@@ -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 \
new file mode 100644
@@ -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 **);
+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 */
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