Merge tag 'kbuild-7.2-2' of git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux

Pull more Kbuild updates from Nathan Chancellor:

 - Link host programs with ld.lld when $(LLVM) is set to match user's
   expectations that LLVM will be used exclusively during the build
   process

 - Fix modpost warnings from static variable name promotion that can
   happen more aggressively with the recently merged distributed ThinLTO
   support

 - Add an optional warning for user-supplied Kconfig values that changed
   after processing, such as out of range values or options that have
   incorrect / missing dependencies

* tag 'kbuild-7.2-2' of git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux:
  kconfig: add optional warnings for changed input values
  modpost: Ignore Clang LTO suffixes in symbol matching
  kbuild: Use ld.lld for linking host programs when LLVM is set

Documentation/kbuild/kconfig.rst

@@ -59,6 +59,11 @@ Environment variables for ``*config``:
     This environment variable makes Kconfig warn about all unrecognized
     symbols in the config input.
 
+``KCONFIG_WARN_CHANGED_INPUT``
+    If set to a non-blank value, Kconfig prints optional warnings for
+    user-provided values that change after Kconfig resolves dependencies
+    or applies other constraints such as ranges.
+
 ``KCONFIG_WERROR``
     If set, Kconfig treats warnings as errors.
 

Makefile

@@ -528,6 +528,9 @@ OBJCOPY		= $(LLVM_PREFIX)llvm-objcopy$(LLVM_SUFFIX)
 OBJDUMP		= $(LLVM_PREFIX)llvm-objdump$(LLVM_SUFFIX)
 READELF		= $(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX)
 STRIP		= $(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX)
+ifeq ($(filter -fuse-ld=% --ld-path=%,$(KBUILD_HOSTLDFLAGS)),)
+KBUILD_HOSTLDFLAGS += -fuse-ld=lld
+endif
 else
 CC		= $(CROSS_COMPILE)gcc
 LD		= $(CROSS_COMPILE)ld

scripts/kconfig/confdata.c

@@ -206,6 +206,78 @@ static void conf_message(const char *fmt, ...)
 	va_end(ap);
 }
 
+static void conf_changed_input_warning(const char *s)
+{
+	fputs(s, stderr);
+}
+
+static bool conf_warn_changed_input_enabled(void)
+{
+	const char *env = getenv("KCONFIG_WARN_CHANGED_INPUT");
+
+	return env && *env;
+}
+
+static const char *sym_get_user_value_string(struct symbol *sym)
+{
+	switch (sym->type) {
+	case S_BOOLEAN:
+	case S_TRISTATE:
+		switch (sym->def[S_DEF_USER].tri) {
+		case yes:
+			return "y";
+		case mod:
+			return "m";
+		default:
+			return "n";
+		}
+	default:
+		return sym->def[S_DEF_USER].val ?: "";
+	}
+}
+
+static bool sym_user_value_changed(struct symbol *sym)
+{
+	if (!sym_has_value(sym) || sym->type == S_UNKNOWN)
+		return false;
+
+	switch (sym->type) {
+	case S_BOOLEAN:
+	case S_TRISTATE:
+		return sym->def[S_DEF_USER].tri != sym_get_tristate_value(sym);
+	default:
+		return strcmp(sym_get_user_value_string(sym),
+			      sym_get_string_value(sym));
+	}
+}
+
+static void conf_clear_written_flags(void)
+{
+	struct symbol *sym;
+
+	for_all_symbols(sym)
+		sym->flags &= ~SYMBOL_WRITTEN;
+}
+
+static void conf_append_changed_input_warning(struct gstr *gs,
+					      struct symbol *sym,
+					      bool *changed_input_found)
+{
+	if (!sym_user_value_changed(sym))
+		return;
+
+	if (!*changed_input_found) {
+		str_printf(gs,
+			   "warning: user-provided values changed by Kconfig:\n");
+		*changed_input_found = true;
+	}
+
+	str_printf(gs, "  %s%s: %s -> %s\n",
+		   CONFIG_, sym->name,
+		   sym_get_user_value_string(sym),
+		   sym_get_string_value(sym));
+}
+
 const char *conf_get_configname(void)
 {
 	char *name = getenv("KCONFIG_CONFIG");
@@ -759,11 +831,15 @@ int conf_write_defconfig(const char *filename)
 {
 	struct symbol *sym;
 	struct menu *menu;
+	struct gstr gs;
 	FILE *out;
+	bool warn_changed_input = conf_warn_changed_input_enabled();
+	bool changed_input_found = false;
 
 	out = fopen(filename, "w");
 	if (!out)
 		return 1;
+	gs = str_new();
 
 	sym_clear_all_valid();
 
