Am Montag, den 17.12.2018, 10:28 -0700 schrieb Jeff Law:
> > But the alignment increase itself on 'i386' and 'aarch64'
> > might be unacceptable. In this case, the only safe change
> > is to make the higher alignment also depend on
> > "-fno-trampolines". Would this be acceptable?
>
> Unclear at this point.
Hi Jeff,
in any case, here is another revision of this patch for
consideration which implements just this.
The lang hook is not activated for C anymore which means
that this patch is a no-op when -fno-trampolines is not
given. So the test about achieving the minimum alignment on
i386 does not fail anymore.
With -fno-trampolines the minimum alignment is increased
as needed on platforms which support descriptors.
For C and Ada (where it is the default) function
descriptors are created instead of trampolines.
If -fno-trampolines is given on platforms which do not
support descriptors a warning is given (before the flag
was silently ignored.)
I also made the existing warnings about the ABI change
more visible (similar to -freg-struct-return or similar
flags).
I consider the current behavior broken, where the flag
is a silent no-op for most languages and on some targets
while the documentation implies otherwise.
Bootstrapped and regression tested on x86.
I also tested -fno-trampolines on a project of mine which
uses nested functions and has a test suite and there it
works perfectly and removes the need for the executable stack.
Finally, this patch is a tiny and self-contained change which
could easily be reverted if there should be any unanticipated
failures.
Best,
Martin
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 4be16c15f86..8825d87b44f 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,16 @@
+2018-12-20 Martin Uecker <martin.uec...@med.uni-goettingen.de>
+
+ * common.opt (flag_trampolines): Change default.
+ * calls.c (prepare_call_address): Remove check for
+ flag_trampolines. Decision is now made in FEs.
+ * defaults.h (FUNCTION_ALIGNMENT): Add test for flag_trampolines.
+ * tree-nested.c (convert_tramp_reference_op): Likewise.
+ * toplev.c (process_options): Add warning for -fno-trampolines on
+ unsupported targets.
+ * doc/invoke.texi (-fno-trampolines): Document support for C.
+ * doc/sourcebuild.texi (target attributes): Document new
+ "notrampolines" effective target keyword.
+
2018-12-20 Vladimir Makarov <vmaka...@redhat.com>
PR target/88457
diff --git a/gcc/ada/ChangeLog b/gcc/ada/ChangeLog
index ba974cdcb03..c2f3d0db281 100644
--- a/gcc/ada/ChangeLog
+++ b/gcc/ada/ChangeLog
@@ -1,3 +1,8 @@
+2018-12-20 Martin Uecker <martin.uec...@med.uni-goettingen.de>
+
+ * gcc-interface/trans.c (Attribute_to_gnu): Add check for
+ flag_trampolines.
+
2018-12-14 Eric Botcazou <ebotca...@adacore.com>
* gcc-interface/decl.c (rm_size): Take into account the padding in
diff --git a/gcc/ada/gcc-interface/trans.c b/gcc/ada/gcc-interface/trans.c
index 620dbd3d36d..ae4139e9b84 100644
--- a/gcc/ada/gcc-interface/trans.c
+++ b/gcc/ada/gcc-interface/trans.c
@@ -2239,7 +2239,8 @@ Attribute_to_gnu (Node_Id gnat_node, tree
*gnu_result_type_p, int attribute)
if ((attribute == Attr_Access
|| attribute == Attr_Unrestricted_Access)
&& targetm.calls.custom_function_descriptors > 0
- && Can_Use_Internal_Rep (Etype (gnat_node)))
+ && Can_Use_Internal_Rep (Etype (gnat_node))
+ && flag_trampolines != 1)
FUNC_ADDR_BY_DESCRIPTOR (gnu_expr) = 1;
/* Otherwise, we need to check that we are not violating the
@@ -5050,7 +5051,8 @@ Call_to_gnu (Node_Id gnat_node, tree *gnu_result_type_p,
tree gnu_target,
/* If the access type doesn't require foreign-compatible representation,
be prepared for descriptors. */
if (targetm.calls.custom_function_descriptors > 0
- && Can_Use_Internal_Rep (Etype (Prefix (Name (gnat_node)))))
+ && Can_Use_Internal_Rep (Etype (Prefix (Name (gnat_node))))
+ && flag_trampolines != 1)
by_descriptor = true;
}
else if (Nkind (Name (gnat_node)) == N_Attribute_Reference)
diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index 6e12dda2331..71443846799 100644
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,3 +1,9 @@
+2018-12-20 Martin Uecker <martin.uec...@med.uni-goettingen.de>
+
+ * c-typeck.c (function_to_pointer_conversion): If using descriptors
+ instead of trampolines, amend function address with
+ FUNC_ADDR_BY_DESCRIPTOR and calls with ALL_EXPR_BY_DESCRIPTOR.
