linux-kernel - [RFC PATCH v2 02/10] tools/nolibc: crt: Split _start

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Message-ID: <20260204124542.523567-3-daniel@thingy.jp>
Date: Wed,  4 Feb 2026 21:45:34 +0900
From: Daniel Palmer <daniel@...ngy.jp>
To: w@....eu,
	linux@...ssschuh.net
Cc: linux-kernel@...r.kernel.org,
	Daniel Palmer <daniel@...ngy.jp>
Subject: [RFC PATCH v2 02/10] tools/nolibc: crt: Split _start_c() into stack-only and normal parts

To prepare for nolibc programs being able to relocate themselves
we need to split _start_c() into two parts:

- One part that only uses the stack so there are no accesses via
  the GOT etc that isn't setup yet. Note that on m68k at least
  this also means forcing the stackprotector off because accessing
  the stack protector canary is done via the GOT.

- Another part that is called after we have done relocation so it
  is safe to access global variables etc that might use the GOT etc.

Signed-off-by: Daniel Palmer <daniel@...ngy.jp>
---
 tools/include/nolibc/compiler.h |  6 ++++
 tools/include/nolibc/crt.h      | 57 ++++++++++++++++++---------------
 2 files changed, 38 insertions(+), 25 deletions(-)

diff --git a/tools/include/nolibc/compiler.h b/tools/include/nolibc/compiler.h
index 87090bbc53e0..3f403e54e4f4 100644
--- a/tools/include/nolibc/compiler.h
+++ b/tools/include/nolibc/compiler.h
@@ -47,4 +47,10 @@
 #  define __nolibc_fallthrough do { } while (0)
 #endif /* __nolibc_has_attribute(fallthrough) */
 
+#if __nolibc_has_feature(undefined_behavior_sanitizer)
+#  define __no_sanitize __attribute__((no_sanitize("function")))
+#else
+#  define __no_sanitize
+#endif
+
 #endif /* _NOLIBC_COMPILER_H */
diff --git a/tools/include/nolibc/crt.h b/tools/include/nolibc/crt.h
index d9262998dae9..fab042f1ff62 100644
--- a/tools/include/nolibc/crt.h
+++ b/tools/include/nolibc/crt.h
@@ -27,26 +27,45 @@ extern void (*const __init_array_end[])(int, char **, char**) __attribute__((wea
 extern void (*const __fini_array_start[])(void) __attribute__((weak));
 extern void (*const __fini_array_end[])(void) __attribute__((weak));
 
-void _start_c(long *sp);
-__attribute__((weak,used))
-#if __nolibc_has_feature(undefined_behavior_sanitizer)
-	__attribute__((no_sanitize("function")))
-#endif
-void _start_c(long *sp)
+void _start_c_global_data(long argc, char **argv, char **envp, const unsigned long *auxv);
+__attribute__((weak, used))
+void __no_sanitize __no_stack_protector _start_c_global_data(long argc, char **argv, char **envp, const unsigned long *auxv)
 {
-	long argc;
-	char **argv;
-	char **envp;
-	int exitcode;
 	void (* const *ctor_func)(int, char **, char **);
 	void (* const *dtor_func)(void);
-	const unsigned long *auxv;
 	/* silence potential warning: conflicting types for 'main' */
 	int _nolibc_main(int, char **, char **) __asm__ ("main");
+	int exitcode;
 
 	/* initialize stack protector */
 	__stack_chk_init();
 
+	environ = envp;
+	_auxv = auxv;
+
+	for (ctor_func = __preinit_array_start; ctor_func < __preinit_array_end; ctor_func++)
+		(*ctor_func)(argc, argv, envp);
+	for (ctor_func = __init_array_start; ctor_func < __init_array_end; ctor_func++)
+		(*ctor_func)(argc, argv, envp);
+
+	/* go to application */
+	exitcode = _nolibc_main(argc, argv, envp);
+
+	for (dtor_func = __fini_array_end; dtor_func > __fini_array_start;)
+		(*--dtor_func)();
+
+	exit(exitcode);
+}
+
+void _start_c(long *sp);
+__attribute__((weak, used))
+void __no_sanitize __no_stack_protector _start_c(long *sp)
+{
+	long argc;
+	char **argv;
+	char **envp;
+	const unsigned long *auxv;
+
 	/*
 	 * sp  :    argc          <-- argument count, required by main()
 	 * argv:    argv[0]       <-- argument vector, required by main()
@@ -69,25 +88,13 @@ void _start_c(long *sp)
 	argv = (void *)(sp + 1);
 
 	/* find environ */
-	environ = envp = argv + argc + 1;
+	envp = argv + argc + 1;
 
 	/* find _auxv */
 	for (auxv = (void *)envp; *auxv++;)
 		;
-	_auxv = auxv;
 
-	for (ctor_func = __preinit_array_start; ctor_func < __preinit_array_end; ctor_func++)
-		(*ctor_func)(argc, argv, envp);
-	for (ctor_func = __init_array_start; ctor_func < __init_array_end; ctor_func++)
-		(*ctor_func)(argc, argv, envp);
-
-	/* go to application */
-	exitcode = _nolibc_main(argc, argv, envp);
-
-	for (dtor_func = __fini_array_end; dtor_func > __fini_array_start;)
-		(*--dtor_func)();
-
-	exit(exitcode);
+	_start_c_global_data(argc, argv, envp, auxv);
 }
 
 #endif /* NOLIBC_NO_RUNTIME */
-- 
2.51.0