Kbuild fixes for v6.14

- Suppress false-positive -Wformat-{overflow,truncation}-non-kprintf
    warnings regardless of the W= option
 
  - Avoid CONFIG_TRIM_UNUSED_KSYMS dropping symbols passed to symbol_get()
 
  - Fix a build regression of the Debian linux-headers package
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Merge tag 'kbuild-fixes-v6.14' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild

Pull Kbuild fixes from Masahiro Yamada:

 - Suppress false-positive -Wformat-{overflow,truncation}-non-kprintf
   warnings regardless of the W= option

 - Avoid CONFIG_TRIM_UNUSED_KSYMS dropping symbols passed to symbol_get()

 - Fix a build regression of the Debian linux-headers package

* tag 'kbuild-fixes-v6.14' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild:
  kbuild: install-extmod-build: add missing quotation marks for CC variable
  kbuild: fix misspelling in scripts/Makefile.lib
  kbuild: keep symbols for symbol_get() even with CONFIG_TRIM_UNUSED_KSYMS
  scripts/Makefile.extrawarn: Do not show clang's non-kprintf warnings at W=1

include/asm-generic/vmlinux.lds.h

@@ -1038,6 +1038,7 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
 	*(.discard)							\
 	*(.discard.*)							\
 	*(.export_symbol)						\
+	*(.no_trim_symbol)						\
 	*(.modinfo)							\
 	/* ld.bfd warns about .gnu.version* even when not emitted */	\
 	*(.gnu.version*)						\

include/linux/module.h

@@ -306,7 +306,10 @@ extern int modules_disabled; /* for sysctl */
 /* Get/put a kernel symbol (calls must be symmetric) */
 void *__symbol_get(const char *symbol);
 void *__symbol_get_gpl(const char *symbol);
-#define symbol_get(x) ((typeof(&x))(__symbol_get(__stringify(x))))
+#define symbol_get(x)	({ \
+	static const char __notrim[] \
+		__used __section(".no_trim_symbol") = __stringify(x); \
+	(typeof(&x))(__symbol_get(__stringify(x))); })
 
 /* modules using other modules: kdb wants to see this. */
 struct module_use {

scripts/Makefile.extrawarn

@@ -31,6 +31,11 @@ KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds
 ifdef CONFIG_CC_IS_CLANG
 # The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable.
 KBUILD_CFLAGS += -Wno-gnu
+
+# Clang checks for overflow/truncation with '%p', while GCC does not:
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219
+KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow-non-kprintf)
+KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation-non-kprintf)
 else
 
 # gcc inanely warns about local variables called 'main'
@@ -105,11 +110,6 @@ KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
 KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow)
 ifdef CONFIG_CC_IS_GCC
 KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation)
-else
-# Clang checks for overflow/truncation with '%p', while GCC does not:
-# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219
-KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow-non-kprintf)
-KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation-non-kprintf)
 endif
 KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)
 

scripts/Makefile.lib

@@ -305,7 +305,7 @@ endef
 # These are shared by some Makefile.* files.
 
 ifdef CONFIG_LTO_CLANG
-# Run $(LD) here to covert LLVM IR to ELF in the following cases:
+# Run $(LD) here to convert LLVM IR to ELF in the following cases:
 #  - when this object needs objtool processing, as objtool cannot process LLVM IR
 #  - when this is a single-object module, as modpost cannot process LLVM IR
 cmd_ld_single = $(if $(objtool-enabled)$(is-single-obj-m), ; $(LD) $(ld_flags) -r -o $(tmp-target) $@; mv $(tmp-target) $@)

scripts/mod/modpost.c

@@ -507,6 +507,9 @@ static int parse_elf(struct elf_info *info, const char *filename)
 			info->modinfo_len = sechdrs[i].sh_size;
 		} else if (!strcmp(secname, ".export_symbol")) {
 			info->export_symbol_secndx = i;
+		} else if (!strcmp(secname, ".no_trim_symbol")) {
+			info->no_trim_symbol = (void *)hdr + sechdrs[i].sh_offset;
+			info->no_trim_symbol_len = sechdrs[i].sh_size;
 		}
 
 		if (sechdrs[i].sh_type == SHT_SYMTAB) {
@@ -1566,6 +1569,14 @@ static void read_symbols(const char *modname)
 	/* strip trailing .o */
 	mod = new_module(modname, strlen(modname) - strlen(".o"));
 
