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 <[email protected]>
---
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/[email protected]
---
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,
--
Thomas Weißschuh <[email protected]>
On Sat, Oct 07, 2023 at 12:01:39PM +0200, Thomas Wei?schuh wrote:
> 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 Wei?schuh <[email protected]>
Acked-by: Willy Tarreau <[email protected]>
Thanks!
Willy