+
2018-12-19 Segher Boessenkool <seg...@kernel.crashing.org>
* c-parser.c (c_parser_asm_statement) <RID_CONST, RID_RESTRICT>: Give
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 1ae5ede81e6..6363dfda3b8 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -1913,7 +1913,14 @@ function_to_pointer_conversion (location_t loc, tree exp)
if (TREE_NO_WARNING (orig_exp))
TREE_NO_WARNING (exp) = 1;
- return build_unary_op (loc, ADDR_EXPR, exp, false);
+ tree r = build_unary_op (loc, ADDR_EXPR, exp, false);
+
+ if (TREE_CODE(r) == ADDR_EXPR
+ && targetm.calls.custom_function_descriptors > 0
+ && flag_trampolines == 0)
+ FUNC_ADDR_BY_DESCRIPTOR (r) = 1;
+
+ return r;
}
/* Mark EXP as read, not just set, for set but not used -Wunused
@@ -3135,6 +3142,12 @@ build_function_call_vec (location_t loc, vec<location_t>
arg_loc,
else
result = build_call_array_loc (loc, TREE_TYPE (fntype),
function, nargs, argarray);
+
+ if (TREE_CODE (result) == CALL_EXPR
+ && targetm.calls.custom_function_descriptors > 0
+ && flag_trampolines == 0)
+ CALL_EXPR_BY_DESCRIPTOR (result) = 1;
+
/* If -Wnonnull warning has been diagnosed, avoid diagnosing it again
later. */
if (warned_p && TREE_CODE (result) == CALL_EXPR)
diff --git a/gcc/calls.c b/gcc/calls.c
index e3b4ef80e51..1b977c231ea 100644
--- a/gcc/calls.c
+++ b/gcc/calls.c
@@ -230,7 +230,7 @@ prepare_call_address (tree fndecl_or_type, rtx funexp, rtx
static_chain_value,
{
/* If it's an indirect call by descriptor, generate code to perform
runtime identification of the pointer and load the descriptor. */
- if ((flags & ECF_BY_DESCRIPTOR) && !flag_trampolines)
+ if (flags & ECF_BY_DESCRIPTOR)
{
const int bit_val = targetm.calls.custom_function_descriptors;
rtx call_lab = gen_label_rtx ();
diff --git a/gcc/common.opt b/gcc/common.opt
index 45d7f6189e5..d85d77b5b91 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2546,7 +2546,7 @@ Common Report Var(flag_tracer) Optimization
Perform superblock formation via tail duplication.
ftrampolines
-Common Report Var(flag_trampolines) Init(0)
+Common Report Var(flag_trampolines) Init(-1)
For targets that normally need trampolines for nested functions, always
generate them instead of using descriptors.
diff --git a/gcc/defaults.h b/gcc/defaults.h
index 9035b333be8..66de347edef 100644
--- a/gcc/defaults.h
+++ b/gcc/defaults.h
@@ -1050,7 +1050,8 @@ see the files COPYING3 and COPYING.RUNTIME respectively.
If not, see
/* Force minimum alignment to be able to use the least significant bits
for distinguishing descriptor addresses from code addresses. */
#define FUNCTION_ALIGNMENT(ALIGN) \
- (lang_hooks.custom_function_descriptors \
+ (( lang_hooks.custom_function_descriptors \
+ || flag_trampolines == 0) \
&& targetm.calls.custom_function_descriptors > 0 \
? MAX ((ALIGN), \
2 * targetm.calls.custom_function_descriptors * BITS_PER_UNIT)\
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index ac2ee59d92c..5662abd1b97 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -14030,9 +14030,10 @@ made executable in order for the program to work
properly.
basis to let the compiler avoid generating them, if it computes that this
is safe, and replace them with descriptors. Descriptors are made up of data
only, but the generated code must be prepared to deal with them. As of this
-writing, @option{-fno-trampolines} is enabled by default only for Ada.
+writing, @option{-fno-trampolines} is supported only for C and Ada and
+enabled by default only for Ada.
