On Wed, Jun 9, 2021 at 11:15 AM Thomas Rodgers
<rodg...@appliantology.com> wrote:
>
> On 2021-06-09 09:23, Jeff Law via Gcc-patches 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.
> >
> > 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
>
> This patch (commit 4a0c4eaea32) is currently breaking the compilation
> with "Verify that you have permission to grant a GFDL license for all".
> It appears that tm.texi and tm.texi.in are out of sync.
I am checking in this to unbreak it:
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index 20501607716..33532f092b6 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -3828,6 +3828,7 @@ addresses. Since GCC's generic function descriptors are
not ABI-compliant, this option is typically used only on a
per-language basis (notably by Ada) or when it can otherwise be
applied to the whole program.
+
For languages other than Ada, the @code{-ftrampolines} and
@code{-fno-trampolines} options currently have no effect, and
trampolines are always generated on platforms that need them
--
H.J.
