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.
---
gcc/doc/invoke.texi | 5 +++++
gcc/doc/tm.texi.in | 4 ++++
2 files changed, 9 insertions(+)
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 5cd4e2d993c..b55bbf3e424 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -16646,6 +16646,11 @@ Moreover, code compiled with @option{-ftrampolines}
and code compiled with
present. This option must therefore be used on a program-wide basis and be
manipulated with extreme care.
+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
+for nested functions.
+
@item -fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]}
@opindex fvisibility
Set the default ELF image symbol visibility to the specified option---all
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index d9fbbe20e6f..20501607716 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -3828,6 +3828,10 @@ 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
+for nested functions.
Define the following hook if your backend either implements ABI-specified
descriptor support, or can use GCC's generic descriptor implementation
--
2.31.1
