tools/nolibc: add support for constructors and destructors

With the startup code moved to C, implementing support for
constructors and deconstructors is fairly easy to implement.

Examples for code size impact:

   text	   data	    bss	    dec	    hex	filename
  21837	    104	     88	  22029	   560d	nolibc-test.before
  22135	    120	     88	  22343	   5747	nolibc-test.after
  21970	    104	     88	  22162	   5692 nolibc-test.after-only-crt.h-changes

The sections are defined by [0].

[0] https://refspecs.linuxfoundation.org/elf/gabi4+/ch5.dynamic.html

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/lkml/20231007-nolibc-constructors-v2-1-ef84693efbc1@weissschuh.net/

diff --git a/tools/include/nolibc/crt.h b/tools/include/nolibc/crt.h
index a05655b4ce1d7f132c0ae782ec47df9bb077f5ac..43b551468c2a85ecdf6f830d0ed9d9b390326917 100644 (file)
--- a/tools/include/nolibc/crt.h
+++ b/tools/include/nolibc/crt.h
@@ -13,12 +13,23 @@ const unsigned long *_auxv __attribute__((weak));
 static void __stack_chk_init(void);
 static void exit(int);
 
+extern void (*const __preinit_array_start[])(void) __attribute__((weak));
+extern void (*const __preinit_array_end[])(void) __attribute__((weak));
+
+extern void (*const __init_array_start[])(void) __attribute__((weak));
+extern void (*const __init_array_end[])(void) __attribute__((weak));
+
+extern void (*const __fini_array_start[])(void) __attribute__((weak));
+extern void (*const __fini_array_end[])(void) __attribute__((weak));
+
 __attribute__((weak))
 void _start_c(long *sp)
 {
        long argc;
        char **argv;
        char **envp;
+       int exitcode;
+       void (* const *func)(void);
        const unsigned long *auxv;
        /* silence potential warning: conflicting types for 'main' */
        int _nolibc_main(int, char **, char **) __asm__ ("main");
@@ -55,8 +66,18 @@ void _start_c(long *sp)
                ;
        _auxv = auxv;
 
+       for (func = __preinit_array_start; func < __preinit_array_end; func++)
+               (*func)();
+       for (func = __init_array_start; func < __init_array_end; func++)
+               (*func)();
+
        /* go to application */
-       exit(_nolibc_main(argc, argv, envp));
+       exitcode = _nolibc_main(argc, argv, envp);
+
+       for (func = __fini_array_end; func > __fini_array_start;)
+               (*--func)();
+
+       exit(exitcode);
 }
 
 #endif /* _NOLIBC_CRT_H */

diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 7e3936c182dc7e823994f3e02abd7011cf85a183..8da7f15d010e1a9016c937bde07b1b9210aad48b 100644 (file)
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -57,6 +57,9 @@ static int test_argc;
 /* will be used by some test cases as readable file, please don't write it */
 static const char *argv0;
 
+/* will be used by constructor tests */
+static int constructor_test_value;
+
 /* definition of a series of tests */
 struct test {
        const char *name;              /* test name */
@@ -594,6 +597,19 @@ int expect_strne(const char *expr, int llen, const char *cmp)
 #define CASE_TEST(name) \
        case __LINE__: llen += printf("%d %s", test, #name);
 
+/* constructors validate that they are executed in definition order */
+__attribute__((constructor))
+static void constructor1(void)
+{
+       constructor_test_value = 1;
+}
+
+__attribute__((constructor))
+static void constructor2(void)
+{
+       constructor_test_value *= 2;
+}
+
 int run_startup(int min, int max)
 {
        int test;
@@ -630,6 +646,7 @@ int run_startup(int min, int max)
                CASE_TEST(environ_HOME);     EXPECT_PTRNZ(1, getenv("HOME")); break;
                CASE_TEST(auxv_addr);        EXPECT_PTRGT(test_auxv != (void *)-1, test_auxv, brk); break;
                CASE_TEST(auxv_AT_UID);      EXPECT_EQ(1, getauxval(AT_UID), getuid()); break;
+               CASE_TEST(constructor);      EXPECT_EQ(1, constructor_test_value, 2); break;
                case __LINE__:
                        return ret; /* must be last */
                /* note: do not set any defaults so as to permit holes above */