On Mon, 17 Jun 2013, Jan Beulich wrote: > expect runtime properties to be taken into account here. And > for cross builds I'd expect a way to control whether the final > binary would be using GNU IFUNC symbols rather than just > making this dependent upon tool chain capabilities.
For cross builds to glibc target I'd quite like a --with-glibc-version or similar configure option that specifies the (minimum) version of glibc assumed to be present on the target (strictly, for glibc multilibs, in the case of a toolchain mixing glibc and non-glibc multilibs, though not all relevant features effectively support per-multilib configuration). At present, there is some code in gcc/configure.ac that checks the target's features.h if this is available at configure time, some checking bits/wordsize.h for a different purpose, and some that checks for native configuration and runs ldd --version (for STB_GNU_UNIQUE support), which isn't cross-friendly at all. This should be refactored to a single place where a target glibc version (major and minor version numbers) is determined, which could then use a new configure option specifying the target version to assume if headers should not be used to detect it. Such a configure macro could I suppose be made usable in target library configuration, though the cases I've been interested in are cases of configuring the compiler itself. Making a configure option override version detection from target headers (version detection from ldd --version should simply be avoided completely and replaced by use of headers / configure option) is useful, in particular, when building an initial bootstrap compiler before target glibc headers are available. Specifically, if you want such a compiler to build a glibc the same as would be the eventual result of an iterative process of alternating GCC and glibc builds, without needing to override any autoconf tests in either GCC or glibc with *_cv_* settings, such an option is needed as I described in <http://sourceware.org/ml/libc-alpha/2012-09/msg00093.html> to avoid needing to pass gcc_cv_libc_provides_ssp=yes on some architectures when configuring the initial bootstrap GCC. -- Joseph S. Myers jos...@codesourcery.com
