[PATCH v2 06/11] tools/nolibc: add option to disable runtime

Benjamin Berg
2025-09-19T15:36:08Z

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_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 <benjamin.berg@intel.com>

---
v2:
- Renamed from NOLIBC_NO_STARTCODE to NOLIBC_NO_RUNTIME
- Put the #ifdef around relevant comments
---
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..251c42579028 100644
--- a/tools/include/nolibc/arch-arm.h
+++ b/tools/include/nolibc/arch-arm.h
@@ -184,6 +184,7 @@
_arg1; \
})

+#ifndef NOLIBC_NO_RUNTIME
/* startup code */
void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
{
@@ -193,5 +194,6 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
);
__nolibc_entrypoint_epilogue();
}
+#endif /* NOLIBC_NO_RUNTIME */

#endif /* _NOLIBC_ARCH_ARM_H */
diff --git a/tools/include/nolibc/arch-arm64.h b/tools/include/nolibc/arch-arm64.h
index 02a3f74c8ec8..080a55a7144e 100644
--- a/tools/include/nolibc/arch-arm64.h
+++ b/tools/include/nolibc/arch-arm64.h
@@ -141,6 +141,7 @@
_arg1; \
})

+#ifndef NOLIBC_NO_RUNTIME
/* startup code */
void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
{
@@ -150,4 +151,5 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
);
__nolibc_entrypoint_epilogue();
}
+#endif /* NOLIBC_NO_RUNTIME */
#endif /* _NOLIBC_ARCH_ARM64_H */
diff --git a/tools/include/nolibc/arch-loongarch.h b/tools/include/nolibc/arch-loongarch.h
index 5511705303ea..c894176c3f89 100644
--- a/tools/include/nolibc/arch-loongarch.h
+++ b/tools/include/nolibc/arch-loongarch.h
@@ -142,6 +142,7 @@
_arg1; \
})

+#ifndef NOLIBC_NO_RUNTIME
/* startup code */
void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
{
@@ -151,5 +152,6 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
);
__nolibc_entrypoint_epilogue();
}
+#endif /* NOLIBC_NO_RUNTIME */

#endif /* _NOLIBC_ARCH_LOONGARCH_H */
diff --git a/tools/include/nolibc/arch-m68k.h b/tools/include/nolibc/arch-m68k.h
index 6dac1845f298..2a4fbada5e79 100644
--- a/tools/include/nolibc/arch-m68k.h
+++ b/tools/include/nolibc/arch-m68k.h
@@ -128,6 +128,7 @@
_num; \
})

+#ifndef NOLIBC_NO_RUNTIME
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_RUNTIME */

#endif /* _NOLIBC_ARCH_M68K_H */
diff --git a/tools/include/nolibc/arch-mips.h b/tools/include/nolibc/arch-mips.h
index 0cbac63b249a..a72506ceec6b 100644
--- a/tools/include/nolibc/arch-mips.h
+++ b/tools/include/nolibc/arch-mips.h
@@ -245,6 +245,7 @@

#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)
@@ -266,5 +267,6 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector __
);
__nolibc_entrypoint_epilogue();
}
+#endif /* NOLIBC_NO_RUNTIME */

#endif /* _NOLIBC_ARCH_MIPS_H */
diff --git a/tools/include/nolibc/arch-powerpc.h b/tools/include/nolibc/arch-powerpc.h
index 204564bbcd32..e0c7e0b81f7c 100644
--- a/tools/include/nolibc/arch-powerpc.h
+++ b/tools/include/nolibc/arch-powerpc.h
@@ -183,6 +183,7 @@
#endif
#endif /* !__powerpc64__ */

+#ifndef NOLIBC_NO_RUNTIME
/* startup code */
void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
{
@@ -215,5 +216,6 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
#endif
__nolibc_entrypoint_epilogue();
}
+#endif /* NOLIBC_NO_RUNTIME */

#endif /* _NOLIBC_ARCH_POWERPC_H */
diff --git a/tools/include/nolibc/arch-riscv.h b/tools/include/nolibc/arch-riscv.h
index 885383a86c38..1c00cacf57e1 100644
--- a/tools/include/nolibc/arch-riscv.h
+++ b/tools/include/nolibc/arch-riscv.h
@@ -139,6 +139,7 @@
_arg1; \
})

+#ifndef NOLIBC_NO_RUNTIME
/* startup code */
void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
{
@@ -152,5 +153,6 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
);
__nolibc_entrypoint_epilogue();
}
+#endif /* NOLIBC_NO_RUNTIME */

