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6c57d32048
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.
122 lines
3.1 KiB
C
122 lines
3.1 KiB
C
/* Get file-specific information about a file. Linux version.
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Copyright (C) 2003-2021 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <assert.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <stdlib.h>
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#include <sysdep.h>
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#include <time.h>
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#include <unistd.h>
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#include <sys/resource.h>
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#include <sys/param.h>
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#include <not-cancel.h>
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#include <ldsodefs.h>
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#include <sysconf-sigstksz.h>
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/* Legacy value of ARG_MAX. The macro is now not defined since the
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actual value varies based on the stack size. */
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#define legacy_ARG_MAX 131072
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static long int posix_sysconf (int name);
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/* Get the value of the system variable NAME. */
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long int
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__sysconf (int name)
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{
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const char *procfname = NULL;
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switch (name)
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{
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case _SC_MONOTONIC_CLOCK:
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case _SC_CPUTIME:
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case _SC_THREAD_CPUTIME:
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return _POSIX_VERSION;
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case _SC_ARG_MAX:
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{
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struct rlimit rlimit;
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/* Use getrlimit to get the stack limit. */
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if (__getrlimit (RLIMIT_STACK, &rlimit) == 0)
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return MAX (legacy_ARG_MAX, rlimit.rlim_cur / 4);
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return legacy_ARG_MAX;
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}
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case _SC_NGROUPS_MAX:
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/* Try to read the information from the /proc/sys/kernel/ngroups_max
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file. */
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procfname = "/proc/sys/kernel/ngroups_max";
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break;
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case _SC_SIGQUEUE_MAX:
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{
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struct rlimit rlimit;
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if (__getrlimit (RLIMIT_SIGPENDING, &rlimit) == 0)
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return rlimit.rlim_cur;
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/* The /proc/sys/kernel/rtsig-max file contains the answer. */
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procfname = "/proc/sys/kernel/rtsig-max";
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}
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break;
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case _SC_MINSIGSTKSZ:
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assert (GLRO(dl_minsigstacksize) != 0);
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return GLRO(dl_minsigstacksize);
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case _SC_SIGSTKSZ:
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return sysconf_sigstksz ();
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default:
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break;
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}
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if (procfname != NULL)
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{
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int fd = __open_nocancel (procfname, O_RDONLY | O_CLOEXEC);
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if (fd != -1)
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{
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/* This is more than enough, the file contains a single integer. */
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char buf[32];
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ssize_t n;
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n = TEMP_FAILURE_RETRY (__read_nocancel (fd, buf, sizeof (buf) - 1));
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__close_nocancel_nostatus (fd);
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if (n > 0)
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{
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/* Terminate the string. */
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buf[n] = '\0';
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char *endp;
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long int res = strtol (buf, &endp, 10);
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if (endp != buf && (*endp == '\0' || *endp == '\n'))
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return res;
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}
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}
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}
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return posix_sysconf (name);
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}
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/* Now the POSIX version. */
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#undef __sysconf
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#define __sysconf static posix_sysconf
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#include <sysdeps/posix/sysconf.c>
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