>From f9e2b20a12a230efa30f1d479563ae07d276a94b Mon Sep 17 00:00:00 2001 From: Paul Eggert Date: Wed, 30 Sep 2020 13:50:36 -0700 Subject: [PATCH 2/3] c-stack: stop using SIGSTKSZ MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit It’s been proposed to stop making SIGSTKSZ an integer constant: https://sourceware.org/pipermail/libc-alpha/2020-September/118028.html Also, using SIGSTKSZ in #if did not conform to current POSIX. Also, avoiding SIGSTKSZ makes the code simpler and easier to grok. * lib/c-stack.c (SIGSTKSZ): Remove. (alternate_signal_stack): Now a 64 KiB array, for simplicity. All uses changed. --- ChangeLog | 9 +++++++++ lib/c-stack.c | 42 ++++++++++++++++++------------------------ lib/c-stack.h | 2 +- 3 files changed, 28 insertions(+), 25 deletions(-) diff --git a/ChangeLog b/ChangeLog index 76a76fbc4..7f54b7860 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,5 +1,14 @@ 2020-10-03 Paul Eggert + c-stack: stop using SIGSTKSZ + It’s been proposed to stop making SIGSTKSZ an integer constant: + https://sourceware.org/pipermail/libc-alpha/2020-September/118028.html + Also, using SIGSTKSZ in #if did not conform to current POSIX. + Also, avoiding SIGSTKSZ makes the code simpler and easier to grok. + * lib/c-stack.c (SIGSTKSZ): Remove. + (alternate_signal_stack): Now a 64 KiB array, for simplicity. + All uses changed. + c-stack: fix libsigsegv typo Problem reported by Bruno Haible in: https://lists.gnu.org/r/bug-gnulib/2020-09/msg00175.html diff --git a/lib/c-stack.c b/lib/c-stack.c index 80ebcbf00..cf0fe8da0 100644 --- a/lib/c-stack.c +++ b/lib/c-stack.c @@ -70,15 +70,6 @@ typedef struct sigaltstack stack_t; #if USE_LIBSIGSEGV # include -/* libsigsegv 2.6 through 2.8 have a bug where some architectures use - more than the Linux default of an 8k alternate stack when deciding - if a fault was caused by stack overflow. */ -# if LIBSIGSEGV_VERSION <= 0x0208 && SIGSTKSZ < 16384 -# undef SIGSTKSZ -# endif -#endif -#ifndef SIGSTKSZ -# define SIGSTKSZ 16384 #endif #include "exitfail.h" @@ -95,6 +86,16 @@ typedef struct sigaltstack stack_t; # endif #endif +/* Storage for the alternate signal stack. + 64 KiB is not too large for Gnulib-using apps, and is large enough + for all known platforms. Smaller sizes may run into trouble. + For example, libsigsegv 2.6 through 2.8 have a bug where some + architectures use more than the Linux default of an 8 KiB alternate + stack when deciding if a fault was caused by stack overflow. */ +static max_align_t alternate_signal_stack[(64 * 1024 + + sizeof (max_align_t) - 1) + / sizeof (max_align_t)]; + /* The user-specified action to take when a SEGV-related program error or stack overflow occurs. */ static _GL_ASYNC_SAFE void (* volatile segv_action) (int); @@ -133,7 +134,7 @@ die (int signo) size_t prognamelen = strlen (progname); size_t messagelen = strlen (message); static char const separator[] = {':', ' '}; - char buf[SIGSTKSZ / 16 + sizeof separator]; + char buf[sizeof alternate_signal_stack / 16 + sizeof separator]; ptrdiff_t buflen; if (prognamelen + messagelen < sizeof buf - sizeof separator) { @@ -159,13 +160,6 @@ die (int signo) abort (); } -/* Storage for the alternate signal stack. */ -static union -{ - char buffer[SIGSTKSZ]; - max_align_t align; -} alternate_signal_stack; - static _GL_ASYNC_SAFE void null_action (int signo _GL_UNUSED) { @@ -230,8 +224,8 @@ c_stack_action (_GL_ASYNC_SAFE void (*action) (int)) /* Always install the overflow handler. */ if (stackoverflow_install_handler (overflow_handler, - alternate_signal_stack.buffer, - sizeof alternate_signal_stack.buffer)) + alternate_signal_stack, + sizeof alternate_signal_stack)) { errno = ENOTSUP; return -1; @@ -323,14 +317,14 @@ c_stack_action (_GL_ASYNC_SAFE void (*action) (int)) { stack_t st; st.ss_flags = 0; + st.ss_sp = alternate_signal_stack; + st.ss_size = sizeof alternate_signal_stack; # if SIGALTSTACK_SS_REVERSED /* Irix mistakenly treats ss_sp as the upper bound, rather than lower bound, of the alternate stack. */ - st.ss_sp = alternate_signal_stack.buffer + SIGSTKSZ - sizeof (void *); - st.ss_size = sizeof alternate_signal_stack.buffer - sizeof (void *); -# else - st.ss_sp = alternate_signal_stack.buffer; - st.ss_size = sizeof alternate_signal_stack.buffer; + st.ss_size -= sizeof (void *); + char *ss_sp = st.ss_sp; + st.ss_sp = ss_sp + st.ss_size; # endif int r = sigaltstack (&st, NULL); if (r != 0) diff --git a/lib/c-stack.h b/lib/c-stack.h index a11fa3123..a119ef29e 100644 --- a/lib/c-stack.h +++ b/lib/c-stack.h @@ -34,7 +34,7 @@ A null ACTION acts like an action that does nothing. ACTION must be async-signal-safe. ACTION together with its callees - must not require more than SIGSTKSZ bytes of stack space. Also, + must not require more than 64 KiB of stack space. Also, ACTION should not call longjmp, because this implementation does not guarantee that it is safe to return to the original stack. -- 2.25.1