0From: Alexandre Oliva <oliva@adacore.com>

strub: introduce STACK_ADDRESS_OFFSET

Since STACK_POINTER_OFFSET is not necessarily at the boundary between
caller- and callee-owned stack, as desired by
__builtin_stack_address(), and using it as if it were or not causes
problems, introduce a new macro so that ports can define it suitably,
without modifying STACK_POINTER_OFFSET.


for  gcc/ChangeLog

	PR middle-end/112917
	PR middle-end/113100
	* builtins.cc (expand_builtin_stack_address): Use
	STACK_ADDRESS_OFFSET.
	* doc/extend.texi (__builtin_stack_address): Adjust.
	* config/sparc/sparc.h (STACK_ADDRESS_OFFSET): Define.
	* doc/tm.texi.in (STACK_ADDRESS_OFFSET): Document.
	* doc/tm.texi: Rebuilt.

3 files changed, 59 insertions, 1 deletions

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index f0d02c9..142e41a 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -12799,7 +12799,7 @@ situations.
 
 @deftypefn {Built-in Function} {void *} __builtin_stack_address ()
 This function returns the stack pointer register, offset by
-@code{STACK_POINTER_OFFSET}.
+@code{STACK_ADDRESS_OFFSET} if that's defined.
 
 Conceptually, the returned address returned by this built-in function is
 the boundary between the stack area allocated for use by its caller, and
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 69ae63c..c8b8b12 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -3456,6 +3456,35 @@ or type, otherwise return false.  The default implementation always returns
 true.
 @end deftypefn
 
+@defmac STACK_ADDRESS_OFFSET
+Offset from the stack pointer register to the boundary address between
+the stack area claimed by an active function, and stack ranges that
+could get clobbered if it called another function.  It should NOT
+encompass any stack red zone, that is used in leaf functions.
+
+This value is added to the stack pointer register to compute the address
+returned by @code{__builtin_stack_address}, and this is its only use.
+If this macro is not defined, no offset is added.  Defining it like
+@code{STACK_POINTER_OFFSET} may be appropriate for many machines, but
+not all.
+
+On SPARC, for example, the register save area is *not* considered active
+or used by the active function, but rather as akin to the area in which
+call-preserved registers are saved by callees, so the stack address is
+above that area, even though the (unbiased) stack pointer points below
+it.  This enables @code{__strub_leave} to clear what would otherwise
+overlap with its own register save area.
+
+On PowerPC, @code{STACK_POINTER_OFFSET} also reserves space for a save
+area, but that area is used by the caller rather than the callee, so the
+boundary address is below it.
+
+If the address is computed too high or too low, parts of a stack range
+that should be scrubbed may be left unscrubbed, scrubbing may corrupt
+active portions of the stack frame, and stack ranges may be
+doubly-scrubbed by caller and callee.
+@end defmac
+
 @defmac TARGET_STRUB_USE_DYNAMIC_ARRAY
 If defined to nonzero, @code{__strub_leave} will allocate a dynamic
 array covering the stack range that needs scrubbing before clearing it.
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index 21343d4..658e1e6 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -2688,6 +2688,35 @@ may reduce the size of debug information on some ports.
 
 @hook TARGET_HAVE_STRUB_SUPPORT_FOR
 
+@defmac STACK_ADDRESS_OFFSET
+Offset from the stack pointer register to the boundary address between
+the stack area claimed by an active function, and stack ranges that
+could get clobbered if it called another function.  It should NOT
+encompass any stack red zone, that is used in leaf functions.
+
+This value is added to the stack pointer register to compute the address
+returned by @code{__builtin_stack_address}, and this is its only use.
+If this macro is not defined, no offset is added.  Defining it like
+@code{STACK_POINTER_OFFSET} may be appropriate for many machines, but
+not all.
+
+On SPARC, for example, the register save area is *not* considered active
+or used by the active function, but rather as akin to the area in which
+call-preserved registers are saved by callees, so the stack address is
+above that area, even though the (unbiased) stack pointer points below
+it.  This enables @code{__strub_leave} to clear what would otherwise
+overlap with its own register save area.
+
+On PowerPC, @code{STACK_POINTER_OFFSET} also reserves space for a save
+area, but that area is used by the caller rather than the callee, so the
+boundary address is below it.
+
+If the address is computed too high or too low, parts of a stack range
+that should be scrubbed may be left unscrubbed, scrubbing may corrupt
+active portions of the stack frame, and stack ranges may be
+doubly-scrubbed by caller and callee.
+@end defmac
+
 @defmac TARGET_STRUB_USE_DYNAMIC_ARRAY
 If defined to nonzero, @code{__strub_leave} will allocate a dynamic
 array covering the stack range that needs scrubbing before clearing it.