@@ -772,10 +848,14 @@ int conf_write_defconfig(const char *filename)
 
 		sym = menu->sym;
 
-		if (!sym || sym_is_choice(sym))
+		if (!sym || sym_is_choice(sym) || sym->flags & SYMBOL_WRITTEN)
 			continue;
 
 		sym_calc_value(sym);
+		if (warn_changed_input)
+			conf_append_changed_input_warning(&gs, sym,
+							  &changed_input_found);
+		sym->flags |= SYMBOL_WRITTEN;
 		if (!(sym->flags & SYMBOL_WRITE))
 			continue;
 		sym->flags &= ~SYMBOL_WRITE;
@@ -798,6 +878,13 @@ int conf_write_defconfig(const char *filename)
 		print_symbol_for_dotconfig(out, sym);
 	}
 	fclose(out);
+
+	conf_clear_written_flags();
+
+	if (changed_input_found)
+		conf_changed_input_warning(str_get(&gs));
+
+	str_free(&gs);
 	return 0;
 }
 
@@ -809,7 +896,10 @@ int conf_write(const char *name)
 	const char *str;
 	char tmpname[PATH_MAX + 1], oldname[PATH_MAX + 1];
 	char *env;
+	struct gstr gs;
 	bool need_newline = false;
+	bool warn_changed_input = conf_warn_changed_input_enabled();
+	bool changed_input_found = false;
 
 	if (!name)
 		name = conf_get_configname();
@@ -838,6 +928,7 @@ int conf_write(const char *name)
 	}
 	if (!out)
 		return 1;
+	gs = str_new();
 
 	conf_write_heading(out, &comment_style_pound);
 
@@ -859,13 +950,16 @@ int conf_write(const char *name)
 		} else if (!sym_is_choice(sym) &&
 			   !(sym->flags & SYMBOL_WRITTEN)) {
 			sym_calc_value(sym);
+			if (warn_changed_input)
+				conf_append_changed_input_warning(&gs, sym,
+								  &changed_input_found);
+			sym->flags |= SYMBOL_WRITTEN;
 			if (!(sym->flags & SYMBOL_WRITE))
 				goto next;
 			if (need_newline) {
 				fprintf(out, "\n");
 				need_newline = false;
 			}
-			sym->flags |= SYMBOL_WRITTEN;
 			print_symbol_for_dotconfig(out, sym);
 		}
 
@@ -892,8 +986,12 @@ int conf_write(const char *name)
 	}
 	fclose(out);
 
-	for_all_symbols(sym)
-		sym->flags &= ~SYMBOL_WRITTEN;
+	conf_clear_written_flags();
+
+	if (changed_input_found)
+		conf_changed_input_warning(str_get(&gs));
+
+	str_free(&gs);
 
 	if (*tmpname) {
 		if (is_same(name, tmpname)) {

scripts/kconfig/tests/conftest.py

@@ -37,7 +37,8 @@ class Conf:
 
     # runners
     def _run_conf(self, mode, dot_config=None, out_file='.config',
-                  interactive=False, in_keys=None, extra_env={}):
+                  interactive=False, in_keys=None, extra_env={},
+                  silent=False):
         """Run text-based Kconfig executable and save the result.
 
         mode: input mode option (--oldaskconfig, --defconfig=<file> etc.)
@@ -48,7 +49,10 @@ class Conf:
         extra_env: additional environments
         returncode: exit status of the Kconfig executable
         """
-        command = [CONF_PATH, mode, 'Kconfig']
+        command = [CONF_PATH]
+        if silent:
+            command.append('-s')
+        command += [mode, 'Kconfig']
 
