xref: /freebsd/stand/kboot/libkboot/crt1.c (revision a90b9d0159070121c221b966469c3e36d912bf82)
1 /*
2  * Copyright (c) 2022, Netflix, Inc.
3  *
4  * SPDX-License-Identifier: BSD-2-Clause
5  */
6 
7 /*
8  * MI part of the C startup code. We take a long * pointer (we assume long is
9  * the same size as a pointer, as the Linux world is wont to do). We get a
10  * pointer to the stack with the main args on it. We don't bother decoding the
11  * aux vector, but may need to do so in the future.
12  *
13  * The long *p points to:
14  *
15  * +--------------------+
16  * | argc               | Small address
17  * +--------------------+
18  * | argv[0]            | argv
19  * +--------------------+
20  * | argv[1]            |
21  * +--------------------+
22  *  ...
23  * +--------------------+
24  * | NULL               | &argv[argc]
25  * +--------------------+
26  * | envp[0]            | envp
27  * +--------------------+
28  * | envp[1]            |
29  * +--------------------+
30  *  ...
31  * +--------------------+
32  * | NULL               |
33  * +--------------------+
34  * | aux type           | AT_xxxx
35  * +--------------------+
36  * | aux value          |
37  * +--------------------+
38  * | aux type           | AT_xxxx
39  * +--------------------+
40  * | aux value          |
41  * +--------------------+
42  * | aux type           | AT_xxxx
43  * +--------------------+
44  * | aux value          |
45  * +--------------------+
46  *...
47  * +--------------------+
48  * | NULL               |
49  * +--------------------+
50  *
51  * The AUX vector contains additional information for the process to know from
52  * the kernel (not parsed currently). AT_xxxx constants are small (< 50).
53  */
54 
55 extern void _start_c(long *);
56 extern int main(int, const char **, char **);
57 
58 #include "start_arch.h"
59 
60 void
61 _start_c(long *p)
62 {
63 	int argc;
64 	const char **argv;
65 	char **envp;
66 
67 	argc = p[0];
68 	argv = (const char **)(p + 1);
69 	envp = (char **)argv + argc + 1;
70 
71 	/* Note: we don't ensure that fd 0, 1, and 2 are sane at this level */
72 	/* Also note: we expect main to exit, not return off the end */
73 	main(argc, argv, envp);
74 }
75