Jeff et. al. > On 9 Jun 2021, at 17:23, Jeff Law via Gcc-patches <gcc-patches@gcc.gnu.org> > wrote: > On 5/25/2021 2:23 PM, Paul Eggert wrote: >> The GCC manual's documentation of -fno-trampolines was apparently >> written from an Ada point of view. However, when I read it I >> understandably mistook it to say that -fno-trampolines also works for >> C, C++, etc. It doesn't: it is silently ignored for these languages, >> and I assume for any language other than Ada. >> >> This confusion caused me to go in the wrong direction in a Gnulib >> dicussion, as I mistakenly thought that entire C apps with nested >> functions could be compiled with -fno-trampolines and then use nested >> C functions in stack overflow handlers where the alternate stack >> is allocated via malloc. I was wrong, as this won't work on common >> platforms like x86-64 where malloc yields non-executable storage. >> >> gcc/ >> * doc/invoke.texi (Code Gen Options): >> * doc/tm.texi.in (Trampolines): >> Document that -fno-trampolines and -ftrampolines work >> only with Ada. > So Martin Uecker probably has the most state on this. IIRC when we last > discussed -fno-trampolines the belief was that it could be easily made to > work independent of the language, but that it was ultimately an ABI change. > That ultimately derailed plans to use -fno-trampolines for other languages in > the immediate term.
This is correct, it’s not technically too hard to make it work for another language (I have a hack in my arm64-darwin branch that does this for gfortran). As noted for most ports it is an ABI break and thus not usable outside a such a work-around. For the record (for the arm64-darwin port in the first instance), together with some of my friends at embecosm we plan to implement a solution to the trampoline that does not require executable stack and does not require an ABI break. Perhaps such a solution will be of interest to other ports that do not want executable stack. We’re not quite ready to post the design yet - but will do so in the next few weeks (all being well). cheers Iain
