From 6c57d320484988e87e446e2e60ce42816bf51d53 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Mon, 1 Feb 2021 11:00:38 -0800 Subject: 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. --- NEWS | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'NEWS') diff --git a/NEWS b/NEWS index 4ac2849e23..7e535c990e 100644 --- a/NEWS +++ b/NEWS @@ -33,6 +33,11 @@ Version 2.33 Major new features: +* Add _SC_MINSIGSTKSZ and _SC_SIGSTKSZ. When _SC_SIGSTKSZ_SOURCE or + _GNU_SOURCE are defined, MINSIGSTKSZ and SIGSTKSZ are no longer + constant on Linux. MINSIGSTKSZ is redefined to sysconf(_SC_MINSIGSTKSZ) + and SIGSTKSZ is redefined to sysconf (_SC_SIGSTKSZ). + * The dynamic linker accepts the --list-tunables argument which prints all the supported tunables. This option is disable if glibc is configured with tunables disabled (--enable-tunables=no). -- cgit 1.4.1