[PATCH 6/9] tools/nolibc: add option to disable startup code

15 Sep 2025

From: Benjamin Berg benjamin.berg@intel.com
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_STARTCODE 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 benjamin.berg@intel.com
---
 tools/include/nolibc/arch-arm.h       | 2 ++
 tools/include/nolibc/arch-arm64.h     | 2 ++
 tools/include/nolibc/arch-loongarch.h | 2 ++
 tools/include/nolibc/arch-m68k.h      | 2 ++
 tools/include/nolibc/arch-mips.h      | 2 ++
 tools/include/nolibc/arch-powerpc.h   | 2 ++
 tools/include/nolibc/arch-riscv.h     | 2 ++
 tools/include/nolibc/arch-s390.h      | 2 ++
 tools/include/nolibc/arch-sh.h        | 2 ++
 tools/include/nolibc/arch-sparc.h     | 2 ++
 tools/include/nolibc/arch-x86.h       | 4 ++++
 tools/include/nolibc/crt.h            | 3 +++
 tools/include/nolibc/stackprotector.h | 2 ++
 tools/include/nolibc/stdlib.h         | 2 ++
 tools/include/nolibc/sys.h            | 3 ++-
 tools/include/nolibc/sys/auxv.h       | 3 +++
 16 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/tools/include/nolibc/arch-arm.h b/tools/include/nolibc/arch-arm.h
index 1f66e7e5a444..24ad348cc1e8 100644
--- a/tools/include/nolibc/arch-arm.h
+++ b/tools/include/nolibc/arch-arm.h
@@ -185,6 +185,7 @@
 })
/* startup code */
+#ifndef NOLIBC_NO_STARTCODE
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
    __asm__ volatile (
@@ -193,5 +194,6 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
    );
    __nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_STARTCODE */
#endif /* _NOLIBC_ARCH_ARM_H */
diff --git a/tools/include/nolibc/arch-arm64.h b/tools/include/nolibc/arch-arm64.h
index 02a3f74c8ec8..554ebb51c761 100644
--- a/tools/include/nolibc/arch-arm64.h
+++ b/tools/include/nolibc/arch-arm64.h
@@ -142,6 +142,7 @@
 })
/* startup code */
+#ifndef NOLIBC_NO_STARTCODE
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
    __asm__ volatile (
@@ -150,4 +151,5 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
    );
    __nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_STARTCODE */
 #endif /* _NOLIBC_ARCH_ARM64_H */
diff --git a/tools/include/nolibc/arch-loongarch.h b/tools/include/nolibc/arch-loongarch.h
index 5511705303ea..cf14f7bf4081 100644
--- a/tools/include/nolibc/arch-loongarch.h
+++ b/tools/include/nolibc/arch-loongarch.h
@@ -143,6 +143,7 @@
 })
/* startup code */
+#ifndef NOLIBC_NO_STARTCODE
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
    __asm__ volatile (
@@ -151,5 +152,6 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
    );
    __nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_STARTCODE */
#endif /* _NOLIBC_ARCH_LOONGARCH_H */
diff --git a/tools/include/nolibc/arch-m68k.h b/tools/include/nolibc/arch-m68k.h
index 6dac1845f298..dc0d48a10c14 100644
--- a/tools/include/nolibc/arch-m68k.h
+++ b/tools/include/nolibc/arch-m68k.h
@@ -128,6 +128,7 @@
    _num;                                                                 \
 })
+#ifndef NOLIBC_NO_STARTCODE
 void _start(void);
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
@@ -137,5 +138,6 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
    );
    __nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_STARTCODE */
#endif /* _NOLIBC_ARCH_M68K_H */
diff --git a/tools/include/nolibc/arch-mips.h b/tools/include/nolibc/arch-mips.h
index 0cbac63b249a..6c6a65a99029 100644
--- a/tools/include/nolibc/arch-mips.h
+++ b/tools/include/nolibc/arch-mips.h
@@ -246,6 +246,7 @@
 #endif /* _ABIO32 */
/* startup code, note that it's called __start on MIPS */
+#ifndef NOLIBC_NO_STARTCODE
 void __start(void);
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector __start(void)
 {
