[v2] tools/nolibc: add support for constructors and destructors
Commit Message
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@weissschuh.net
---
tools/include/nolibc/crt.h | 23 ++++++++++++++++++++++-
tools/testing/selftests/nolibc/nolibc-test.c | 17 +++++++++++++++++
2 files changed, 39 insertions(+), 1 deletion(-)
---
base-commit: ab663cc32912914258bc8a2fbd0e753f552ee9d8
change-id: 20231005-nolibc-constructors-b2aebffe9b65
Best regards,
Comments
On Sat, Oct 07, 2023 at 12:01:39PM +0200, Thomas Weißschuh 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 Weißschuh <linux@weissschuh.net>
Acked-by: Willy Tarreau <w@1wt.eu>
Thanks!
Willy
@@ -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 */
@@ -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 */