From a5f8ce9f1eae29f87fe13adb61bd4e15faa628a2 Mon Sep 17 00:00:00 2001
From: Po Lu
Date: Sun, 9 Mar 2025 23:02:21 +0800
Subject: Re-port to 32-bit systems without alignment primitives

* configure.ac (ALIGNOF_INT, ALIGNOF_LONG, ALIGNOF_LONG_LONG):
New variables.
(emacs_cv_alignas_unavailable): Define if alignas and structure
alignment primitives are unavailable.  In such an environment,
the MSB tagging scheme must be enabled, as must the GNU malloc.

* msdos/sed2v2.inp: Adjust correspondingly.

* src/alloc.c (union emacs_align_type): Remove types which
contain flexible array members.  The address of a field
subsequent to an aggregate with flexible array members cannot
validly be taken.
(mark_memory) [!USE_LSB_TAG && !WIDE_EMACS_INT]: Strip type bits
before scanning memory.

* src/emacs.c (main):

* src/eval.c (Fautoload_do_load):

* src/fns.c (Frequire): Rename a number of illogically named
fields.

* src/lisp.h (ALIGNOF_EMACS_INT): Define to the natural
alignment of EMACS_INT.
(IDEAL_GCALIGNMENT): New macro.
(USE_LSB_TAG): Disable if no alignment specifiers are available,
WIDE_EMACS_INT is undefined, and the natural alignment of
EMACS_INT falls short of LSB tagging's requirements.
(gflags): Rename illogically named fields and don't define them
as bitfields, which runs afoul of certain compiler issues.
(will_dump_p, will_bootstrap_p, will_dump_with_pdumper_p)
(dumped_with_pdumper_p): Adjust accordingly.

* src/pdumper.c (VM_SUPPORTED): Define to 0 when !USE_LSB_TAG.
It is better to read dump files into the heap by hand than to be
supplied with an address that is not representable.
(_dump_object_start_pseudovector): Rename to
dump_object_start_pseudovector, to avoid encroaching on reserved
names.
(START_DUMP_PVEC): Adjust correspondingly.
(dump_mmap_contiguous_vm): Preserve errno around failure
cleanup.
(dump_bitset_bit_set_p): Work around certain compiler issues.
(pdumper_load) [!USE_LSB_TAG]: Reject dump file allocations
that are not representable as Lisp_Objects.

Tested on i386-unknown-solaris2.10, sparc-sun-solaris2.10.
---
 src/alloc.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

(limited to 'src/alloc.c')

diff --git a/src/alloc.c b/src/alloc.c
index 7fa05e54202..c0d68e6c964 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -150,8 +150,6 @@ union emacs_align_type
 {
   struct frame frame;
   struct Lisp_Bignum Lisp_Bignum;
-  struct Lisp_Bool_Vector Lisp_Bool_Vector;
-  struct Lisp_Char_Table Lisp_Char_Table;
   struct Lisp_CondVar Lisp_CondVar;
   struct Lisp_Finalizer Lisp_Finalizer;
   struct Lisp_Float Lisp_Float;
@@ -160,21 +158,25 @@ union emacs_align_type
   struct Lisp_Misc_Ptr Lisp_Misc_Ptr;
   struct Lisp_Mutex Lisp_Mutex;
   struct Lisp_Overlay Lisp_Overlay;
-  struct Lisp_Sub_Char_Table Lisp_Sub_Char_Table;
   struct Lisp_Subr Lisp_Subr;
   struct Lisp_Sqlite Lisp_Sqlite;
   struct Lisp_User_Ptr Lisp_User_Ptr;
-  struct Lisp_Vector Lisp_Vector;
   struct terminal terminal;
   struct thread_state thread_state;
   struct window window;
 
   /* Omit the following since they would require including process.h
-     etc.  In practice their alignments never exceed that of the
-     structs already listed.  */
+     etc, or because they are defined with flexible array members, which
+     are rejected by some C99 compilers when this union subsequently
+     appears in an `alignof' expression.  In practice their alignments
+     never exceed that of the structs already listed.  */
 #if 0
+  struct Lisp_Bool_Vector Lisp_Bool_Vector;
+  struct Lisp_Char_Table Lisp_Char_Table;
+  struct Lisp_Sub_Char_Table Lisp_Sub_Char_Table;
   struct Lisp_Module_Function Lisp_Module_Function;
   struct Lisp_Process Lisp_Process;
+  struct Lisp_Vector Lisp_Vector;
   struct save_window_data save_window_data;
   struct scroll_bar scroll_bar;
   struct xwidget_view xwidget_view;
@@ -5167,14 +5169,20 @@ mark_memory (void const *start, void const *end)
   for (pp = start; (void const *) pp < end; pp += GC_POINTER_ALIGNMENT)
     {
       void *p = *(void *const *) pp;
+      intptr_t ip;
+
+#if !USE_LSB_TAG && !defined WIDE_EMACS_INT
+      ip = (intptr_t) p;
+      mark_maybe_pointer ((void *) (ip & VALMASK), false);
+#else /* USE_LSB_TAG || WIDE_EMACS_INT */
       mark_maybe_pointer (p, false);
+#endif /* USE_LSB_TAG || WIDE_EMACS_INT */
 
       /* Unmask any struct Lisp_Symbol pointer that make_lisp_symbol
 	 previously disguised by adding the address of 'lispsym'.
 	 On a host with 32-bit pointers and 64-bit Lisp_Objects,
 	 a Lisp_Object might be split into registers saved into
 	 non-adjacent words and P might be the low-order word's value.  */
-      intptr_t ip;
       ckd_add (&ip, (intptr_t) p, (intptr_t) lispsym);
       mark_maybe_pointer ((void *) ip, true);
     }
-- 
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