@@ -266,5 +267,6 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector __
    );
    __nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_STARTCODE */
#endif /* _NOLIBC_ARCH_MIPS_H */
diff --git a/tools/include/nolibc/arch-powerpc.h b/tools/include/nolibc/arch-powerpc.h
index 204564bbcd32..7a01278e569c 100644
--- a/tools/include/nolibc/arch-powerpc.h
+++ b/tools/include/nolibc/arch-powerpc.h
@@ -184,6 +184,7 @@
 #endif /* !__powerpc64__ */
/* startup code */
+#ifndef NOLIBC_NO_STARTCODE
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
 #ifdef __powerpc64__
@@ -215,5 +216,6 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
 #endif
    __nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_STARTCODE */
#endif /* _NOLIBC_ARCH_POWERPC_H */
diff --git a/tools/include/nolibc/arch-riscv.h b/tools/include/nolibc/arch-riscv.h
index 885383a86c38..12ca37b8d964 100644
--- a/tools/include/nolibc/arch-riscv.h
+++ b/tools/include/nolibc/arch-riscv.h
@@ -140,6 +140,7 @@
 })
/* startup code */
+#ifndef NOLIBC_NO_STARTCODE
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
    __asm__ volatile (
@@ -152,5 +153,6 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
    );
    __nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_STARTCODE */
#endif /* _NOLIBC_ARCH_RISCV_H */
diff --git a/tools/include/nolibc/arch-s390.h b/tools/include/nolibc/arch-s390.h
index df4c3cc713ac..fb0d312847b8 100644
--- a/tools/include/nolibc/arch-s390.h
+++ b/tools/include/nolibc/arch-s390.h
@@ -140,6 +140,7 @@
 })
/* startup code */
+#ifndef NOLIBC_NO_STARTCODE
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
    __asm__ volatile (
@@ -155,6 +156,7 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
    );
    __nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_STARTCODE */
struct s390_mmap_arg_struct {
    unsigned long addr;
diff --git a/tools/include/nolibc/arch-sh.h b/tools/include/nolibc/arch-sh.h
index a96b8914607e..038bf364aa27 100644
--- a/tools/include/nolibc/arch-sh.h
+++ b/tools/include/nolibc/arch-sh.h
@@ -141,6 +141,7 @@
 })
/* startup code */
+#ifndef NOLIBC_NO_STARTCODE
 void _start_wrapper(void);
 void __attribute__((weak,noreturn)) __nolibc_entrypoint __no_stack_protector _start_wrapper(void)
 {
@@ -158,5 +159,6 @@ void __attribute__((weak,noreturn)) __nolibc_entrypoint __no_stack_protector _st
    );
    __nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_STARTCODE */
#endif /* _NOLIBC_ARCH_SH_H */
diff --git a/tools/include/nolibc/arch-sparc.h b/tools/include/nolibc/arch-sparc.h
index ca420d843e25..062eae1fa92d 100644
--- a/tools/include/nolibc/arch-sparc.h
+++ b/tools/include/nolibc/arch-sparc.h
@@ -153,6 +153,7 @@
 })
/* startup code */
+#ifndef NOLIBC_NO_STARTCODE
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
    __asm__ volatile (
@@ -169,6 +170,7 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
    );
    __nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_STARTCODE */
static pid_t getpid(void);
diff --git a/tools/include/nolibc/arch-x86.h b/tools/include/nolibc/arch-x86.h
index d3efc0c3b8ad..b4981e99f0a0 100644
--- a/tools/include/nolibc/arch-x86.h
+++ b/tools/include/nolibc/arch-x86.h
@@ -164,6 +164,7 @@
  * 2) The deepest stack frame should be set to zero
  *
  */
+#ifndef NOLIBC_NO_STARTCODE
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
    __asm__ volatile (
@@ -176,6 +177,7 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
    );
    __nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_STARTCODE */
#else /* !defined(__x86_64__) */
@@ -330,6 +332,7 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
  * 2) The deepest stack frame should be zero (the %rbp).
