As the environ and _auxv support added for nolibc, the assembly _start function becomes more and more complex and therefore makes the porting of nolibc to new architectures harder and harder. To simplify portability, this C version of _start_c() is added to do most of the assembly start operations in C, which reduces the complexity a lot and will eventually simplify the porting of nolibc to the new architectures. The new _start_c() only requires a stack pointer argument, it will find argv, envp and _auxv for us, and then call main(), finally, it exit() with main's return status. With this new _start_c(), the future new architectures only require to add very few assembly instructions. As suggested by Thomas, users may use a different signature of main (e.g. void main(void)), a _nolibc_main alias is added for main to silence the warning about potential conflicting types. Suggested-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx> Link: https://lore.kernel.org/lkml/90fdd255-32f4-4caf-90ff-06456b53dac3@xxxxxxxx/ Signed-off-by: Zhangjin Wu <falcon@xxxxxxxxxxx> --- tools/include/nolibc/Makefile | 1 + tools/include/nolibc/crt.h | 59 +++++++++++++++++++++++++++++++++++ 2 files changed, 60 insertions(+) create mode 100644 tools/include/nolibc/crt.h diff --git a/tools/include/nolibc/Makefile b/tools/include/nolibc/Makefile index 64d67b080744..909b6eb500fe 100644 --- a/tools/include/nolibc/Makefile +++ b/tools/include/nolibc/Makefile @@ -27,6 +27,7 @@ nolibc_arch := $(patsubst arm64,aarch64,$(ARCH)) arch_file := arch-$(nolibc_arch).h all_files := \ compiler.h \ + crt.h \ ctype.h \ errno.h \ nolibc.h \ diff --git a/tools/include/nolibc/crt.h b/tools/include/nolibc/crt.h new file mode 100644 index 000000000000..f9db2389acd2 --- /dev/null +++ b/tools/include/nolibc/crt.h @@ -0,0 +1,59 @@ +/* SPDX-License-Identifier: LGPL-2.1 OR MIT */ +/* + * C Run Time support for NOLIBC + * Copyright (C) 2023 Zhangjin Wu <falcon@xxxxxxxxxxx> + */ + +#ifndef _NOLIBC_CRT_H +#define _NOLIBC_CRT_H + +char **environ __attribute__((weak)); +const unsigned long *_auxv __attribute__((weak)); + +typedef int (_nolibc_main_fn)(int, char **, char **); +static void exit(int); + +void _start_c(long *sp) +{ + int argc, i; + char **argv; + char **envp; + /* silence potential warning: conflicting types for 'main' */ + _nolibc_main_fn _nolibc_main __asm__ ("main"); + + /* + * sp : argc <-- argument count, required by main() + * argv: argv[0] <-- argument vector, required by main() + * argv[1] + * ... + * argv[argc-1] + * null + * envp: envp[0] <-- environment variables, required by main() and getenv() + * envp[1] + * ... + * null + * _auxv: auxv[0] <-- auxiliary vector, required by getauxval() + * auxv[1] + * ... + * null + */ + + /* assign argc and argv */ + argc = sp[0]; + argv = (void *)(sp + 1); + + /* find envp */ + envp = argv + argc + 1; + environ = envp; + + /* find auxv */ + i = 0; + while (envp[i]) + i++; + _auxv = (void *)(envp + i + 1); + + /* go to application */ + exit(_nolibc_main(argc, argv, envp)); +} + +#endif /* _NOLIBC_CRT_H */ -- 2.25.1