+	/* save .no_trim_symbol section for later use */
+	if (info.no_trim_symbol_len) {
+		mod->no_trim_symbol = xmalloc(info.no_trim_symbol_len);
+		memcpy(mod->no_trim_symbol, info.no_trim_symbol,
+		       info.no_trim_symbol_len);
+		mod->no_trim_symbol_len = info.no_trim_symbol_len;
+	}
+
 	if (!mod->is_vmlinux) {
 		license = get_modinfo(&info, "license");
 		if (!license)
@@ -1728,6 +1739,28 @@ static void handle_white_list_exports(const char *white_list)
 	free(buf);
 }
 
+/*
+ * Keep symbols recorded in the .no_trim_symbol section. This is necessary to
+ * prevent CONFIG_TRIM_UNUSED_KSYMS from dropping EXPORT_SYMBOL because
+ * symbol_get() relies on the symbol being present in the ksymtab for lookups.
+ */
+static void keep_no_trim_symbols(struct module *mod)
+{
+	unsigned long size = mod->no_trim_symbol_len;
+
+	for (char *s = mod->no_trim_symbol; s; s = next_string(s , &size)) {
+		struct symbol *sym;
+
+		/*
+		 * If find_symbol() returns NULL, this symbol is not provided
+		 * by any module, and symbol_get() will fail.
+		 */
+		sym = find_symbol(s);
+		if (sym)
+			sym->used = true;
+	}
+}
+
 static void check_modname_len(struct module *mod)
 {
 	const char *mod_name;
@@ -2254,6 +2287,8 @@ int main(int argc, char **argv)
 		read_symbols_from_files(files_source);
 
 	list_for_each_entry(mod, &modules, list) {
+		keep_no_trim_symbols(mod);
+
 		if (mod->dump_file || mod->is_vmlinux)
 			continue;
 

scripts/mod/modpost.h

@@ -111,6 +111,8 @@ struct module_alias {
  *
  * @dump_file: path to the .symvers file if loaded from a file
  * @aliases: list head for module_aliases
+ * @no_trim_symbol: .no_trim_symbol section data
+ * @no_trim_symbol_len: length of the .no_trim_symbol section
  */
 struct module {
 	struct list_head list;
@@ -128,6 +130,8 @@ struct module {
 	// Actual imported namespaces
 	struct list_head imported_namespaces;
 	struct list_head aliases;
+	char *no_trim_symbol;
+	unsigned int no_trim_symbol_len;
 	char name[];
 };
 
@@ -141,6 +145,8 @@ struct elf_info {
 	char         *strtab;
 	char	     *modinfo;
 	unsigned int modinfo_len;
+	char         *no_trim_symbol;
+	unsigned int no_trim_symbol_len;
 
 	/* support for 32bit section numbers */
 

scripts/module.lds.S

@@ -16,6 +16,7 @@ SECTIONS {
 		*(.discard)
 		*(.discard.*)
 		*(.export_symbol)
+		*(.no_trim_symbol)
 	}
 
 	__ksymtab		0 : ALIGN(8) { *(SORT(___ksymtab+*)) }

scripts/package/install-extmod-build

@@ -63,7 +63,7 @@ if [ "${CC}" != "${HOSTCC}" ]; then
 	# Clear VPATH and srcroot because the source files reside in the output
 	# directory.
 	# shellcheck disable=SC2016 # $(MAKE), $(CC), and $(build) will be expanded by Make
-	"${MAKE}" run-command KBUILD_RUN_COMMAND='+$(MAKE) HOSTCC=$(CC) VPATH= srcroot=. $(build)='"${destdir}"/scripts
+	"${MAKE}" run-command KBUILD_RUN_COMMAND='+$(MAKE) HOSTCC="$(CC)" VPATH= srcroot=. $(build)='"${destdir}"/scripts
 
 	rm -f "${destdir}/scripts/Kbuild"
 fi