glibc/bits/sigstksz.h

/* Definition of MINSIGSTKSZ.  Generic version.
   Copyright (C) 2020 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#ifndef _SIGNAL_H
# error "Never include <bits/sigstksz.h> directly; use <signal.h> instead."
#endif
sysconf: Add _SC_MINSIGSTKSZ/_SC_SIGSTKSZ [BZ #20305] Add _SC_MINSIGSTKSZ for the minimum signal stack size derived from AT_MINSIGSTKSZ, which is the minimum number of bytes of free stack space required in order to gurantee successful, non-nested handling of a single signal whose handler is an empty function, and _SC_SIGSTKSZ which is the suggested minimum number of bytes of stack space required for a signal stack. If AT_MINSIGSTKSZ isn't available, sysconf (_SC_MINSIGSTKSZ) returns MINSIGSTKSZ. On Linux/x86 with XSAVE, the signal frame used by kernel is composed of the following areas and laid out as: ------------------------------ \| alignment padding \| ------------------------------ \| xsave buffer \| ------------------------------ \| fsave header (32-bit only) \| ------------------------------ \| siginfo + ucontext \| ------------------------------ Compute AT_MINSIGSTKSZ value as size of xsave buffer + size of fsave header (32-bit only) + size of siginfo and ucontext + alignment padding. If _SC_SIGSTKSZ_SOURCE or _GNU_SOURCE are defined, MINSIGSTKSZ and SIGSTKSZ are redefined as /* Default stack size for a signal handler: sysconf (SC_SIGSTKSZ). / # undef SIGSTKSZ # define SIGSTKSZ sysconf (_SC_SIGSTKSZ) / Minimum stack size for a signal handler: SIGSTKSZ. */ # undef MINSIGSTKSZ # define MINSIGSTKSZ SIGSTKSZ Compilation will fail if the source assumes constant MINSIGSTKSZ or SIGSTKSZ. The reason for not simply increasing the kernel's MINSIGSTKSZ #define (apart from the fact that it is rarely used, due to glibc's shadowing definitions) was that userspace binaries will have baked in the old value of the constant and may be making assumptions about it. For example, the type (char [MINSIGSTKSZ]) changes if this #define changes. This could be a problem if an newly built library tries to memcpy() or dump such an object defined by and old binary. Bounds-checking and the stack sizes passed to things like sigaltstack() and makecontext() could similarly go wrong. 2021-02-01 19:00:38 +00:00			`/* Definition of MINSIGSTKSZ. Generic version.`
			`Copyright (C) 2020 Free Software Foundation, Inc.`
			`This file is part of the GNU C Library.`

			`The GNU C Library is free software; you can redistribute it and/or`
			`modify it under the terms of the GNU Lesser General Public`
			`License as published by the Free Software Foundation; either`
			`version 2.1 of the License, or (at your option) any later version.`

			`The GNU C Library is distributed in the hope that it will be useful,`
			`but WITHOUT ANY WARRANTY; without even the implied warranty of`
			`MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU`
			`Lesser General Public License for more details.`

			`You should have received a copy of the GNU Lesser General Public`
			`License along with the GNU C Library; if not, see`
			`<https://www.gnu.org/licenses/>. */`

			`#ifndef _SIGNAL_H`
			`# error "Never include <bits/sigstksz.h> directly; use <signal.h> instead."`
			`#endif`