[PATCH 1/1] kbuild: record real-prereqs in .cmd files

[Luis Augenstein <luis.augenstein@tngtech.com>]

Record $(real-prereqs), the non-phony prerequisites of the target, in a
new metadata field:

    make_prereqs_<target> := <prerequisites>

Write the field from both cmd_and_savecmd and cmd_and_fixdep.

Update scripts/make_fit.py to read only savedcmd_* instead of parsing the
complete .cmd file.

Ignore make_prereqs_* in KernelSbom.

Link: https://lore.kernel.org/r/a01233b9-23a2-4666-91ed-f1cf030dcb9f@tngtech.com
Assisted-by: Cursor:GPT-5.6 Sol
Co-developed-by: Maximilian Huber <maximilian.huber@tngtech.com>
Signed-off-by: Maximilian Huber <maximilian.huber@tngtech.com>
Signed-off-by: Luis Augenstein <luis.augenstein@tngtech.com>
---
 scripts/Kbuild.include                  |  9 +++++++--
 scripts/basic/fixdep.c                  | 16 ++++++++++------
 scripts/make_fit.py                     |  2 +-
 scripts/sbom/sbom/cmd_graph/cmd_file.py |  4 ++++
 4 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 8c311b997e2..6daa244ba0e 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 +201,16 @@ if_changed = $(if $(if-changed-cond),$(cmd_and_savecmd),@:)
 
 cmd_and_savecmd =                                                            \
 	$(cmd);                                                              \
-	printf '%s\n' 'savedcmd_$@ := $(make-cmd)' > $(dot-target).cmd
+	printf '%s\n\n%s\n' 'savedcmd_$@ := $(make-cmd)'                    \
+		'make_prereqs_$@ := $(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 cdd5da7e009..03831a6f8f7 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>
  *
  * 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);
 }
 
@@ -409,17 +411,19 @@ static void parse_dep_file(char *p, const char *target)
 
 int main(int argc, char *argv[])
 {
-	const char *depfile, *target, *cmdline;
+	const char *depfile, *target, *cmdline, *prereqs;
 	void *buf;
 
-	if (argc != 4)
+	if (argc != 5)
 		usage();
 
 	depfile = argv[1];
 	target = argv[2];
 	cmdline = argv[3];
+	prereqs = argv[4];
 
 	printf("savedcmd_%s := %s\n\n", target, cmdline);
+	printf("make_prereqs_%s := %s\n\n", target, prereqs);
 
 	buf = read_file(depfile);
 	parse_dep_file(buf, target);
diff --git a/scripts/make_fit.py b/scripts/make_fit.py
index 15ba26974fd..346e8a7ec12 100755
--- a/scripts/make_fit.py
+++ b/scripts/make_fit.py
@@ -288,7 +288,7 @@ def process_dtb(fname, args):
         path, basename = os.path.split(fname)
         cmd_fname = os.path.join(path, f'.{basename}.cmd')
         with open(cmd_fname, 'r', encoding='ascii') as inf:
-            cmd = inf.read()
+            cmd = inf.readline()
 
         if 'scripts/dtc/fdtoverlay' in cmd:
             # This depends on the structure of the composite DTB command
diff --git a/scripts/sbom/sbom/cmd_graph/cmd_file.py b/scripts/sbom/sbom/cmd_graph/cmd_file.py
index dcd63e284a3..08819b4d117 100644
--- a/scripts/sbom/sbom/cmd_graph/cmd_file.py
+++ b/scripts/sbom/sbom/cmd_graph/cmd_file.py
@@ -50,6 +50,10 @@ class CmdFile:
         with open(cmd_file_path, "rt", encoding="utf-8") as f:
             lines = [line.strip() for line in f.readlines() if line.strip() != "" and not line.startswith("#")]
 
+        # make_prereqs_* is recorded for future use. Ignore it for now to
+        # preserve the existing parser behavior.
+        lines = [line for line in lines if not line.startswith("make_prereqs_")]
+
         # savedcmd
         match = SAVEDCMD_PATTERN.match(lines[0] if lines else "")
         if match is None:
-- 
2.43.0