Re: [tcpdump] About HAVE_NO_PRINTF_Z

[Guy Harris via tcpdump-workers <tcpdump-workers () lists tcpdump org>]

> --- Begin Message ---
>
>
> From: Guy Harris <gharris () sonic net>
>
> Date: Thu, 12 Jan 2023 00:10:22 -0800
>
> On Jan 11, 2023, at 11:06 PM, Guy Harris via tcpdump-workers <tcpdump-workers () lists tcpdump org> wrote:
>
> > On UN*Xes, the C library is typically the system API library, so it's bundled with the OS rather than the compiler, 
> > so I don't know whether this is an issue of Sun C 5.9 or SunOS 5.9 (the core OS part of Solaris 9).
>
> Solaris 9 printf() man page:
>
>         https://docs.oracle.com/cd/E19683-01/816-0213/6m6ne387j/index.html
>
> "An optional h specifies that a following d, i, o, u, x, or X conversion character applies to a type short int or type 
> unsigned short int argument (the argument will be promoted according to the integral promotions, and its value 
> converted to type short int or unsigned short int before printing); an optional h specifying that a following n 
> conversion character applies to a pointer to a type short int argument; an optional l (ell) specifying that a following 
> d, i, o, u, x, or X conversion character applies to a type long int or unsigned long int argument; an optional l (ell) 
> specifying that a following n conversion character applies to a pointer to a type long int argument; an optional ll 
> (ell ell) specifying that a following  d, i, o, u, x, or X conversion character applies to a type long long or unsigned 
> long long argument; an optional ll (ell ell) specifying that a following n conversion character applies to a pointer to 
> a long long argument; or an optional L specifying that a following e, E, f, g, or G conversion character applies to a 
> type long double argument. If an h, l, ll, or L appears with any other conversion character, the behavior is undefined."
>
> No mention of z.
>
> Solaris 10 printf() man page:
>
>         https://docs.oracle.com/cd/E19253-01/816-5168/6mbb3hrj1/index.html
>
> "Length Modifiers
>
>         The length modifiers and their meanings are:
>
>                 ...
>
>         z
>
>                 Specifies that a following d, i, o, u, x, or X conversion specifier applies to a size_t or the 
> corresponding signed integer type argument; or that a following n conversion specifier applies to a pointer to a signed 
> integer type corresponding to size_t argument."
>
> So I suspect it's more like "C on Solaris 9 only supports %z if the compiler includes a library with a printf family 
> that supports it and the compiler driver causes programs to be linked with that library before -lc; C on Solaris 10 and 
> later supports %z even if the compiler relies on the system library for printf-family functions".
>
> I don't know whether any C99-supporting versions of GCC, when built on Solaris 9 for Solaris 9, provides their own 
> printf-family functions with %z support.  The GCC 4.6.4 manual says, in section 2 "Language Standards Supported by GCC":
>
>         https://gcc.gnu.org/onlinedocs/gcc-4.6.4/gcc/Standards.html#Standards
>
> in subsection 2.1 "C language":
>
>         The ISO C standard defines (in clause 4) two classes of conforming implementation. A conforming hosted 
> implementation supports the whole standard including all the library facilities; a conforming freestanding 
> implementation is only required to provide certain library facilities: those in <float.h>, <limits.h>, <stdarg.h>, and 
> <stddef.h>; since AMD1, also those in<iso646.h>; and in C99, also those in <stdbool.h> and <stdint.h>. In addition, 
> complex types, added in C99, are not required for freestanding implementations. The standard also defines two 
> environments for programs, a freestanding environment, required of all implementations and which may not have library 
> facilities beyond those required of freestanding implementations, where the handling of program startup and termination 
> are implementation-defined, and a hosted environment, which is not required, in which all the library facilities are 
> provided and startup is through a function int main (void) or int main (int, char *[]). An OS kernel would be a 
> freestanding environment; a program using the facilities of an operating system would normally be in a hosted 
> implementation.
