Hi, Thomas
On 2023-07-12 17:17:39+0800, Zhangjin Wu wrote:
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@weissschuh.net Link: https://lore.kernel.org/lkml/90fdd255-32f4-4caf-90ff-06456b53dac3@t-8ch.de/ Signed-off-by: Zhangjin Wu falcon@tinylab.org
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 \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@tinylab.org
- */
+#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 **);
What's the advantage of the typedef over using the pointer type inline?
With the extra comment added, this is not required anymore, will remove this typedef.
+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");
What about the stackprotector initialization? It would really fit great into this series.
Ok, which gcc version supports stackprotector? seems the test even skip on gcc 10, I will find one to verify the code change.
- /*
* 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);
Bit of a weird mismatch between array syntax and pointer arithmetic.
This 'argc = *sp;' may be better ;-)
- /* find envp */
- envp = argv + argc + 1;
- environ = envp;
Is envp really needed? Could just be assigned directly to environ.
Ok, let's save one variable, envp is used to be consistent with the frequenty declaration of main().
- /* find auxv */
- i = 0;
- while (envp[i])
i++;- _auxv = (void *)(envp + i + 1);
Could be simplified a bit:
_auxv = (void *) envp; while (_auxv) _auxv++;
Yeah, it is better, but needs a little change.
_auxv = (void *) envp; while (*_auxv) _auxv++; _auxv++;
Thanks, Zhangjin
- /* go to application */
- exit(_nolibc_main(argc, argv, envp));
+}
+#endif /* _NOLIBC_CRT_H */
2.25.1