On Mon, 22 May 2023, Geert Uytterhoeven wrote:
Reviewed-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> i.e. will queue as a fix in the m68k for-v6.4 branch.
Thanks Geert!
I plan to send this upstream later this week, so any additional testing would be appreciated.
If there is a userland program that needs all of its sigaltstack space, and cannot accomodate a 256 byte margin, it will be hard to find that program. Often these signal stacks are used for handling (would-be) fatal signals that may not happen in regression testing. If we fix the kernel and a failure eventually does show up in a userland program, we may be able to patch that program. Looking through Debian's codebase, which is easily searchable, I found lots of different ways to determine the signal stack size. But it's not clear to me which programs calculate it correctly. Many programs take the architecture's SIGSTKSZ or MINSIGSTKSZ or getauxval(AT_MINSIGSTKSZ) or sysconf(_SC_SIGSTKSZ), or some combination, and then apply an arbitrary safety factor. Some add a constant or apply a lower bound that may reflect the actual requirements of the signal handler. Some just use page_size(). https://sources.debian.org/src/rust-generator/0.7.1-1/src/stack/unix.rs/?hl=85#L84 https://sources.debian.org/src/ocaml/4.13.1-4/runtime/signals_nat.c/?hl=293#L289 https://sources.debian.org/src/ruby3.1/3.1.2-7/signal.c/?hl=538#L531 https://sources.debian.org/src/python3.11/3.11.2-6/Modules/faulthandler.c/?hl=1385#L1368 https://sources.debian.org/src/llvm-toolchain-9/1:9.0.1-20/llvm/lib/Support/Unix/Signals.inc/?hl=259#L250 https://sources.debian.org/src/musl/1.2.3-1/src/aio/aio.c/?hl=98#L83 https://sources.debian.org/src/libreoffice/4:7.4.5-2/external/breakpad/SIGSTKSZ.patch/?hl=4#L4 https://sources.debian.org/src/libuv1/1.44.2-1/src/unix/thread.c/?hl=168#L165 https://sources.debian.org/src/stress-ng/0.15.08-1/core-helper.c/?hl=3290#L3276 https://sources.debian.org/src/cysignals/1.11.2+ds-2/src/cysignals/implementation.c/?hl=446#L442 https://sources.debian.org/src/vim/2:9.0.1378-2/src/os_unix.c/?hl=828#L811 https://sources.debian.org/src/m4/1.4.19-3/m4/sigaltstack.m4/?hl=88#L72 https://sources.debian.org/src/varnish/7.1.1-1.1/bin/varnishd/cache/cache_main.c/?hl=342#L330 https://sources.debian.org/src/sfxr-qt/1.5.0+ds-2/debian/patches/catch2-patch/?hl=3223#L3121
