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.
Signed-off-by: Zhangjin Wu <falcon@xxxxxxxxxxx>
---
tools/include/nolibc/crt.h | 44 ++++++++++++++++++++++++++++++++++++++
1 file changed, 44 insertions(+)
diff --git a/tools/include/nolibc/crt.h b/tools/include/nolibc/crt.h
index 221b7c5346ca..b269294e9664 100644
--- a/tools/include/nolibc/crt.h
+++ b/tools/include/nolibc/crt.h
@@ -13,4 +13,48 @@
char **environ __attribute__((weak));
const unsigned long *_auxv __attribute__((weak));
+int main(int argc, char *argv[], char **envp);
+static void exit(int);
+
+void _start_c(long *sp)
+{
+ int argc, i;
+ char **argv;
+ char **envp;
+
+ /*
+ * 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(main(argc, argv, envp));
+}
+
#endif /* _NOLIBC_CRT_H */
--
2.25.1
