tools/nolibc: add option to disable runtime

In principle, it is possible to use nolibc for only some object files in
a program. In that case, the startup code in _start and _start_c is not
going to be used. Add the NOLIBC_NO_RUNTIME compile time option to
disable it entirely and also remove anything that depends on it.

Doing this avoids warnings from modpost for UML as the _start_c code
references the main function from the .init.text section while it is not
inside .init itself.

Signed-off-by: Benjamin Berg <[e-mail]>
Signed-off-by: Thomas Weißschuh <[e-mail]>

tools/include/nolibc/arch-arm.h

···
 	_arg1;                                                                \
 })
 
+#ifndef NOLIBC_NO_RUNTIME
 /* startup code */
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
···
 	);
 	__nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_RUNTIME */
 
 #endif /* _NOLIBC_ARCH_ARM_H */

tools/include/nolibc/arch-arm64.h

···
 	_arg1;                                                                \
 })
 
+#ifndef NOLIBC_NO_RUNTIME
 /* startup code */
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
···
 	);
 	__nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_RUNTIME */
 #endif /* _NOLIBC_ARCH_ARM64_H */

tools/include/nolibc/arch-loongarch.h

···
 	_arg1;                                                                \
 })
 
+#ifndef NOLIBC_NO_RUNTIME
 /* startup code */
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
···
 	);
 	__nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_RUNTIME */
 
 #endif /* _NOLIBC_ARCH_LOONGARCH_H */

tools/include/nolibc/arch-m68k.h

···
 	_num;                                                                 \
 })
 
+#ifndef NOLIBC_NO_RUNTIME
 void _start(void);
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
···
 	);
 	__nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_RUNTIME */
 
 #endif /* _NOLIBC_ARCH_M68K_H */

tools/include/nolibc/arch-mips.h

···
 
 #endif /* _ABIO32 */
 
+#ifndef NOLIBC_NO_RUNTIME
 /* startup code, note that it's called __start on MIPS */
 void __start(void);
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector __start(void)
···
 	);
 	__nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_RUNTIME */
 
 #endif /* _NOLIBC_ARCH_MIPS_H */

tools/include/nolibc/arch-powerpc.h

···
 #endif
 #endif /* !__powerpc64__ */
 
+#ifndef NOLIBC_NO_RUNTIME
 /* startup code */
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
···
 #endif
 	__nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_RUNTIME */
 
 #endif /* _NOLIBC_ARCH_POWERPC_H */

tools/include/nolibc/arch-riscv.h

···
 	_arg1;                                                                \
 })
 
+#ifndef NOLIBC_NO_RUNTIME
 /* startup code */
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
···
 	);
 	__nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_RUNTIME */
 
 #endif /* _NOLIBC_ARCH_RISCV_H */

tools/include/nolibc/arch-s390.h

···
 	_arg1;								\
 })
 
+#ifndef NOLIBC_NO_RUNTIME
 /* startup code */
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
···
 	);
 	__nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_RUNTIME */
 
 struct s390_mmap_arg_struct {
 	unsigned long addr;

tools/include/nolibc/arch-sh.h

···
 	_ret;                                                                 \
 })
 
+#ifndef NOLIBC_NO_RUNTIME
 /* startup code */
 void _start_wrapper(void);
 void __attribute__((weak,noreturn)) __nolibc_entrypoint __no_stack_protector _start_wrapper(void)
···
 	);
 	__nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_RUNTIME */
 
 #endif /* _NOLIBC_ARCH_SH_H */

tools/include/nolibc/arch-sparc.h

···
 	_arg1;                                                                \
 })
 
+#ifndef NOLIBC_NO_RUNTIME
 /* startup code */
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
···
 	);
 	__nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_RUNTIME */
 
 static pid_t getpid(void);
 

tools/include/nolibc/arch-x86.h

···
 	_eax;							\
 })
 
+#ifndef NOLIBC_NO_RUNTIME
 /* startup code */
 /*
  * i386 System V ABI mandates:
···
 	);
 	__nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_RUNTIME */
 
 #else /* !defined(__x86_64__) */
 
···
 	_ret;                                                                 \
 })
 
+#ifndef NOLIBC_NO_RUNTIME
 /* startup code */
 /*
  * x86-64 System V ABI mandates:
···
 	);
 	__nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_RUNTIME */
 
 #define NOLIBC_ARCH_HAS_MEMMOVE
 void *memmove(void *dst, const void *src, size_t len);

tools/include/nolibc/crt.h

···
 #ifndef _NOLIBC_CRT_H
 #define _NOLIBC_CRT_H
 
+#ifndef NOLIBC_NO_RUNTIME
+
 #include "compiler.h"
 
 char **environ __attribute__((weak));
···
 	exit(exitcode);
 }
 
+#endif /* NOLIBC_NO_RUNTIME */
 #endif /* _NOLIBC_CRT_H */

tools/include/nolibc/stackprotector.h

···
 
 #include "compiler.h"
 
+#ifndef NOLIBC_NO_RUNTIME
 #if defined(_NOLIBC_STACKPROTECTOR)
 
 #include "sys.h"
···
 #else /* !defined(_NOLIBC_STACKPROTECTOR) */
 static void __stack_chk_init(void) {}
 #endif /* defined(_NOLIBC_STACKPROTECTOR) */
+#endif /* NOLIBC_NO_RUNTIME */
 
 #endif /* _NOLIBC_STACKPROTECTOR_H */

tools/include/nolibc/stdlib.h

···
 	munmap(heap, heap->len);
 }
 
+#ifndef NOLIBC_NO_RUNTIME
 /* getenv() tries to find the environment variable named <name> in the
  * environment array pointed to by global variable "environ" which must be
  * declared as a char **, and must be terminated by a NULL (it is recommended
···
 	}
 	return NULL;
 }
+#endif /* NOLIBC_NO_RUNTIME */
 
 static __attribute__((unused))
 void *malloc(size_t len)

tools/include/nolibc/sys.h

···
 	return sys_gettid();
 }
 
+#ifndef NOLIBC_NO_RUNTIME
 static unsigned long getauxval(unsigned long key);
 
 /*
···
 {
 	return __sysret((int)getauxval(AT_PAGESZ) ?: -ENOENT);
 }
-
+#endif /* NOLIBC_NO_RUNTIME */
 
 /*
  * uid_t getuid(void);

tools/include/nolibc/sys/auxv.h

···
 #ifndef _NOLIBC_SYS_AUXV_H
 #define _NOLIBC_SYS_AUXV_H
 
+#ifndef NOLIBC_NO_RUNTIME
+
 #include "../crt.h"
 
 static __attribute__((unused))
···
 	return ret;
 }
 
+#endif /* NOLIBC_NO_RUNTIME */
 #endif /* _NOLIBC_SYS_AUXV_H */