[adding bug-gnulib] On 3/6/21 12:50 PM, Bruno Haible wrote: > Hi, > > Carol Bouchard wrote in > <https://lists.gnu.org/archive/html/bug-m4/2021-03/msg00000.html>: >> A change that was introduced is the >> #define SIGSTKSZ is no longer a statically defined variable. It's value can >> only be determined at run time. >> >> # define SIGSTKSZ sysconf (_SC_SIGSTKSZ) > > This is invalid. POSIX:2018 [1] defines two lists of macros: > > 1) "The <signal.h> header shall define the following macros which shall > expand to integer constant expressions that need not be usable in > #if preprocessing directives:" > > 2) "The <signal.h> header shall also define the following symbolic > constants:" > > SIGSTKSZ is in the second list. This implies that it must expand to a constant > and that it must be usable in #if preprocessing directives. > > Besides being invalid, it is also not needed. The alternate signal stack > needs to be dimensioned according to the CPU and ABI that is in use. For > example, > SPARC processors tend to use much more stack space than x86 per function > invocation. Similarly, 64-bit execution on a bi-arch CPU tends to use more > stack > space than 32-bit execution, because return addresses and other pointers are > 64-bit vs. 32-bit large. But once you have fixed the CPU and the ABI, there is > no ambiguity any more. > >> This affects m4 code since the code assumes a statically defined variable >> which >> can be determined at preprocessor time. > > POSIX guarantees this assumption.
Only when sticking strictly to POSIX. Reading the glibc NEWS more closely, * 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). which means you only have a non-constant SIGSTKSZ when _explicitly_ asking for non-POSIX extensions by setting _GNU_SOURCE; but since most gnulib projects (including m4) indeed request _GNU_SOURCE, we can no longer rely on the POSIX definition. > >> Please advise how I can get past this. > > Fix your <signal.h>. We're going to need to fix gnulib instead, and then release an updated m4 built with a newer gnulib. > > Bruno > > [1] https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/signal.h.html > > -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
