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gnat_rm.texi: Document the new behavior regarding trampolines.

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2008-05-27  Bob Duff  <duff@adacore.com>

	* gnat_rm.texi:
	Document the new behavior regarding trampolines.

From-SVN: r136017
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Bob Duff 2008-05-27 13:55:11 +02:00 committed by Arnaud Charlet
parent a38ff9b14f
commit 65d0beb0e1
1 changed files with 12 additions and 0 deletions
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gcc/ada/gnat_rm.texi
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@ -8370,6 +8370,7 @@ of composite objects and the Max/Min attributes.
@item No_Implicit_Dynamic_Code
@findex No_Implicit_Dynamic_Code
@cindex trampoline
This restriction prevents the compiler from building ``trampolines''.
This is a structure that is built on the stack and contains dynamic
code to be executed at run time. On some targets, a trampoline is
@ -8379,6 +8380,17 @@ nested task bodies; primitive operations of nested tagged types.
Trampolines do not work on machines that prevent execution of stack
data. For example, on windows systems, enabling DEP (data execution
protection) will cause trampolines to raise an exception.
Trampolines are also quite slow at run time.
On many targets, trampolines have been largely eliminated. Look at the
version of system.ads for your target --- if it has
Always_Compatible_Rep equal to False, then trampolines are largely
eliminated. In particular, a trampoline is built for the following
features: @code{Address} of a nested subprogram;
@code{Access} or @code{Unrestricted_Access} of a nested subprogram,
but only if pragma Favor_Top_Level applies, or the access type has a
foreign-language convention; primitive operations of nested tagged
types.
@item No_Implicit_Loops
@findex No_Implicit_Loops