Improve stack-top heuristic

This is needed for gcc -Os -flto on x86-64; otherwise, GC misses part
of the stack when scanning for heap roots, causing Emacs to crash
later (Bug#28213).  The problem is that Emacs's hack for getting an
address near the stack top does not work when link-time optimization
moves stack variables around.
* configure.ac (HAVE___BUILTIN_FRAME_ADDRESS): New macro.
* lib-src/make-docfile.c (DEFUN_noinline): New constant.
(write_globals, scan_c_stream): Support noinline.
* src/alloc.c (NEAR_STACK_TOP): New macro.
(SET_STACK_TOP_ADDRESS): Use it.
(flush_stack_call_func, Fgarbage_collect): Now noinline.

1 files changed, 7 insertions, 2 deletions

diff --git a/lib-src/make-docfile.c b/lib-src/make-docfile.c
index ecd6447ab78..c48f202a511 100644
--- a/lib-src/make-docfile.c
+++ b/lib-src/make-docfile.c
@@ -592,7 +592,7 @@ struct global
 };
 
 /* Bit values for FLAGS field from the above.  Applied for DEFUNs only.  */
-enum { DEFUN_noreturn = 1, DEFUN_const = 2 };
+enum { DEFUN_noreturn = 1, DEFUN_const = 2, DEFUN_noinline = 4 };
 
 /* All the variable names we saw while scanning C sources in `-g'
    mode.  */
@@ -742,6 +742,8 @@ write_globals (void)
         {
           if (globals[i].flags & DEFUN_noreturn)
             fputs ("_Noreturn ", stdout);
+          if (globals[i].flags & DEFUN_noinline)
+            fputs ("NO_INLINE ", stdout);
 
           printf ("EXFUN (%s, ", globals[i].name);
           if (globals[i].v.value == -1)
@@ -1062,7 +1064,8 @@ scan_c_stream (FILE *infile)
                    attributes: attribute1 attribute2 ...)
                (Lisp_Object arg...)
 
-             Now only 'noreturn' and 'const' attributes are used.  */
+             Now only ’const’, ’noinline’ and 'noreturn' attributes
+             are used.  */
 
           /* Advance to the end of docstring.  */
           c = getc (infile);
@@ -1108,6 +1111,8 @@ scan_c_stream (FILE *infile)
                 g->flags |= DEFUN_noreturn;
               if (strstr (input_buffer, "const"))
                 g->flags |= DEFUN_const;
+              if (strstr (input_buffer, "noinline"))
+                g->flags |= DEFUN_noinline;
             }
           continue;
         }