xref: /openbmc/linux/include/uapi/linux/libc-compat.h (revision 827634ad)
1 /*
2  * Compatibility interface for userspace libc header coordination:
3  *
4  * Define compatibility macros that are used to control the inclusion or
5  * exclusion of UAPI structures and definitions in coordination with another
6  * userspace C library.
7  *
8  * This header is intended to solve the problem of UAPI definitions that
9  * conflict with userspace definitions. If a UAPI header has such conflicting
10  * definitions then the solution is as follows:
11  *
12  * * Synchronize the UAPI header and the libc headers so either one can be
13  *   used and such that the ABI is preserved. If this is not possible then
14  *   no simple compatibility interface exists (you need to write translating
15  *   wrappers and rename things) and you can't use this interface.
16  *
17  * Then follow this process:
18  *
19  * (a) Include libc-compat.h in the UAPI header.
20  *      e.g. #include <linux/libc-compat.h>
21  *     This include must be as early as possible.
22  *
23  * (b) In libc-compat.h add enough code to detect that the comflicting
24  *     userspace libc header has been included first.
25  *
26  * (c) If the userspace libc header has been included first define a set of
27  *     guard macros of the form __UAPI_DEF_FOO and set their values to 1, else
28  *     set their values to 0.
29  *
30  * (d) Back in the UAPI header with the conflicting definitions, guard the
31  *     definitions with:
32  *     #if __UAPI_DEF_FOO
33  *       ...
34  *     #endif
35  *
36  * This fixes the situation where the linux headers are included *after* the
37  * libc headers. To fix the problem with the inclusion in the other order the
38  * userspace libc headers must be fixed like this:
39  *
40  * * For all definitions that conflict with kernel definitions wrap those
41  *   defines in the following:
42  *   #if !__UAPI_DEF_FOO
43  *     ...
44  *   #endif
45  *
46  * This prevents the redefinition of a construct already defined by the kernel.
47  */
48 #ifndef _UAPI_LIBC_COMPAT_H
49 #define _UAPI_LIBC_COMPAT_H
50 
51 /* We have included glibc headers... */
52 #if defined(__GLIBC__)
53 
54 /* Coordinate with glibc netinet/in.h header. */
55 #if defined(_NETINET_IN_H)
56 
57 /* GLIBC headers included first so don't define anything
58  * that would already be defined. */
59 #define __UAPI_DEF_IN6_ADDR		0
60 /* The exception is the in6_addr macros which must be defined
61  * if the glibc code didn't define them. This guard matches
62  * the guard in glibc/inet/netinet/in.h which defines the
63  * additional in6_addr macros e.g. s6_addr16, and s6_addr32. */
64 #if defined(__USE_MISC) || defined (__USE_GNU)
65 #define __UAPI_DEF_IN6_ADDR_ALT		0
66 #else
67 #define __UAPI_DEF_IN6_ADDR_ALT		1
68 #endif
69 #define __UAPI_DEF_SOCKADDR_IN6		0
70 #define __UAPI_DEF_IPV6_MREQ		0
71 #define __UAPI_DEF_IPPROTO_V6		0
72 #define __UAPI_DEF_IPV6_OPTIONS		0
73 #define __UAPI_DEF_IN6_PKTINFO		0
74 #define __UAPI_DEF_IP6_MTUINFO		0
75 
76 #else
77 
78 /* Linux headers included first, and we must define everything
79  * we need. The expectation is that glibc will check the
80  * __UAPI_DEF_* defines and adjust appropriately. */
81 #define __UAPI_DEF_IN6_ADDR		1
82 /* We unconditionally define the in6_addr macros and glibc must
83  * coordinate. */
84 #define __UAPI_DEF_IN6_ADDR_ALT		1
85 #define __UAPI_DEF_SOCKADDR_IN6		1
86 #define __UAPI_DEF_IPV6_MREQ		1
87 #define __UAPI_DEF_IPPROTO_V6		1
88 #define __UAPI_DEF_IPV6_OPTIONS		1
89 #define __UAPI_DEF_IN6_PKTINFO		1
90 #define __UAPI_DEF_IP6_MTUINFO		1
91 
92 #endif /* _NETINET_IN_H */
93 
94 /* Definitions for xattr.h */
95 #if defined(_SYS_XATTR_H)
96 #define __UAPI_DEF_XATTR		0
97 #else
98 #define __UAPI_DEF_XATTR		1
99 #endif
100 
101 /* If we did not see any headers from any supported C libraries,
102  * or we are being included in the kernel, then define everything
103  * that we need. */
104 #else /* !defined(__GLIBC__) */
105 
106 /* Definitions for in6.h */
107 #define __UAPI_DEF_IN6_ADDR		1
108 #define __UAPI_DEF_IN6_ADDR_ALT		1
109 #define __UAPI_DEF_SOCKADDR_IN6		1
110 #define __UAPI_DEF_IPV6_MREQ		1
111 #define __UAPI_DEF_IPPROTO_V6		1
112 #define __UAPI_DEF_IPV6_OPTIONS		1
113 #define __UAPI_DEF_IN6_PKTINFO		1
114 #define __UAPI_DEF_IP6_MTUINFO		1
115 
116 /* Definitions for xattr.h */
117 #define __UAPI_DEF_XATTR		1
118 
119 #endif /* __GLIBC__ */
120 
121 #endif /* _UAPI_LIBC_COMPAT_H */
122