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.
The patch is fine, I just wanted to give you a bit of background on the
state. I'll go ahead and commit it for you.
Jeff
