Preprocessor+Linker Voodoo for boot param decl

include/bootparam.h

@@ -1,7 +1,24 @@
 #ifndef KARLOS_BOOTPARAM_H
 #define KARLOS_BOOTPARAM_H
 
-void bootparam_reset_values(void);
+#define BOOTPARAM_(name_, symbol) const struct bootparam_spec _bootparam_spec_ ## symbol __attribute__((section(".rodata.bootparam"))) = { name_, &symbol };
+
+#define BOOTPARAM_STRING(name_, symbol) BOOTPARAM_("S" name_, symbol)
+#define BOOTPARAM_BOOL(  name_, symbol) BOOTPARAM_("B" name_, symbol)
+#define BOOTPARAM_INT(   name_, symbol) BOOTPARAM_("I" name_, symbol)
+
+#define BOOTPARAM_TYPE_STRING 'S'
+#define BOOTPARAM_TYPE_BOOL   'B'
+#define BOOTPARAM_TYPE_INT    'I'
+
+// HACK: GCC seems to align global variables to multiples of 16.
+// Since we want to iterate over the .rodata.bootparam section,
+// the size of this struct needs to be a multiple of 16.
+struct bootparam_spec {
+	const char *name; // First byte encodes type
+	void       *var;
+};
+
 void bootparam_parse_config(char *text);
 
 #endif

kernel.ld

@@ -47,6 +47,9 @@ SECTIONS
         KEEP(*(.text.boot)) *(.text .text.*)   /* code */
     } : text
     .data : {
+        _bootparam_start = .;
+        *(.rodata.bootparam)
+        _bootparam_end = .;
         *(.rodata .rodata.*)                   /* data */
         *(.data .data.*)
     } : text

src/bootparam.c

@@ -1,41 +1,14 @@
 #include <std.h>
 #include <bootparam.h>
 
-enum bootparam_type {
-	BOOTPARAM_TYPE_INT,
-	BOOTPARAM_TYPE_BOOL,
-	BOOTPARAM_TYPE_STRING,
-};
+const char *_bootparam_bb_kernel;
+const char *_bootparam_bb_screen;
 
-union bootparam_value {
-	int64_t     i;
-	bool        b;
-	const char *s;
-};
+BOOTPARAM_STRING("kernel", _bootparam_bb_kernel);
+BOOTPARAM_STRING("screen", _bootparam_bb_screen);
 
-struct bootparam_spec {
-	enum bootparam_type   type;
-	union bootparam_value defval;
-	const char        *name;
-	void              *var;
-};
-
-extern bool ram_enable_logging;
-
-const struct bootparam_spec bootparam_specs[] = {
-	{
-		.name = "screen",
-		.type = BOOTPARAM_TYPE_STRING,
-		.defval = { .s = "800x600" },
-		.var = NULL,
-	},
-	{
-		.name = "ram.enable_logging",
-		.type = BOOTPARAM_TYPE_BOOL,
-		.defval = { .b = false },
-		.var = &ram_enable_logging,
-	},
-};
+extern const struct bootparam_spec _bootparam_start[];
+extern const struct bootparam_spec _bootparam_end[];
 
 static bool
 is_space_char(char c)
@@ -55,9 +28,8 @@ parse_bootparam_value(unsigned lineno, char *key, char *val)
 	(void)lineno;
 
 	const struct bootparam_spec *spec = NULL;
-	for (unsigned i = 0; i < sizeof(bootparam_specs) / sizeof(bootparam_specs[0]); i++) {
-		const struct bootparam_spec *s = &bootparam_specs[i];
-		if (streq(key, s->name)) {
+	for (const struct bootparam_spec *s = _bootparam_start; s < _bootparam_end; s++) {
+		if (streq(key, s->name+1)) {
 			spec = s;
 			break;
 		}
@@ -72,7 +44,7 @@ parse_bootparam_value(unsigned lineno, char *key, char *val)
 		return;
 	}
 
-	switch (spec->type) {
+	switch (spec->name[0]) {
 	case BOOTPARAM_TYPE_STRING:
 		*(const char **)spec->var = val;
 		break;
@@ -219,25 +191,3 @@ bootparam_parse_config(char *text)
 		lineno++;
 	}
 }
-
-void
-bootparam_reset_values(void)
-{
-	for (unsigned i = 0; i < sizeof(bootparam_specs) / sizeof (bootparam_specs[0]); i++) {
-		const struct bootparam_spec *s = &bootparam_specs[i];
-		if (!s->var) {
-			continue;
-		}
-		switch (s->type) {
-		case BOOTPARAM_TYPE_STRING:
-			*(const char **)s->var = s->defval.s;
-			break;
-		case BOOTPARAM_TYPE_BOOL:
-			*(bool *)s->var = s->defval.b;
-			break;
-		case BOOTPARAM_TYPE_INT:
-			*(int64_t *)s->var = s->defval.i;
-			break;
-		}
-	}
-}

src/kernel.c

@@ -38,7 +38,6 @@ void _start() {
     __get_cpuid(0x1, &info[0], &info[1], &info[2], &info[3]);
     unsigned procid = info[1] >> 24;
     if (procid == bootboot.bspid) {
-        bootparam_reset_values();
         bootparam_parse_config(environment);
         cpu_init_bsp();
     } else {

src/ram.c

@@ -3,6 +3,7 @@
 #include "ram.h"
 #include "bootboot.h"
 #include "mem_range.h"
+#include "bootparam.h"
 
 extern BOOTBOOT bootboot;
 
@@ -30,7 +31,9 @@ bool ram_initialized = false;
 #define CHECK_INIT do { } while (0)
 #endif
 
-bool ram_enable_logging;
+bool ram_enable_logging = false;
+
+BOOTPARAM_BOOL("ram.enable_logging", ram_enable_logging);
 
 
 size_t frame_size_to_num_bytes(enum frame_size size) {