[PULL,v2,05/15] tcg: Mark tcg helpers noinline to avoid an issue with LTO

Commit Message

Richard Henderson Jan. 24, 2023, 2:04 a.m. UTC

Marking helpers __attribute__((noinline)) prevents an issue
with GCC's ipa-split pass under --enable-lto.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1454
Reviewed-by: Philippe Mathieu-Daudé <[e-mail]>
Tested-by: Idan Horowitz <[e-mail]>
Signed-off-by: Richard Henderson <[e-mail]>
---
 include/exec/helper-proto.h | 32 ++++++++++++++++++++++++--------
 1 file changed, 24 insertions(+), 8 deletions(-)

Patch

diff --git a/include/exec/helper-proto.h b/include/exec/helper-proto.h
index c4b1bda632..7a3f04b58c 100644
--- a/include/exec/helper-proto.h
+++ b/include/exec/helper-proto.h
@@ -6,34 +6,49 @@ 
 
 #include "exec/helper-head.h"
 
+/*
+ * Work around an issue with --enable-lto, in which GCC's ipa-split pass
+ * decides to split out the noreturn code paths that raise an exception,
+ * taking the __builtin_return_address() along into the new function,
+ * where it no longer computes a value that returns to TCG generated code.
+ * Despite the name, the noinline attribute affects splitter, so this
+ * prevents the optimization in question.  Given that helpers should not
+ * otherwise be called directly, this should have any other visible effect.
+ *
+ * See https://gitlab.com/qemu-project/qemu/-/issues/1454
+ */
+#define DEF_HELPER_ATTR  __attribute__((noinline))
+
 #define DEF_HELPER_FLAGS_0(name, flags, ret) \
-dh_ctype(ret) HELPER(name) (void);
+dh_ctype(ret) HELPER(name) (void) DEF_HELPER_ATTR;
 
 #define DEF_HELPER_FLAGS_1(name, flags, ret, t1) \
-dh_ctype(ret) HELPER(name) (dh_ctype(t1));
+dh_ctype(ret) HELPER(name) (dh_ctype(t1)) DEF_HELPER_ATTR;
 
 #define DEF_HELPER_FLAGS_2(name, flags, ret, t1, t2) \
-dh_ctype(ret) HELPER(name) (dh_ctype(t1), dh_ctype(t2));
+dh_ctype(ret) HELPER(name) (dh_ctype(t1), dh_ctype(t2)) DEF_HELPER_ATTR;
 
 #define DEF_HELPER_FLAGS_3(name, flags, ret, t1, t2, t3) \
-dh_ctype(ret) HELPER(name) (dh_ctype(t1), dh_ctype(t2), dh_ctype(t3));
+dh_ctype(ret) HELPER(name) (dh_ctype(t1), dh_ctype(t2), \
+                            dh_ctype(t3)) DEF_HELPER_ATTR;
 
 #define DEF_HELPER_FLAGS_4(name, flags, ret, t1, t2, t3, t4) \
 dh_ctype(ret) HELPER(name) (dh_ctype(t1), dh_ctype(t2), dh_ctype(t3), \
-                                   dh_ctype(t4));
+                            dh_ctype(t4)) DEF_HELPER_ATTR;
 
 #define DEF_HELPER_FLAGS_5(name, flags, ret, t1, t2, t3, t4, t5) \
 dh_ctype(ret) HELPER(name) (dh_ctype(t1), dh_ctype(t2), dh_ctype(t3), \
-                            dh_ctype(t4), dh_ctype(t5));
+                            dh_ctype(t4), dh_ctype(t5)) DEF_HELPER_ATTR;
 
 #define DEF_HELPER_FLAGS_6(name, flags, ret, t1, t2, t3, t4, t5, t6) \
 dh_ctype(ret) HELPER(name) (dh_ctype(t1), dh_ctype(t2), dh_ctype(t3), \
-                            dh_ctype(t4), dh_ctype(t5), dh_ctype(t6));
+                            dh_ctype(t4), dh_ctype(t5), \
+                            dh_ctype(t6)) DEF_HELPER_ATTR;
 
 #define DEF_HELPER_FLAGS_7(name, flags, ret, t1, t2, t3, t4, t5, t6, t7) \
 dh_ctype(ret) HELPER(name) (dh_ctype(t1), dh_ctype(t2), dh_ctype(t3), \
                             dh_ctype(t4), dh_ctype(t5), dh_ctype(t6), \
-                            dh_ctype(t7));
+                            dh_ctype(t7)) DEF_HELPER_ATTR;
 
 #define IN_HELPER_PROTO
 
@@ -51,5 +66,6 @@  dh_ctype(ret) HELPER(name) (dh_ctype(t1), dh_ctype(t2), dh_ctype(t3), \
 #undef DEF_HELPER_FLAGS_5
 #undef DEF_HELPER_FLAGS_6
 #undef DEF_HELPER_FLAGS_7
+#undef DEF_HELPER_ATTR
 
 #endif /* HELPER_PROTO_H */