Support for static constructors with priorities

Instead of relying on __attribute__((constructor)), use our own system
that should work everywhere -- regardless of the C standard library, or
the system supporting them.

As a bonus, each constructor now gets a pointer to a Lwan struct, making
it easier to install initialization hooks.

Author: lpereira

src/bin/tools/bin2hex.c

@@ -28,14 +28,6 @@
 
 #include "lwan-private.h"
 
-static int constructor_attr_supported = 0;
-
-LWAN_CONSTRUCTOR()
-static void initialize_constructor_attr_supported(void)
-{
-    constructor_attr_supported = 1;
-}
-
 static int bin2hex_mmap(const char *path, const char *identifier)
 {
     int fd = open(path, O_RDONLY | O_CLOEXEC);
@@ -104,15 +96,12 @@ static int bin2hex(const char *path, const char *identifier)
 
     printf("\n/* Contents of %s available through %s_value */\n", path, identifier);
 
-    if (constructor_attr_supported) {
-        printf("#if defined(__GNUC__) || defined(__clang__)\n");
-        r |= bin2hex_incbin(path, identifier);
-        printf("#else\n");
-        r |= bin2hex_mmap(path, identifier);
-        printf("#endif\n\n");
-    } else {
-        r |= bin2hex_mmap(path, identifier);
-    }
+    printf("#if defined(__GNUC__) || defined(__clang__)\n");
+    r |= bin2hex_incbin(path, identifier);
+    printf("#else\n");
+    r |= bin2hex_mmap(path, identifier);
+    printf("#endif\n\n");
+
     return r;
 }
 
@@ -133,7 +122,7 @@ int main(int argc, char *argv[])
 
     printf("/* Auto generated by %s, do not edit. */\n", argv[0]);
     printf("#pragma once\n\n");
-    printf("#include \"lwan.h\"\n");
+    printf("#include \"lwan-private.h\"\n");
 
     for (arg = 1; arg < argc; arg += 2) {
         const char *path = argv[arg];
@@ -146,21 +135,18 @@ int main(int argc, char *argv[])
         }
     }
 
-    if (constructor_attr_supported) {
-        printf("#if defined(__GNUC__) || defined(__clang__)\n");
-        printf("__attribute__((constructor (101))) static void\n");
-        printf("initialize_bin2hex_%016lx(void)\n", (uintptr_t)argv);
-        printf("{\n");
-        for (arg = 1; arg < argc; arg += 2) {
-            const char *identifier = argv[arg + 1];
-
-            printf("    %s_value = (struct lwan_value) {.value = (char *)%s_start, "
-                   ".len = (size_t)(%s_end - %s_start)};\n",
-                   identifier, identifier, identifier, identifier);
-        }
-        printf("}\n");
-        printf("#endif\n");
+    printf("#if defined(__GNUC__) || defined(__clang__)\n");
+    printf("LWAN_CONSTRUCTOR(bin2hex_%016lx, 0)\n", (uintptr_t)argv);
+    printf("{\n");
+    for (arg = 1; arg < argc; arg += 2) {
+        const char *identifier = argv[arg + 1];
+
+        printf("    %s_value = (struct lwan_value) {.value = (char *)%s_start, "
+               ".len = (size_t)(%s_end - %s_start)};\n",
+               identifier, identifier, identifier, identifier);
     }
+    printf("}\n");
+    printf("#endif\n");
 
     return 0;
 }

src/lib/hash.c

@@ -208,8 +208,7 @@ static inline unsigned int hash_int64_crc32(const void *keyptr)
 
 #endif
 
-LWAN_CONSTRUCTOR(65535)
-static void initialize_fnv1a_seed(void)
+LWAN_CONSTRUCTOR(fnv1a_seed, 65535)
 {
     uint8_t entropy[128];
 

src/lib/lwan-lua.c

@@ -425,9 +425,7 @@ static int luaopen_log(lua_State *L)
 DEFINE_ARRAY_TYPE(lwan_lua_method_array, luaL_reg)
 static struct lwan_lua_method_array lua_methods;
 
-LWAN_CONSTRUCTOR()
-__attribute__((no_sanitize_address))
-static void register_lua_methods(void)
+LWAN_CONSTRUCTOR(register_lua_methods, 0)
 {
     const struct lwan_lua_method_info *info;
     luaL_reg *r;

src/lib/lwan-private.h

@@ -28,11 +28,21 @@
 #define DEFAULT_BUFFER_SIZE 4096
 #define DEFAULT_HEADERS_SIZE 2048
 
