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Linux 6.13 (662df3e5c3766) added a lightweight way to define guard areas through madvise syscall. Instead of PROT_NONE the guard region through mprotect, userland can madvise the same area with a special flag, and the kernel ensures that accessing the area will trigger a SIGSEGV (as for PROT_NONE mapping). The madvise way has the advantage of less kernel memory consumption for the process page-table (one less VMA per guard area), and slightly less contention on kernel (also due to the fewer VMA areas being tracked). The pthread_create allocates a new thread stack in two ways: if a guard area is set (the default) it allocates the memory range required using PROT_NONE and then mprotect the usable stack area. Otherwise, if a guard page is not set it allocates the region with the required flags. For the MADV_GUARD_INSTALL support, the stack area region is allocated with required flags and then the guard region is installed. If the kernel does not support it, the usual way is used instead (and MADV_GUARD_INSTALL is disabled for future stack creations). The stack allocation strategy is recorded on the pthread struct, and it is used in case the guard region needs to be resized. To avoid needing an extra field, the 'user_stack' is repurposed and renamed to 'stack_mode'. This patch also adds a proper test for the pthread guard. I checked on x86_64, aarch64, powerpc64le, and hppa with kernel 6.13.0-rc7. Reviewed-by: DJ Delorie <dj@redhat.com>
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 and x86_64-gnu. When working with Linux kernels, this version of the GNU C Library requires Linux kernel version 3.2 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: aarch64*-*-linux-gnu alpha*-*-linux-gnu arc*-*-linux-gnu arm-*-linux-gnueabi csky-*-linux-gnuabiv2 hppa-*-linux-gnu i[4567]86-*-linux-gnu x86_64-*-linux-gnu Can build either x86_64 or x32 loongarch64-*-linux-gnu Hardware floating point, LE only. m68k-*-linux-gnu microblaze*-*-linux-gnu mips-*-linux-gnu mips64-*-linux-gnu or1k-*-linux-gnu powerpc-*-linux-gnu Hardware or software floating point, BE only. powerpc64*-*-linux-gnu Big-endian and little-endian. s390-*-linux-gnu s390x-*-linux-gnu riscv32-*-linux-gnu riscv64-*-linux-gnu sh[34]-*-linux-gnu sparc*-*-linux-gnu sparc64*-*-linux-gnu If you are interested in doing a port, please contact the glibc maintainers; see https://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 https://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 https://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., 1996-2015, indicating that every year in the range, inclusive, is a copyrightable year that would otherwise be listed individually.