  *
  */
+#ifndef NOLIBC_NO_STARTCODE
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
    __asm__ volatile (
@@ -340,6 +343,7 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
    );
    __nolibc_entrypoint_epilogue();
 }
+#endif /* NOLIBC_NO_STARTCODE */
#define NOLIBC_ARCH_HAS_MEMMOVE
 void *memmove(void *dst, const void *src, size_t len);
diff --git a/tools/include/nolibc/crt.h b/tools/include/nolibc/crt.h
index 961cfe777c35..d72e616eeec9 100644
--- a/tools/include/nolibc/crt.h
+++ b/tools/include/nolibc/crt.h
@@ -7,6 +7,8 @@
 #ifndef _NOLIBC_CRT_H
 #define _NOLIBC_CRT_H
+#ifndef NOLIBC_NO_STARTCODE
+
 #include "compiler.h"
char **environ __attribute__((weak));
@@ -88,4 +90,5 @@ void _start_c(long *sp)
    exit(exitcode);
 }
+#endif /* NOLIBC_NO_STARTCODE */
 #endif /* _NOLIBC_CRT_H */
diff --git a/tools/include/nolibc/stackprotector.h b/tools/include/nolibc/stackprotector.h
index c71a2c257177..3dd4d3e53ca6 100644
--- a/tools/include/nolibc/stackprotector.h
+++ b/tools/include/nolibc/stackprotector.h
@@ -9,6 +9,7 @@
#include "compiler.h"
+#ifndef NOLIBC_NO_STARTCODE
 #if defined(_NOLIBC_STACKPROTECTOR)
#include "sys.h"
@@ -49,5 +50,6 @@ static __no_stack_protector void __stack_chk_init(void)
 #else /* !defined(_NOLIBC_STACKPROTECTOR) */
 static void __stack_chk_init(void) {}
 #endif /* defined(_NOLIBC_STACKPROTECTOR) */
+#endif /* NOLIBC_NO_STARTCODE */
#endif /* _NOLIBC_STACKPROTECTOR_H */
diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h
index 5fd99a480f82..ed12c9119aab 100644
--- a/tools/include/nolibc/stdlib.h
+++ b/tools/include/nolibc/stdlib.h
@@ -107,6 +107,7 @@ void free(void *ptr)
  * environment variable exists its value is returned otherwise NULL is
  * returned.
  */
+#ifndef NOLIBC_NO_STARTCODE
 static __attribute__((unused))
 char *getenv(const char *name)
 {
@@ -122,6 +123,7 @@ char *getenv(const char *name)
    }
    return NULL;
 }
+#endif /* NOLIBC_NO_STARTCODE */
static __attribute__((unused))
 void *malloc(size_t len)
diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
index 295e71d34aba..c518a1b4af97 100644
--- a/tools/include/nolibc/sys.h
+++ b/tools/include/nolibc/sys.h
@@ -509,6 +509,7 @@ pid_t gettid(void)
    return sys_gettid();
 }
+#ifndef NOLIBC_NO_STARTCODE
 static unsigned long getauxval(unsigned long key);
/*
@@ -520,7 +521,7 @@ int getpagesize(void)
 {
    return __sysret((int)getauxval(AT_PAGESZ) ?: -ENOENT);
 }
-
+#endif /* NOLIBC_NO_STARTCODE */
/*
  * uid_t getuid(void);
diff --git a/tools/include/nolibc/sys/auxv.h b/tools/include/nolibc/sys/auxv.h
index c52463d6c18d..35d339146463 100644
--- a/tools/include/nolibc/sys/auxv.h
+++ b/tools/include/nolibc/sys/auxv.h
@@ -10,6 +10,8 @@
 #ifndef _NOLIBC_SYS_AUXV_H
 #define _NOLIBC_SYS_AUXV_H
+#ifndef NOLIBC_NO_STARTCODE
+
 #include "../crt.h"
static __attribute__((unused))
@@ -38,4 +40,5 @@ unsigned long getauxval(unsigned long type)
    return ret;
 }
+#endif /* NOLIBC_NO_STARTCODE */
 #endif /* _NOLIBC_SYS_AUXV_H */
-- 
2.51.0



    

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[PATCH 6/9] tools/nolibc: add option to disable startup code