procyberian/emacs
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Simplify pointer computation in mark_maybe_object

Browse source 
* src/alloc.c (mark_maybe_object):
Use simpler way to avoid -fsanitize=undefined false alarms,
by converting the word tag to intptr_t first.
Omit now-unnecessary runtime overflow check.
(mark_memory): Work even if UINTPTR_MAX <= INT_MAX (!).
This commit is contained in:
Paul Eggert 2020-08-03 15:21:58 -07:00
parent ca419812d3
commit a4ed198e8f
1 changed files with 7 additions and 17 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

24
src/alloc.c
View file

@ -4625,7 +4625,7 @@ mark_maybe_object (Lisp_Object obj)
#endif
int type_tag = XTYPE (obj);
intptr_t offset;
intptr_t pointer_word_tag = LISP_WORD_TAG (type_tag), offset, ipo;
switch (type_tag)
{
@ -4641,19 +4641,8 @@ mark_maybe_object (Lisp_Object obj)
break;
}
bool overflow
= INT_SUBTRACT_WRAPV (offset, LISP_WORD_TAG (type_tag), &offset);
#if !defined WIDE_EMACS_INT || USE_LSB_TAG
/* If we don't use wide integers, then `intptr_t' should always be
large enough to not overflow. Furthermore, when using the least
significant bits as tag bits, the tag is small enough to not
overflow either. */
eassert (!overflow);
#else
(void) overflow;
#endif
INT_ADD_WRAPV (offset, (intptr_t) (char *) XLP (obj), &offset);
void *po = (char *) offset;
INT_ADD_WRAPV ((intptr_t) XLP (obj), offset - pointer_word_tag, &ipo);
void *po = (void *) ipo;
/* If the pointer is in the dump image and the dump has a record
of the object starting at the place where the pointer points, we
@ -4856,7 +4845,7 @@ mark_memory (void const *start, void const *end)
for (pp = start; (void const *) pp < end; pp += GC_POINTER_ALIGNMENT)
{
char *p = *(char *const *) pp;
void *p = *(void *const *) pp;
mark_maybe_pointer (p);
/* Unmask any struct Lisp_Symbol pointer that make_lisp_symbol
@ -4864,8 +4853,9 @@ mark_memory (void const *start, void const *end)
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. */
p = (char *) ((uintptr_t) p + (uintptr_t) lispsym);
mark_maybe_pointer (p);
intptr_t ip;
INT_ADD_WRAPV ((intptr_t) p, (intptr_t) lispsym, &ip);
mark_maybe_pointer ((void *) ip);
verify (alignof (Lisp_Object) % GC_POINTER_ALIGNMENT == 0);
if (alignof (Lisp_Object) == GC_POINTER_ALIGNMENT