README
1So you want to add an interface to libc...
2
3CASE I: internal symbols
4
5 A) used in a single file
6 Duh: use whatever name you want and make it static
7
8 B) used in multiple files
9 Give it a name in the implementation namespace (leading underbar)
10 and declare it in a __{BEGIN,END}_HIDDEN_DECLS block in a .h
11 file inside libc. If it's used in just a single subdir of
12 libc *and* that subdir has an appropriate .h file in it, then
13 declare it there.
14 Example: stdio/local.h.
15 Otherwise, declare it in one of the hidden/* files.
16 Example: _mktemp() in hidden/stdio.h
17
18CASE II: external symbols
19
20 First of all, add your symbol to Symbols.list. MD symbols go in
21 arch/*/Symbols.list (shock, I know)
22
23 Declare your function in the appropriate header. It almost certainly
24 should be in a public header installed under /usr/include/. Exceptions
25 are symbols that are just shared between libc and libpthread/csu/ld.so
26 which are only declared in libc/include/* or just in each .c file.
27
28 A) objects (variables)
29 That's it, you're done.
30
31
32 B) plain C functions (not syscalls)
33 1) functions that are *not* called from inside libc
34
35 If this function is specified in the ISO C standard or its
36 name begins with an underbar, then in the hidden/* version
37 of the header where you declared the function, add this line:
38 PROTO_STD_DEPRECATED(your_function_name);
39
40 Otherwise, this is *not* a function specified in the ISO C
41 standard and its name begins with a letter. In the hidden/*
42 version of the header where you declared the function, add
43 this line:
44 PROTO_DEPRECATED(your_function_name);
45
46 Note: the "DEPRECATED" suffix is about a detail of
47 how the macros work and has nothing to do with whether the
48 function itself is a Good Thing vs deprecated.
49
50 2) functions that are called from inside libc
51
52 In the hidden/* version of the header where you declared
53 the function, add this line:
54 PROTO_NORMAL(your_function_name);
55
56 Then, in the .c file(s) where the function is defined:
57 - if the function is specified in the ISO C standard or
58 its name begins with an underbar, add
59 DEF_STRONG(your_function_name);
60
61 - otherwise, add:
62 DEF_WEAK(your_function_name);
63
64
65 C) syscalls that don't require any wrapping
66
67 In the hidden/* version of the header where you declared the
68 function, add this line:
69 PROTO_NORMAL(your_function_name);
70
71 Generate the stub by adding it to the ASM variable in
72 libc/sys/Makefile.inc
73
74
75 D) syscalls that require cancellation or similar wrappers that don't
76 change the function signature
77
78 Generate the stub by adding it to the HIDDEN (*not* ASM!)
79 variable in libc/sys/Makefile.inc
80
81 In the hidden/* version of the header where you declared the
82 function, add this line:
83 PROTO_WRAP(your_function_name);
84
85 The wrapper function should be defined in
86 libc/sys/w_your_function_name.c
87 which should define WRAP(your_function_name) and follow it
88 with DEF_WRAP(your_function_name). Look at libc/sys/w_sigaction.c
89 for an example.
90
91 By default, libc code that calls your_function_name() will get
92 the real syscall and *not* the wrapper. libc calls that need
93 to go through the wrapper should invoke WRAP(your_function_name)
94
95
96 E) syscalls that require libc wrappers for other reasons
97 First of all, make sure this really is the Right Thing. Talk
98 with kettenis, deraadt, millert, and guenther.
99
100 If the actual syscall doesn't have the same calling convention
101 as the C interface, then maybe it shouldn't be exported at all
102 and you should just have an ASM stub, like SYS___tfork -->
103 __tfork_thread() or SYS_break --> brk() and sbrk(). If it
104 _could_ be called from C, then give the syscall a name different
105 from the C API. Syscalls that fail this for historical reasons
106 (e.g., exit == _exit(2)) are generated with PSEUDO/PSEUDO_NOERR
107 in libc/sys/Makefile.inc, so the ASM stub has a leading underbar.
108 Go read gen/getlogin.c rev 1.13 for an example of how to do
109 this, but don't pick this option, really.
110
111