         # Override 'srctree' environment to make the test as the top directory
         extra_env['srctree'] = self._test_dir

scripts/kconfig/tests/warn_changed_input/Kconfig

@@ -0,0 +1,40 @@
+# SPDX-License-Identifier: GPL-2.0
+
+config DEP
+	bool "DEP"
+	help
+	  Test dependency symbol for Kconfig warning coverage.
+	  This is used by the warn_changed_input selftest.
+	  It intentionally stays unset in the input fragment.
+	  The test checks how dependent user input is adjusted.
+
+config A
+	bool "A"
+	depends on DEP
+	help
+	  Test bool symbol for changed-input diagnostics.
+	  The input fragment requests this symbol as built-in.
+	  The unmet dependency on DEP forces the final value to n.
+	  The warning should report that downgrade.
+
+config NUM
+	int "NUM"
+	range 10 20
+	help
+	  Test integer symbol for changed-input diagnostics.
+	  The input fragment requests a value outside the allowed range.
+	  Kconfig resolves it to the constrained in-range value.
+	  The warning should report that adjustment.
+
+config DUP
+	bool "DUP"
+	depends on DEP
+	help
+	  Test duplicate-definition handling for changed-input diagnostics.
+	  The input fragment requests this symbol as built-in.
+	  The duplicate definition below must not produce a duplicate warning.
+	  This keeps the warning output stable for repeated menu entries.
+
+config DUP
+	bool
+	depends on DEP

scripts/kconfig/tests/warn_changed_input/__init__.py

@@ -0,0 +1,33 @@
+# SPDX-License-Identifier: GPL-2.0
+"""
+Test optional warnings for user-provided values changed by Kconfig.
+
+Warnings should stay disabled by default, and should only appear when
+KCONFIG_WARN_CHANGED_INPUT is enabled.
+"""
+
+
+def test(conf):
+    assert conf.olddefconfig('config') == 0
+    assert 'user-provided values changed by Kconfig' not in conf.stderr
+
+    assert conf._run_conf('--olddefconfig', dot_config='config',
+                          extra_env={
+                              'KCONFIG_WARN_CHANGED_INPUT': '1',
+                          }) == 0
+    assert conf.stderr_contains('expected_stderr')
+    assert conf.config_matches('expected_config')
+
+    assert conf._run_conf('--olddefconfig', dot_config='config',
+                          extra_env={
+                              'KCONFIG_WARN_CHANGED_INPUT': '1',
+                          }, silent=True) == 0
+    assert conf.stderr_contains('expected_stderr')
+
+    assert conf._run_conf('--savedefconfig=defconfig', dot_config='config',
+                          out_file='defconfig',
+                          extra_env={
+                              'KCONFIG_WARN_CHANGED_INPUT': '1',
+                          }) == 0
+    assert conf.stderr_contains('expected_stderr')
+    assert conf.config_matches('expected_defconfig')

scripts/kconfig/tests/warn_changed_input/config

@@ -0,0 +1,3 @@
+CONFIG_A=y
+CONFIG_NUM=30
+CONFIG_DUP=y

scripts/kconfig/tests/warn_changed_input/expected_config

@@ -0,0 +1,6 @@
+#
+# Automatically generated file; DO NOT EDIT.
+# Main menu
+#
+# CONFIG_DEP is not set
+CONFIG_NUM=20

scripts/kconfig/tests/warn_changed_input/expected_defconfig

@@ -0,0 +1 @@
+CONFIG_NUM=20

scripts/kconfig/tests/warn_changed_input/expected_stderr

@@ -0,0 +1,4 @@
+warning: user-provided values changed by Kconfig:
+  CONFIG_A: y -> n
+  CONFIG_NUM: 30 -> 20
+  CONFIG_DUP: y -> n

scripts/mod/modpost.c

@@ -969,7 +969,7 @@ static int secref_whitelist(const char *fromsec, const char *fromsym,
 	/* symbols in data sections that may refer to any init/exit sections */
 	if (match(fromsec, PATTERNS(DATA_SECTIONS)) &&
 	    match(tosec, PATTERNS(ALL_INIT_SECTIONS, ALL_EXIT_SECTIONS)) &&
-	    match(fromsym, PATTERNS("*_ops", "*_console")))
+	    match(fromsym, PATTERNS("*_ops", "*_ops.llvm.*", "*_console")))
 		return 0;
 
 	/* Check for pattern 3 */