = fopen(fname, "w");
-	if (!file) {
-		perror(fname);
-		exit(1);
-	}
-	if (fwrite(b->p, 1, b->pos, file) != b->pos) {
-		perror(fname);
-		exit(1);
-	}
-	fclose(file);
+	write_buf(b, fname);
 }
 
 /* parse Module.symvers file. line format:
@@ -2508,7 +2518,7 @@ static void write_dump(const char *fname)
 			symbol = symbol->next;
 		}
 	}
-	write_if_changed(&buf, fname);
+	write_buf(&buf, fname);
 	free(buf.p);
 }
 
-- 
2.25.1