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 --- Changes in v2: - Drop RFC status. - Add comment to constructor test that execution in definition-order is expected. (Willy) - Rework destructor loop to avoid underflow if __fini_array_end is not provided by the linker. - Link to v1: https://lore.kernel.org/r/20231005-nolibc-constructors-v1-1-776d56bbe917@wei... --- tools/include/nolibc/crt.h | 23 ++++++++++++++++++++++- tools/testing/selftests/nolibc/nolibc-test.c | 17 +++++++++++++++++ 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/tools/include/nolibc/crt.h b/tools/include/nolibc/crt.h index a5f33fef1672..b84f5fbb7b58 100644 --- a/tools/include/nolibc/crt.h +++ b/tools/include/nolibc/crt.h @@ -13,11 +13,22 @@ 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)); + 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"); @@ -54,8 +65,18 @@ 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 a3ee4496bf0a..88ea8e06e596 100644 --- 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; @@ -631,6 +647,7 @@ int run_startup(int min, int max) 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(auxv_AT_PAGESZ); EXPECT_GE(1, getauxval(AT_PAGESZ), 4096); 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 */

--- base-commit: ab663cc32912914258bc8a2fbd0e753f552ee9d8 change-id: 20231005-nolibc-constructors-b2aebffe9b65

Best regards,