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Loading of the vDSO pseudo-hwcap from the type 2 GNU note is a rather arcane and poorly documented process. Given that I had a chance to review this code today I thought I would add all of the things I had to lookup to verify the validity of the process. With a single .note.GNU the vDSO can register up to 64 flags, though in practice you are limited to 64 - _DL_FIRST_EXTRA bits which on x86 is 12 bits. The only use of this that I know of is in the Xen support in Linux where they use the 1st bit to indicate "nosegneg". I see "We use bit 1 to avoid bugs in some versions of glibc when bit 0 is used; the choice is otherwise arbitrary.", but no reference to a glibc bug anywhere. The code as-is should support bit zero, so we still have that free for future use. The kernel, glibc, and ld.so.cache must coordinate to ensure that bit values don't go too high and are used consistently. --- 2013-05-13 Carlos O'Donell <carlos@redhat.com> * elf/dl-hwcaps.c (_dl_important_hwcaps): Comment vDSO hwcap loading. * elf/ldconfig.c (is_hwcap_platform): Comment each hwcap check. (main): Comment "tls" pseudo-hwcap. |
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include | ||
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WUR-REPORT |
This directory contains the sources of the GNU C Library. See the file "version.h" for what release version you have. The GNU C Library is the standard system C library for all GNU systems, and is an important part of what makes up a GNU system. It provides the system API for all programs written in C and C-compatible languages such as C++ and Objective C; the runtime facilities of other programming languages use the C library to access the underlying operating system. In GNU/Linux systems, the C library works with the Linux kernel to implement the operating system behavior seen by user applications. In GNU/Hurd systems, it works with a microkernel and Hurd servers. The GNU C Library implements much of the POSIX.1 functionality in the GNU/Hurd system, using configurations i[4567]86-*-gnu. The current GNU/Hurd support requires out-of-tree patches that will eventually be incorporated into an official GNU C Library release. When working with Linux kernels, this version of the GNU C Library requires Linux kernel version 2.6.16 or later. Also note that the shared version of the libgcc_s library must be installed for the pthread library to work correctly. The GNU C Library supports these configurations for using Linux kernels: i[4567]86-*-linux-gnu x86_64-*-linux-gnu Can build either x86_64 or x32 powerpc-*-linux-gnu Hardware floating point required powerpc64-*-linux-gnu s390-*-linux-gnu s390x-*-linux-gnu sh[34]-*-linux-gnu sparc*-*-linux-gnu sparc64*-*-linux-gnu The code for other CPU configurations supported by volunteers outside of the core glibc maintenance effort is contained in the `ports' add-on, located in the `ports' subdirectory of the source tree. aarch64*-*-linux-gnu alpha*-*-linux-gnu am33*-*-linux-gnu Not currently functional arm-*-linux-gnueabi hppa-*-linux-gnu Not currently functional without patches. ia64-*-linux-gnu m68k-*-linux-gnu mips-*-linux-gnu mips64-*-linux-gnu powerpc-*-linux-gnu Software floating point (--without-fp) tilegx-*-linux-gnu tilepro-*-linux-gnu If you are interested in doing a port, please contact the glibc maintainers; see http://www.gnu.org/software/libc/ for more information. See the file INSTALL to find out how to configure, build, and install the GNU C Library. You might also consider reading the WWW pages for the C library at http://www.gnu.org/software/libc/. The GNU C Library is (almost) completely documented by the Texinfo manual found in the `manual/' subdirectory. The manual is still being updated and contains some known errors and omissions; we regret that we do not have the resources to work on the manual as much as we would like. For corrections to the manual, please file a bug in the `manual' component, following the bug-reporting instructions below. Please be sure to check the manual in the current development sources to see if your problem has already been corrected. Please see http://www.gnu.org/software/libc/bugs.html for bug reporting information. We are now using the Bugzilla system to track all bug reports. This web page gives detailed information on how to report bugs properly. The GNU C Library is free software. See the file COPYING.LIB for copying conditions, and LICENSES for notices about a few contributions that require these additional notices to be distributed. License copyright years may be listed using range notation, e.g., 2000-2013, indicating that every year in the range, inclusive, is a copyrightable year that would otherwise be listed individually.