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Gotchas When Building Software in PASE

Gotchas When Building Software in PASE

malloc behaves differently from many other platforms

Zero byte allocations on AIX can be strange. If software depends on this behaviour, you can build with -D_LINUX_SOURCE_COMPAT to enable a built-into-libc wrapper that has the glibc behaviour.

C++ issues

Make sure that you have libstdcplusplus-devel in addition to g++ installed.

If you run into issues with the threading parts of the C++ standard library, such as std::mutex, ensure that -pthread is passed to g++. This will flip some defines and such so that threading is exposed. Linking pthread (-pthread if you use GCC as the linker, otherwise -lpthread) in also helps with crashes in C++ standard library locale code.

AF_LOCAL not declared

error: 'AF_LOCAL' was not declared in this scope
     c = socket(AF_LOCAL, SOCK_STREAM, 0);
                ^~~~~~~~

On some platforms, AF_LOCAL is provided as a synonym of AF_UNIX, but not on AIX/PASE. Either alter the code to use AF_UNIX directly or add your own synonym:

#ifndef AF_LOCAL
#define AF_LOCAL AF_UNIX
#endif

// ...
c = socket(AF_LOCAL, SOCK_STREAM, 0);

TOC overflow

ld: 0711-781 ERROR: TOC overflow. TOC size: 85080       Maximum size: 65536
collect2: error: ld returned 12 exit status

Understanding the TOC (table of contents) could take up its own entire article. Indeed there’s a good one here. The usual way to fix is by passing -bbigtoc option to the linker (ld). Using GCC, you need to prefix linker flags with -Wl, and these flags are specified in $LDFLAGS:

export LDFLAGS='-Wl,-bbigtoc'
./configure ...
make ...

While -bbigtoc should always do the job, it’s not the most efficient. GCC also has additional ways to reduce TOC pressure that may be better performing, but you’ll need to understand the code you’re trying to compile and what each option does to apply them. Look for more info on the following compiler options here:

  • -mno-fp-in-toc
  • -mno-sum-in-toc
  • -mminimal-toc
  • -mcmodel=medium
  • -mcmodel=large

readdir_r return values

On AIX and PASE, readdir_r returns 9 and sets the result to NULL for both end of directory and error; on error, it sets errno. This is unlike other Unix systens and very easy to use incorrectly even when adapting to its quirks, so you can try:

  • Set errno to 0 before calling. This means you can disambiguate between the cases.
  • Build with -D_LINUX_SOURCE_COMPAT. This will point readdir_r to an alternative version with glibc-like semantics.

uname return values

Mostly a cosmetic issue, but applications expecting a full version in the release field of utsname will be disappointed. AIX and PASE put the major version (you know, the “V” in “V7R3”) in version, and the minor version (the “R”) in release.

Thread safety

AIX and PASE are not thread safe by default. You should pass -D_THREAD_SAFE, which enables important things like a thread-safe errno.

VFS woes

mntctl, statvfs, and ILE statvfs can never agree on a consistent value for magic names and numbers, unlike AIX. Try to avoid converting between their values.

SIOCGIFCONF

On PASE, SIOCGIFCONF doesn’t show the true line description name, nor does it return an AF_LINK entry; the device will have a fake name based on its IPv4 address. This makes getting the interface index and MAC address nearly impossible; you can’t even use if_nameindex because that returns the true line description name. As an alternative, you can use Qp2getifaddrs, which works like most Unix-like systems’ getifaddrs.