Use @file to pass the --cfg flags to rustc (fixes #22)

It also helps to avoid spamming the terminal when doing verbose builds.

Signed-off-by: Finn Behrens <me@kloenk.de>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: kloenk

Makefile

@@ -726,7 +726,7 @@ $(KCONFIG_CONFIG):
 # This exploits the 'multi-target pattern rule' trick.
 # The syncconfig should be executed only once to make all the targets.
 # (Note: use the grouped target '&:' when we bump to GNU Make 4.3)
-%/config/auto.conf %/config/auto.conf.cmd %/generated/autoconf.h: $(KCONFIG_CONFIG)
+%/config/auto.conf %/config/auto.conf.cmd %/generated/autoconf.h %/generated/rustc_cfg: $(KCONFIG_CONFIG)
 	$(Q)$(MAKE) -f $(srctree)/Makefile syncconfig
 else # !may-sync-config
 # External modules and some install targets need include/generated/autoconf.h

scripts/Makefile.lib

@@ -229,9 +229,9 @@ c_flags        = -Wp,-MMD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
 RUST_BINDGEN_CFLAGS = $(c_flags) $(KBUILD_CFLAGS_MODULE)
 export RUST_BINDGEN_CFLAGS
 
-rustc_cfg_flags = $(shell sed -nE 's/^(CONFIG_[^=]+)=(y|m)$$/--cfg \1/p' $(srctree)/include/config/auto.conf | xargs)
+KCONFIG_RUSTC_CFG ?= $(srctree)/include/generated/rustc_cfg
 
-rustc_flags     = $(_rustc_flags) $(modkern_rustcflags) $(rustc_cfg_flags)
+rustc_flags     = $(_rustc_flags) $(modkern_rustcflags) @$(shell readlink -f $(KCONFIG_RUSTC_CFG))
 
 # Passed by cargo
 RUSTFLAGS = $(rustc_flags)

scripts/kconfig/confdata.c

@@ -636,6 +636,56 @@ static struct conf_printer kconfig_printer_cb =
 	.print_comment = kconfig_print_comment,
 };
 
+/*
+ * rustc cfg printer
+ *
+ * This printer is used when generating the resulting rustc configuration
+ * after kconfig invocation and `defconfig` files.
+ */
+static void rustc_cfg_print_symbol(FILE *fp, struct symbol *sym, const char *value, void *arg)
+{
+	const char *str;
+
+	switch (sym->type) {
+	case S_INT:
+	case S_HEX:
+	case S_BOOLEAN:
+	case S_TRISTATE:
+		str = sym_escape_string_value(value);
+
+		/*
+		 * We don't care about disabled ones, i.e. no need for
+		 * what otherwise are "comments" in other printers.
+		 */
+		if (*value == 'n')
+			return;
+
+		/*
+		 * To have similar functionality to the C macro `IS_ENABLED()`,
+		 * from Rust, we provide an empty `--cfg CONFIG_X` here in
+		 * both `y` and `m` cases.
+		 *
+		 * Then, the common `fprintf()` below will also give us
+		 * a `--cfg CONFIG_X="y"` or `--cfg CONFIG_X="m"`, which can
+		 * be used as the equivalent of `IS_BUILTIN()`/`IS_MODULE()`.
+		 */
+		if (*value == 'y' || *value == 'm')
+			fprintf(fp, "--cfg=%s%s\n", CONFIG_, sym->name);
+
+		break;
+	default:
+		str = value;
+		break;
+	}
+
+	fprintf(fp, "--cfg=%s%s=%s\n", CONFIG_, sym->name, str);
+}
+
+static struct conf_printer rustc_cfg_printer_cb =
+{
+	.print_symbol = rustc_cfg_print_symbol,
+};
+
 /*
  * Header printer
  *
@@ -1043,7 +1093,7 @@ int conf_write_autoconf(int overwrite)
 	struct symbol *sym;
 	const char *name;
 	const char *autoconf_name = conf_get_autoconfig_name();
-	FILE *out, *out_h;
+	FILE *out, *out_h, *out_rustc_cfg;
 	int i;
 
 	if (!overwrite && is_present(autoconf_name))
@@ -1064,6 +1114,13 @@ int conf_write_autoconf(int overwrite)
 		return 1;
 	}
 
+	out_rustc_cfg = fopen(".tmp_rustc_cfg", "w");
+	if (!out_rustc_cfg) {
+		fclose(out);
+		fclose(out_h);
+		return 1;
+	}
+
 	conf_write_heading(out, &kconfig_printer_cb, NULL);
 	conf_write_heading(out_h, &header_printer_cb, NULL);
 
@@ -1075,9 +1132,11 @@ int conf_write_autoconf(int overwrite)
 		/* write symbols to auto.conf and autoconf.h */
 		conf_write_symbol(out, sym, &kconfig_printer_cb, (void *)1);
 		conf_write_symbol(out_h, sym, &header_printer_cb, NULL);
+		conf_write_symbol(out_rustc_cfg, sym, &rustc_cfg_printer_cb, NULL);
 	}
 	fclose(out);
 	fclose(out_h);
+	fclose(out_rustc_cfg);
 
 	name = getenv("KCONFIG_AUTOHEADER");
 	if (!name)
@@ -1096,6 +1155,14 @@ int conf_write_autoconf(int overwrite)
 	if (rename(".tmpconfig", autoconf_name))
 		return 1;
 
+	name = getenv("KCONFIG_RUSTC_CFG");
+	if (!name)
+		name = "include/generated/rustc_cfg";
+	if (make_parent_dir(name))
+		return 1;
+	if (rename(".tmp_rustc_cfg", name))
+		return 1;
+
 	return 0;
 }