Re: gnulib fails for build on Mac OS X 10.4: get_ppid_of.c:36:22: error: libproc.h: No such file or directory

[Evan Miller]

I'm sorry I missed out on this discussion but the patch below is problematic.

proc_pidinfo is a system function not available on 10.4. When compiling with 
the 10.5 SDK and deploying to 10.4, a run-time link error will result on 10.4 
using the patch.

Generally, it is preferable to use MAX_ALLOWED when using compile-time 
constants (say integers) that may be gracefully handled as a run-time error on 
the unsupported system, and to use MIN_REQUIRED when invoking functions not 
present on the older systems.

It may seem like a problem that the newer system will not use the new SDK 
function, but the alternative is for the old system to have a broken binary. 
The ideal of course is run-time function detection with weak linking; Apple 
introduced this later in Objective-C and Swift with the @available macro, but 
AFAIK it's not an option in this context.

Thanks for your attention to this.

Evan

> On Dec 11, 2021, at 11:55, Bruno Haible <bruno@clisp.org> wrote:
> 
> Hi Ryan,
> 
> Thank you for the extensive explanations. The MAC_OS_X_VERSION_MAX_ALLOWED /
> MAC_OS_X_VERSION_MIN_REQUIRED pair makes perfect sense.
> 
>> In 10.5, Apple introduced a new header Availability.h which they want you to
>> use instead of AvailabilityMacros.h
> 
> Huh? The comments in Availability.h say "These macros are for use in OS header
> files." So, as I understand it, Availability.h is to be used in OS header 
> files
> and AvailabilityMacros.h in application code.
> 
>> A MacPorts user running Mac OS X 10.4 proposed this fix which just hides the 
>> #include of <libproc.h> and its uses behind the 10.5 deployment target 
>> check, without attempting to provide any alternative when deploying for 
>> earlier versions nor attempting to allow libproc features to be used if 
>> running on 10.5 or greater when compiled for 10.4. I commented that I did 
>> not know whether this fix was correct and asked them to bring it up on this 
>> list, but since I don't think they have, I'm bringing it up for them.
>> 
>> https://github.com/macports/macports-ports/pull/13226/files#diff-8a2ad00cea356fb07a25e323fde8a18232252de4f6421d5e73347aa845d56045
> 
> That's the major problem of this patch, indeed: "nor attempting to allow
> libproc features to be used if running on 10.5 or greater when compiled
> for 10.4".
> 
> I'm committing the patch below, which implements optimal behaviour for
> any pair of MAC_OS_X_VERSION_MAX_ALLOWED / MAC_OS_X_VERSION_MIN_REQUIRED.
> 
>> (They used __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ instead of 
>> MAC_OS_X_VERSION_MIN_REQUIRED; the distinction is not clear to me. It might 
>> be that __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ is defined even if 
>> AvailabilityMacros.h is not included.)
> 
> I'll prefer to use the macros without __ prefix; it looks safer to use
> AvailabilityMacros.h than to bypass it.
> 
>> We may also need to think about what happens when compiling for a non-macOS 
>> Apple OS (iOS, iPadOS, tvOS, watchOS). I don't think *MAC_OS_X* defines will 
>> be defined on those other OSes. In MacPorts we don't try to solve the 
>> problem since we only compile for macOS.
> 
> In Gnulib as well, no one has attempted ports to iOS and its derivatives.
> 
> 
> 2021-12-11  Bruno Haible  <bruno@clisp.org>
> 
>       get_ppid_of, get_progname_of: Fix compilation error on Mac OS X < 10.5.
>       Reported by Ryan Schmidt <gnulib@ryandesign.com> in
>       <https://lists.gnu.org/archive/html/bug-gnulib/2021-12/msg00011.html>.
>       * lib/get_ppid_of.c: Include AvailabilityMacros.h
>       (get_ppid_of): Use MAC_OS_X_VERSION_MAX_ALLOWED and
>       MAC_OS_X_VERSION_MIN_REQUIRED.