-#if defined(__APPLE__)
-# define LWAN_CONSTRUCTOR(prio_)	__attribute__((constructor))
-#else
-# define LWAN_CONSTRUCTOR(prio_)	__attribute__((constructor(prio_)))
-#endif
+struct lwan_constructor_callback_info {
+    void (*func)(struct lwan *);
+    int prio;
+};
+
+#define LWAN_CONSTRUCTOR(name_, prio_)                                         \
+    __attribute__((no_sanitize_address)) static void lwan_constructor_##name_( \
+        struct lwan *l __attribute__((unused)));                               \
+    static const struct lwan_constructor_callback_info __attribute__((         \
+        used, section(LWAN_SECTION_NAME(                                       \
+                  lwan_constructor)))) lwan_constructor_info_##name_ = {       \
+        .func = lwan_constructor_##name_,                                      \
+        .prio = (prio_),                                                       \
+    };                                                                         \
+    static ALWAYS_INLINE void lwan_constructor_##name_(struct lwan *l)
 
 struct lwan_request_parser_helper {
     struct lwan_value *buffer; /* The whole request buffer */

src/lib/lwan-readahead.c

@@ -60,8 +60,7 @@ static pthread_t readahead_self;
 static long page_size = PAGE_SIZE;
 
 #ifdef _SC_PAGESIZE
-LWAN_CONSTRUCTOR()
-static void get_page_size(void)
+LWAN_CONSTRUCTOR(get_page_size, 0)
 {
     long ps = sysconf(_SC_PAGESIZE);
 

src/lib/lwan-request.c

@@ -1112,8 +1112,7 @@ get_temp_dir(void)
     return NULL;
 }
 
-LWAN_CONSTRUCTOR()
-static void initialize_temp_dir(void)
+LWAN_CONSTRUCTOR(initialize_temp_dir, 0)
 {
     temp_dir = get_temp_dir();
 }

src/lib/lwan-status.c

@@ -243,8 +243,7 @@ void lwan_syslog_status_out(
     lwan_strbuf_free(&buf);
 }
 
-LWAN_CONSTRUCTOR()
-static void register_lwan_to_syslog(void)
+LWAN_CONSTRUCTOR(register_lwan_to_syslog, 0)
 {
     openlog("lwan", LOG_NDELAY | LOG_PID | LOG_CONS, LOG_USER);
 }

src/lib/lwan.c

@@ -869,6 +869,39 @@ static char *dup_or_null(const char *s)
     return s ? strdup(s) : NULL;
 }
 
+DEFINE_ARRAY_TYPE(constructor_array, struct lwan_constructor_callback_info)
+
+static int constructor_sort(const void *a, const void *b)
+{
+    const struct lwan_constructor_callback_info *ca = a;
+    const struct lwan_constructor_callback_info *cb = b;
+    return (ca->prio < cb->prio) - (ca->prio > cb->prio);
+}
+
+__attribute__((no_sanitize_address)) static void
+call_constructors(struct lwan *l)
+{
+    struct constructor_array constructors;
+    const struct lwan_constructor_callback_info *iter;
+
+    constructor_array_init(&constructors);
+    LWAN_SECTION_FOREACH(lwan_constructor, iter)
+    {
+        struct lwan_constructor_callback_info *info =
+            constructor_array_append(&constructors);
+        if (!info)
+            lwan_status_critical("Could not append to constructor array");
+        *info = *iter;
+    }
+    constructor_array_sort(&constructors, constructor_sort);
+
+    LWAN_ARRAY_FOREACH (&constructors, iter) {
+        iter->func(l);
+    }
+
+    constructor_array_reset(&constructors);
+}
+
 void lwan_init_with_config(struct lwan *l, const struct lwan_config *config)
 {
     /* Load defaults */
@@ -883,6 +916,8 @@ void lwan_init_with_config(struct lwan *l, const struct lwan_config *config)
      * their initialization. */
     lwan_status_init(l);
 
+    call_constructors(l);
+
     /* These will only print debugging messages. Debug messages are always
      * printed if we're on a debug build, so the quiet setting will be
      * respected. */
@@ -975,8 +1010,7 @@ void lwan_main_loop(struct lwan *l)
 }
 
 #ifdef CLOCK_MONOTONIC_COARSE
-LWAN_CONSTRUCTOR()
-static void detect_fastest_monotonic_clock(void)
+LWAN_CONSTRUCTOR(detect_fastest_monotonic_clock, 0)
 {
     struct timespec ts;
 

src/samples/clock/blocks.c

@@ -176,7 +176,7 @@ static const struct fall *fall[] = {
 
 static int block_sizes[10];
 
-LWAN_CONSTRUCTOR() void calculate_block_sizes(void)
+LWAN_CONSTRUCTOR(calculate_block_sizes, 0)
 {
     for (int i = 0; i < 10; i++) {
         const struct fall *instr = fall[i];

src/samples/clock/main.c

@@ -245,7 +245,7 @@ static const struct lwan_var_descriptor index_desc[] = {
 
 static struct lwan_tpl *index_tpl;
 
-LWAN_CONSTRUCTOR() static void initialize_template(void)
+LWAN_CONSTRUCTOR(initialize_template, 0)
 {
     static const char index[] =
         "<html>\n"

src/samples/clock/xdaliclock.c

@@ -155,7 +155,7 @@ frame_from_pixmap(const unsigned char *bits, int width, int height)
     return frame;
 }
 
-LWAN_CONSTRUCTOR() static void initialize_numbers(void)
+LWAN_CONSTRUCTOR(initialize_numbers, 0)
 {
     const struct raw_number *raw = get_raw_numbers();