-Moreover, code compiled with @option{-ftrampolines} and code compiled with
+@strong{Warning:} Code compiled with @option{-ftrampolines} and code compiled
with
@option{-fno-trampolines} are not binary compatible if nested functions are
present. This option must therefore be used on a program-wide basis and be
manipulated with extreme care.
diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi
index 29c693b9644..d645d1def92 100644
--- a/gcc/doc/sourcebuild.texi
+++ b/gcc/doc/sourcebuild.texi
@@ -2162,6 +2162,9 @@ Target supports Newlib.
GCC was configured with @code{--enable-newlib-nano-formatted-io}, which reduces
the code size of Newlib formatted I/O functions.
+@item notrampolines
+Target supports option @option{-fno-trampolines}.
+
@item pow10
Target provides @code{pow10} function.
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 33a4776b921..24f443bb26f 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2018-12-20 Martin Uecker <martin.uec...@med.uni-goettingen.de>
+
+ * gcc.dg/trampoline-2.c: New test.
+ * lib/target-supports.exp
+ (check_effective_target_notrampolines): New.
+
2018-12-20 Vladimir Makarov <vmaka...@redhat.com>
PR target/88457
diff --git a/gcc/testsuite/gcc.dg/trampoline-2.c
b/gcc/testsuite/gcc.dg/trampoline-2.c
new file mode 100644
index 00000000000..06c1cf4f647
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/trampoline-2.c
@@ -0,0 +1,23 @@
+/* test that nested function work without trampolines for -fno-trampolines */
+/* Origin: Martin Uecker <martin.uec...@med.uni-goettingen.de> */
+/* { dg-require-effective-target notrampolines } */
+/* { dg-options "-std=gnu11 -O2 -Wtrampolines -fno-trampolines" } */
+
+static int p(void) { return +1; }
+static int m(void) { return -1; }
+static int z(void) { return 0; }
+
+typedef int (*funptr_t)(void);
+
+static int A(int k, funptr_t a1, funptr_t a2, funptr_t a3, funptr_t a4,
funptr_t a5)
+{
+ int B(void) { return A(--k, B, a1, a2, a3, a4); }
+
+ return (k <= 0) ? (a4() + a5()) : (B());
+}
+
+int main(void)
+{
+ return (0 == A(5, p, m, m, p, z)) ? 0 : 1;
+}
+
diff --git a/gcc/testsuite/lib/target-supports.exp
b/gcc/testsuite/lib/target-supports.exp
index 7dec43233e0..43f9bb3891f 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -924,6 +924,14 @@ proc check_effective_target_scheduling {} {
} "-fschedule-insns"]
}
+# Return 1 if it is possible to use function descriptors instead of
trampolines, 0 otherwise.
+
+proc check_effective_target_notrampolines {} {
+ return [check_no_compiler_messages notrampolines assembly {
+ void foo (void) { }
+ } "-fno-trampolines"]
+}
+
# Return 1 if trapping arithmetic is available, 0 otherwise.
proc check_effective_target_trapping {} {
diff --git a/gcc/toplev.c b/gcc/toplev.c
index ab20cd98969..765ce347172 100644
--- a/gcc/toplev.c
+++ b/gcc/toplev.c
@@ -1698,6 +1698,12 @@ process_options (void)
flag_prefetch_loop_arrays = 0;
}
+ if (flag_trampolines == 0 && targetm.calls.custom_function_descriptors == -1)
+ {
+ warning_at (UNKNOWN_LOCATION, 0,
+ "-fno-trampolines not supported for this target");
+ }
+
/* This combination of options isn't handled for i386 targets and doesn't
make much sense anyway, so don't allow it. */
if (flag_prefetch_loop_arrays > 0 && optimize_size)
diff --git a/gcc/tree-nested.c b/gcc/tree-nested.c
index 0ad469ada49..eb9bccb7a9d 100644
--- a/gcc/tree-nested.c
+++ b/gcc/tree-nested.c
@@ -2544,7 +2544,7 @@ convert_tramp_reference_op (tree *tp, int *walk_subtrees,
void *data)
continue;
/* Decide whether to generate a descriptor or a trampoline. */
- descr = FUNC_ADDR_BY_DESCRIPTOR (t) && !flag_trampolines;
+ descr = FUNC_ADDR_BY_DESCRIPTOR (t);
if (descr)
x = lookup_descr_for_decl (i, decl, INSERT);