>       * lib/get_progname_of: Include AvailabilityMacros.h
>       (get_progname_of): Use MAC_OS_X_VERSION_MAX_ALLOWED and
>       MAC_OS_X_VERSION_MIN_REQUIRED.
> 
> diff --git a/lib/get_ppid_of.c b/lib/get_ppid_of.c
> index f153b7539..dd4e38129 100644
> --- a/lib/get_ppid_of.c
> +++ b/lib/get_ppid_of.c
> @@ -33,7 +33,13 @@
> #endif
> 
> #if defined __APPLE__ && defined __MACH__                   /* Mac OS X */
> -# include <libproc.h>
> +/* Get MAC_OS_X_VERSION_MIN_REQUIRED, MAC_OS_X_VERSION_MAX_ALLOWED.
> +   The version at runtime satisfies
> +   MAC_OS_X_VERSION_MIN_REQUIRED <= version <= MAC_OS_X_VERSION_MAX_ALLOWED. 
>  */
> +# include <AvailabilityMacros.h>
> +# if MAC_OS_X_VERSION_MAX_ALLOWED >= 1050
> +#  include <libproc.h>
> +# endif
> #endif
> 
> #if defined _AIX                                            /* AIX */
> @@ -226,14 +232,19 @@ get_ppid_of (pid_t pid)
> #endif
> 
> #if defined __APPLE__ && defined __MACH__                   /* Mac OS X */
> +# if MAC_OS_X_VERSION_MAX_ALLOWED >= 1050
> 
> -# if defined PROC_PIDT_SHORTBSDINFO
> +  /* Mac OS X >= 10.7 has PROC_PIDT_SHORTBSDINFO.  */
> +#  if defined PROC_PIDT_SHORTBSDINFO
>   struct proc_bsdshortinfo info;
> 
>   if (proc_pidinfo (pid, PROC_PIDT_SHORTBSDINFO, 0, &info, sizeof (info))
>       == sizeof (info))
>     return info.pbsi_ppid;
> -# else
> +#  endif
> +
> +#  if MAC_OS_X_VERSION_MIN_REQUIRED < 1070
> +  /* For older versions, use PROC_PIDTBSDINFO instead.  */
>   /* Note: The second part of 'struct proc_bsdinfo' differs in size between
>      32-bit and 64-bit environments, and the kernel of Mac OS X 10.5 knows
>      only about the 32-bit 'struct proc_bsdinfo'.  Fortunately all the info
> @@ -242,8 +253,9 @@ get_ppid_of (pid_t pid)
> 
>   if (proc_pidinfo (pid, PROC_PIDTBSDINFO, 0, &info, 128) == 128)
>     return info.pbi_ppid;
> -# endif
> +#  endif
> 
> +# endif
> #endif
> 
> #if defined _AIX                                            /* AIX */
> diff --git a/lib/get_progname_of.c b/lib/get_progname_of.c
> index 46144e742..bdda3c60d 100644
> --- a/lib/get_progname_of.c
> +++ b/lib/get_progname_of.c
> @@ -41,7 +41,13 @@
> #endif
> 
> #if defined __APPLE__ && defined __MACH__                   /* Mac OS X */
> -# include <libproc.h>
> +/* Get MAC_OS_X_VERSION_MIN_REQUIRED, MAC_OS_X_VERSION_MAX_ALLOWED.
> +   The version at runtime satisfies
> +   MAC_OS_X_VERSION_MIN_REQUIRED <= version <= MAC_OS_X_VERSION_MAX_ALLOWED. 
>  */
> +# include <AvailabilityMacros.h>
> +# if MAC_OS_X_VERSION_MAX_ALLOWED >= 1050
> +#  include <libproc.h>
> +# endif
> #endif
> 
> #if defined _AIX                                            /* AIX */
> @@ -266,14 +272,19 @@ get_progname_of (pid_t pid)
> #endif
> 
> #if defined __APPLE__ && defined __MACH__                   /* Mac OS X */
> +# if MAC_OS_X_VERSION_MAX_ALLOWED >= 1050
> 
> -# if defined PROC_PIDT_SHORTBSDINFO
> +  /* Mac OS X >= 10.7 has PROC_PIDT_SHORTBSDINFO.  */
> +#  if defined PROC_PIDT_SHORTBSDINFO
>   struct proc_bsdshortinfo info;
> 
>   if (proc_pidinfo (pid, PROC_PIDT_SHORTBSDINFO, 0, &info, sizeof (info))
>       == sizeof (info))
>     return strdup (info.pbsi_comm);
> -# else
> +#  endif
> +
> +#  if MAC_OS_X_VERSION_MIN_REQUIRED < 1070
> +  /* For older versions, use PROC_PIDTBSDINFO instead.  */
>   /* Note: The second part of 'struct proc_bsdinfo' differs in size between
>      32-bit and 64-bit environments, and the kernel of Mac OS X 10.5 knows
>      only about the 32-bit 'struct proc_bsdinfo'.  Fortunately all the info
> @@ -282,8 +293,9 @@ get_progname_of (pid_t pid)
> 
>   if (proc_pidinfo (pid, PROC_PIDTBSDINFO, 0, &info, 128) == 128)
>     return strdup (info.pbi_comm);
> -# endif
> +#  endif
> 
> +# endif
> #endif
> 
> #if defined _AIX                                            /* AIX */
> 
> 
> 
> 
>