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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.
84 lines
2.8 KiB
C
84 lines
2.8 KiB
C
/* Emulate AT_MINSIGSTKSZ. Linux/x86 version.
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Copyright (C) 2020 Free Software Foundation, Inc.
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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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/* Emulate AT_MINSIGSTKSZ with XSAVE. */
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static inline void
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dl_check_minsigstacksize (const struct cpu_features *cpu_features)
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{
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/* Return if AT_MINSIGSTKSZ is provide by kernel. */
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if (GLRO(dl_minsigstacksize) != 0)
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return;
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if (cpu_features->basic.max_cpuid >= 0xd
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&& CPU_FEATURES_CPU_P (cpu_features, OSXSAVE))
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{
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/* Emulate AT_MINSIGSTKSZ. In Linux kernel, the signal frame data
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with XSAVE is composed of the following areas and laid out as:
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------------------------------
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| alignment padding |
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------------------------------
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| xsave buffer |
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------------------------------
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| fsave header (32-bit only) |
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------------------------------
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| siginfo + ucontext |
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------------------------------
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*/
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unsigned int sigframe_size;
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#ifdef __x86_64__
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/* NB: sizeof(struct rt_sigframe) + 8-byte return address in Linux
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kernel. */
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sigframe_size = 440 + 8;
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#else
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/* NB: sizeof(struct sigframe_ia32) + sizeof(struct fregs_state)) +
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4-byte return address + 3 * 4-byte arguments in Linux kernel. */
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sigframe_size = 736 + 112 + 4 + 3 * 4;
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#endif
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/* Add 15 bytes to align the stack to 16 bytes. */
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sigframe_size += 15;
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/* Make the space before xsave buffer multiple of 16 bytes. */
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sigframe_size = ALIGN_UP (sigframe_size, 16);
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/* Add (64 - 16)-byte padding to align xsave buffer at 64 bytes. */
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sigframe_size += 64 - 16;
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unsigned int eax, ebx, ecx, edx;
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__cpuid_count (0xd, 0, eax, ebx, ecx, edx);
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/* Add the size of xsave buffer. */
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sigframe_size += ebx;
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/* Add the size of FP_XSTATE_MAGIC2. */
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#define FP_XSTATE_MAGIC2 0x46505845U
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sigframe_size += sizeof (FP_XSTATE_MAGIC2);
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GLRO(dl_minsigstacksize) = sigframe_size;
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}
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else
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{
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/* NB: Default to a constant MINSIGSTKSZ. */
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_Static_assert (__builtin_constant_p (MINSIGSTKSZ),
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"MINSIGSTKSZ is constant");
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GLRO(dl_minsigstacksize) = MINSIGSTKSZ;
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}
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}
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