#endif /* _NOLIBC_ARCH_RISCV_H */
diff --git a/tools/include/nolibc/arch-s390.h b/tools/include/nolibc/arch-s390.h
index df4c3cc713ac..6237211385c0 100644
--- a/tools/include/nolibc/arch-s390.h
+++ b/tools/include/nolibc/arch-s390.h
@@ -139,6 +139,7 @@
_arg1; \
})

+#ifndef NOLIBC_NO_RUNTIME
/* startup code */
void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
{
@@ -155,6 +156,7 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
);
__nolibc_entrypoint_epilogue();
}
+#endif /* NOLIBC_NO_RUNTIME */

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..7a421197d104 100644
--- a/tools/include/nolibc/arch-sh.h
+++ b/tools/include/nolibc/arch-sh.h
@@ -140,6 +140,7 @@
_ret; \
})

+#ifndef NOLIBC_NO_RUNTIME
/* startup code */
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_RUNTIME */

#endif /* _NOLIBC_ARCH_SH_H */
diff --git a/tools/include/nolibc/arch-sparc.h b/tools/include/nolibc/arch-sparc.h
index ca420d843e25..2ebb5686e105 100644
--- a/tools/include/nolibc/arch-sparc.h
+++ b/tools/include/nolibc/arch-sparc.h
@@ -152,6 +152,7 @@
_arg1; \
})

+#ifndef NOLIBC_NO_RUNTIME
/* startup code */
void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
{
@@ -169,6 +170,7 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
);
__nolibc_entrypoint_epilogue();
}
+#endif /* NOLIBC_NO_RUNTIME */

static pid_t getpid(void);

diff --git a/tools/include/nolibc/arch-x86.h b/tools/include/nolibc/arch-x86.h
index d3efc0c3b8ad..11abb8bd7eec 100644
--- a/tools/include/nolibc/arch-x86.h
+++ b/tools/include/nolibc/arch-x86.h
@@ -157,6 +157,7 @@
_eax; \
})

+#ifndef NOLIBC_NO_RUNTIME
/* startup code */
/*
* i386 System V ABI mandates:
@@ -176,6 +177,7 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
);
__nolibc_entrypoint_epilogue();
}
+#endif /* NOLIBC_NO_RUNTIME */

#else /* !defined(__x86_64__) */

@@ -323,6 +325,7 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
_ret; \
})

+#ifndef NOLIBC_NO_RUNTIME
/* startup code */
/*
* x86-64 System V ABI mandates:
@@ -340,6 +343,7 @@ void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _s
);
__nolibc_entrypoint_epilogue();
}
+#endif /* NOLIBC_NO_RUNTIME */

#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..d9262998dae9 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_RUNTIME
+
#include "compiler.h"

char **environ __attribute__((weak));
@@ -88,4 +90,5 @@ void _start_c(long *sp)
exit(exitcode);
}

+#endif /* NOLIBC_NO_RUNTIME */
#endif /* _NOLIBC_CRT_H */
diff --git a/tools/include/nolibc/stackprotector.h b/tools/include/nolibc/stackprotector.h
index c71a2c257177..7123aa056cb0 100644
--- a/tools/include/nolibc/stackprotector.h
+++ b/tools/include/nolibc/stackprotector.h
@@ -9,6 +9,7 @@

#include "compiler.h"

+#ifndef NOLIBC_NO_RUNTIME
#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_RUNTIME */

#endif /* _NOLIBC_STACKPROTECTOR_H */
diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h
index 5fd99a480f82..f184e108ed0a 100644
--- a/tools/include/nolibc/stdlib.h
+++ b/tools/include/nolibc/stdlib.h
@@ -100,6 +100,7 @@ void free(void *ptr)
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
@@ -122,6 +123,7 @@ char *getenv(const char *name)
}
return NULL;
}
+#endif /* NOLIBC_NO_RUNTIME */

static __attribute__((unused))
void *malloc(size_t len)
diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
index 295e71d34aba..a48f5117bfce 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_RUNTIME
static unsigned long getauxval(unsigned long key);

/*
@@ -520,7 +521,7 @@ int getpagesize(void)
{
return __sysret((int)getauxval(AT_PAGESZ) ?: -ENOENT);
}
-
+#endif /* NOLIBC_NO_RUNTIME */

/*
* uid_t getuid(void);
diff --git a/tools/include/nolibc/sys/auxv.h b/tools/include/nolibc/sys/auxv.h
index c52463d6c18d..0e98325e7347 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_RUNTIME
+
#include "../crt.h"

static __attribute__((unused))
@@ -38,4 +40,5 @@ unsigned long getauxval(unsigned long type)
return ret;
}

+#endif /* NOLIBC_NO_RUNTIME */
#endif /* _NOLIBC_SYS_AUXV_H */
--
2.51.0