[PATCH v3 4/7] kbuild: record cmd-prereqs in .cmd files

[Luis Augenstein]

Record $(cmd-prereqs), i.e. $(real-prereqs) with the deps_*
dependencies filtered out, in a new .cmd file metadata field:

    make_prereqs_<target> := <prerequisites>

On an incremental build, deps_<target> holds the dependencies
recorded from the depfile of the previous build. Those are filtered
out from $(real-prereqs), even if they no longer appear in the
current depfile. fixdep additionally filters the dependencies
collected from the current depfile, so that they are not recorded in
both deps_<target> and make_prereqs_<target>. This keeps the field
consistent between clean and incremental builds.

Link: https://lore.kernel.org/r/a01233b9-23a2-4666-91ed-f1cf030dcb9f@xxxxxxxxxxx
Assisted-by: LLM
Co-developed-by: Maximilian Huber <maximilian.huber@xxxxxxxxxxx>
Signed-off-by: Maximilian Huber <maximilian.huber@xxxxxxxxxxx>
Signed-off-by: Luis Augenstein <luis.augenstein@xxxxxxxxxxx>
---
 scripts/Kbuild.include | 10 ++++++--
 scripts/basic/fixdep.c | 54 +++++++++++++++++++++++++++++++++++++-----
 2 files changed, 56 insertions(+), 8 deletions(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 8c311b997e2..7790519f92f 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -181,6 +181,9 @@ endif
 # (needed for the shell)
 make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst $$,$$$$,$(cmd_$(1)))))
 
+# prerequisites to record in .cmd files, excluding those covered in deps_*
+cmd-prereqs = $(call escsq,$(filter-out $(deps_$@), $(real-prereqs)))
+
 # Find any prerequisites that are newer than target or that do not exist.
 # PHONY targets skipped in both cases.
 # If there is no prerequisite other than phony targets, $(newer-prereqs) becomes
@@ -198,14 +201,17 @@ if_changed = $(if $(if-changed-cond),$(cmd_and_savecmd),@:)
 
 cmd_and_savecmd =                                                            \
 	$(cmd);                                                              \
-	printf '%s\n' 'savedcmd_$@ := $(make-cmd)' > $(dot-target).cmd
+	printf '%s\n'                                                        \
+		'savedcmd_$@ := $(make-cmd)' ''                              \
+		'make_prereqs_$@ := $(cmd-prereqs)' > $(dot-target).cmd
 
 # Execute the command and also postprocess generated .d dependencies file.
 if_changed_dep = $(if $(if-changed-cond),$(cmd_and_fixdep),@:)
 
 cmd_and_fixdep =                                                             \
 	$(cmd);                                                              \
-	$(objtree)/scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).cmd;\
+	$(objtree)/scripts/basic/fixdep $(depfile) $@ '$(make-cmd)'          \
+		'$(cmd-prereqs)' > $(dot-target).cmd;                        \
 	rm -f $(depfile)
 
 # Usage: $(call if_changed_rule,foo)
diff --git a/scripts/basic/fixdep.c b/scripts/basic/fixdep.c
index f514ef606ec..005c1c3df49 100644
--- a/scripts/basic/fixdep.c
+++ b/scripts/basic/fixdep.c
@@ -62,15 +62,17 @@
  *
  * It is invoked as
  *
- *   fixdep <depfile> <target> <cmdline>
+ *   fixdep <depfile> <target> <cmdline> <prereqs>
  *
  * and will read the dependency file <depfile>
  *
  * The transformed dependency snipped is written to stdout.
  *
- * It first generates a line
+ * It first generates the lines
  *
- *   savedcmd_<target> = <cmdline>
+ *   savedcmd_<target> := <cmdline>
+ *
+ *   make_prereqs_<target> := <prereqs_without_deps>
  *
  * and then basically copies the .<target>.d file to stdout, in the
  * process filtering out the dependency on autoconf.h and adding
@@ -103,7 +105,7 @@
 
 static void usage(void)
 {
-	fprintf(stderr, "Usage: fixdep <depfile> <target> <cmdline>\n");
+	fprintf(stderr, "Usage: fixdep <depfile> <target> <cmdline> <prereqs>\n");
 	exit(1);
 }
 
@@ -478,23 +480,63 @@ static void print_dep_file(const char *target, const struct dep_info *info)
 	printf("$(deps_%s):\n", target);
 }
 
+/*
+ * Print make_prereqs_<target> from prereqs, excluding the deps listed
+ * in info.
+ */
+static void print_make_prereqs(const char *target, const char *prereqs,
+			       const struct dep_info *info)
+{
+	struct item *seen_prereqs_hashtab[HASHSZ] = {};
+	const struct dep_item *dep;
+	const char *p = prereqs;
+
+	for (dep = info->deps; dep; dep = dep->next)
+		in_hashtable(dep->name, strlen(dep->name),
+			     seen_prereqs_hashtab);
+
+	printf("make_prereqs_%s :=", target);
+
+	while (*p) {
+		const char *start;
+		int len;
+
+		while (*p == ' ' || *p == '\t')
+			p++;
+		if (!*p)
+			break;
+
+		start = p;
+		while (*p && *p != ' ' && *p != '\t')
+			p++;
+		len = p - start;
+
+		if (!in_hashtable(start, len, seen_prereqs_hashtab))
+			printf(" %.*s", len, start);
+	}
+
+	printf("\n\n");
+}
+
 int main(int argc, char *argv[])
 {
-	const char *depfile, *target, *cmdline;
+	const char *depfile, *target, *cmdline, *prereqs;
 	struct dep_info info;
 	void *buf;
 
-	if (argc != 4)
+	if (argc != 5)
 		usage();
 
 	depfile = argv[1];
 	target = argv[2];
 	cmdline = argv[3];
+	prereqs = argv[4];
 
 	buf = read_file(depfile);
 	info = parse_dep_file(buf);
 
 	printf("savedcmd_%s := %s\n\n", target, cmdline);
+	print_make_prereqs(target, prereqs, &info);
 	print_dep_file(target, &info);
 
 	free_dep_info(&info);
-- 
2.43.0