Sometimes I wonder whether the C library maintainers want to actually#

Sun, 24 Aug 2003 22:09:08 +0000

Sometimes I wonder whether the C library maintainers want to actually discourage programmers from e.g. writing signal handlers. In glibc 2.3.1 on the 32 bit PowerPC, it was possible to access machine registers in a signal context (e.g. from a SA_SIGINFO signal handler) by doing something like

   ((context->uc_mcontext.regs)->gpr[offset])

In 2.3.2 this fails with the message

  error: structure has no member named `regs'

It looks from a brief inspection of the glibc cvs as though changes to the ucontext structure were made for compatibility purposes with ppc64. Which is probably reasonable; can't stand in the way of progress, Mr Dent. So this code should now be

   ((context->uc_mcontext.gregs)[offset]);

The problem, of course, is that this code doesn't build on the older version, which a lot of people (me, certainly, and most other people probably) are still using. So, this calls for conditional compilation based on some header feature: icky, maybe, but necessary.

1. define GLIBC 2
2. define GLIBCMINOR_ 3
   <features.h>

Whoever wrote this file obviously subscribed to the (quite sensible, IMO) point of view that new features were not going to be introduced in patchlevel releases. Whoever added the 64 bit support, which breaks our source code compatibility, seems to have quite different ideas :-(