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2.4.3 Unsupported Platforms

Some platforms with C compilers are not supported by Gnulib because the platforms violate Gnulib’s C portability assumptions. See Other portability assumptions made by Gnulib.

These assumptions are not required by the C or POSIX standards but hold on almost all practical porting targets. If you need to port Gnulib code to a platform where these assumptions are not true, we would appreciate hearing of any fixes. We need fixes that do not increase runtime overhead on standard hosts and that are relatively easy to maintain.

These platforms are listed below to illustrate problems that Gnulib and Gnulib-using code would have if it were intended to be portable to all practical POSIX or C platforms.

• Clang’s -fsanitize=undefined option causes the program to crash if it adds zero to a null pointer – behavior that is undefined in strict C, but which yields a null pointer on all practical porting targets and which the Gnulib portability guidelines allow.

  If you use Clang with -fsanitize=undefined, you can work around the problem by also using ‘-fno-sanitize=pointer-overflow’, although this may also disable some unrelated and useful pointer checks. Perhaps someday the Clang developers will fix the infelicity.

• The IBM i’s pointers are 128 bits wide and it lacks the two types intptr_t and uintptr_t, which are optional in the C and POSIX standards. However, these two types are required for the XSI extension to POSIX, and many Gnulib modules use them. To work around this compatibility problem, Gnulib-using applications can be run on the IBM i’s PASE emulation environment. The IBM i’s architecture descends from the System/38 (1978).
• The Unisys ClearPath Dorado’s machine word is 36 bits. Its signed integers use a ones’-complement representation. On these machines, CHAR_BIT == 9 and INT_MIN == -INT_MAX. By default UINT_MAX is 2^{36} - 2, which does not conform to the C requirement that it be one less than a power of two. Although compiler options can raise UINT_MAX to be 2^{36} - 1, this can break system code that uses -0 as a flag value. This platform’s architecture descends from the UNIVAC 1103 (1953).
• The Unisys ClearPath Libra’s machine word is 48 bits with a 4-bit tag and a 4-bit data extension. Its unsigned int uses the low-order 40 bits of the word, and int uses the low-order 41 bits of the word with a signed-magnitude representation. On these machines, INT_MAX == UINT_MAX, INT_MIN == -INT_MAX, and sizeof (int) == 6. This platform’s architecture descends from the Burroughs B5000 (1961).

The following platforms are not supported by Gnulib. The cost of supporting them would exceed the benefit because they are rarely used, or poorly documented, or have been supplanted by other platforms, or diverge too much from POSIX, or some combination of these and other factors. Please don’t bother sending us patches for them.

• Windows 95/98/ME.
• DJGPP and EMX (the 32-bit operating systems running in DOS).
• MSDOS (the 16-bit operating system).
• Windows Mobile, Symbian OS, iOS.