>
>         GCC aims towards being usable as a conforming freestanding implementation, or as the compiler for a conforming 
> hosted implementation. By default, it will act as the compiler for a hosted implementation, defining __STDC_HOSTED__ as 
> 1 and presuming that when the names of ISO C functions are used, they have the semantics defined in the standard. To 
> make it act as a conforming freestanding implementation for a freestanding environment, use the option -ffreestanding; 
> it will then define __STDC_HOSTED__ to 0 and not make assumptions about the meanings of function names from the 
> standard library, with exceptions noted below. To build an OS kernel, you may well still need to make your own 
> arrangements for linking and startup. See Options Controlling C Dialect.
>
>         GCC does not provide the library facilities required only of hosted implementations, nor yet all the facilities 
> required by C99 of freestanding implementations; to use the facilities of a hosted environment, you will need to find 
> them elsewhere (for example, in the GNU C library). See Standard Libraries.
>
> So a conforming freestanding implementation does *not* have to support any of the printf-family routines (something 
> else can provide them, e.g. at least some UN*X kernels provide their own version of sprintf()), and GCC does not 
> provide printf-family routines, as they're required only of hosted implementations.  "Standard Libraries" links to 
> section 11.6 "Standard Libraries":
>
>         https://gcc.gnu.org/onlinedocs/gcc-4.6.4/gcc/Standard-Libraries.html#Standard-Libraries
>
> which says:
>
>         GCC by itself attempts to be a conforming freestanding implementation. See Language Standards Supported by GCC, 
> for details of what this means. Beyond the library facilities required of such an implementation, the rest of the C 
> library is supplied by the vendor of the operating system. If that C library doesn't conform to the C standards, then 
> your programs might get warnings (especially when using -Wall) that you don't expect.
>
>         For example, the sprintf function on SunOS 4.1.3 returns char * while the C standard says that sprintf returns 
> an int. The fixincludes program could make the prototype for this function match the Standard, but that would be wrong, 
> since the function will still return char *.
>
>         If you need a Standard compliant library, then you need to find one, as GCC does not provide one. The GNU C 
> library (called glibc) provides ISO C, POSIX, BSD, SystemV and X/Open compatibility for GNU/Linux and HURD-based GNU 
> systems; no recent version of it supports other systems, though some very old versions did. Version 2.2 of the GNU C 
> library includes nearly complete C99 support. You could also ask your operating system vendor if newer libraries are 
> available.
>
> So merely having GCC 4.6.4 as your compiler doesn't affect whether %z is supported; %z will not work on Solaris 9 and 
> will work on Solaris 10.
>
> So, if we care about %z support:
>
>         on UN*Xes, we'd have to drop support for OSes that don't provide a C library that supports it;
>
>         on Windows with MSVC, we'd have to require a version of MSVC whose library supports it (which I think we do);
>
>         on Windows with other compilers, it depends on whether they provide their own library providing printf-family 
> functions, in which case we'd have to require a compiler version with a library that supports %z, or they use the MSVC 
> library, in which case we'd have to require that a version of the library be the one used.
>
> (The C library was not part of Windows until the Universal C Runtime.  Prior to that, a lot of programs were either 
> statically linked with the C runtime or had an installer that ran Microsoft's installer for the appropriate Visual C 
> runtime.  The Universal C Runtime:
>
>         https://devblogs.microsoft.com/cppblog/introducing-the-universal-crt/
>
> is distributed with Windows; it includes "all of the purely library parts of the CRT", with the remainder, the 
> VCRuntime, which is, I think, still distributed with Visual Studio and which is not, I think, guaranteed to be 
> compiler-independent, "[contains] the compiler support functionality required for things like process startup and 
> exception handling".  I suspect the idea is that you link statically with the VCRuntime, just as you link with crt0.o 
> or whatever the equivalent is called with your compiler/OS on UN*X, and can link dynamically with the Universal C 
> Runtime.)
>
> --- End Message ---
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