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| author | Paul Eggert <eggert@cs.ucla.edu> | 2015-06-24 20:10:03 -0700 |
|---|---|---|
| committer | Paul Eggert <eggert@cs.ucla.edu> | 2015-06-24 20:10:44 -0700 |
| commit | 93f4f67ba93b78e8b31e498e8ce7bce4c8298b76 (patch) | |
| tree | 788c0808926664ea23de2f903f4c233c5febf7ab /src/lisp.h | |
| parent | f230b2ff3136120a9be544a5d3a974f7087ce55b (diff) | |
| download | emacs-93f4f67ba93b78e8b31e498e8ce7bce4c8298b76.tar.gz | |
Fix GC bugs --with-wide-int and Qnil == 0
Use the same alignment for the !USE_LSB_TAG case as for the
more-typical USE_LSB_TAG case. The attempt to support arbitrary
alignments with !USE_LSB_TAG had subtle bugs in garbage collection
once we changed the representation of symbols so that Qnil == 0.
Problem reported by Eli Zaretskii (Bug#20862).
* src/alloc.c (XMALLOC_HEADER_ALIGNMENT) [XMALLOC_OVERRUN_CHECK]:
* src/alloc.c (vector_alignment, union aligned_Lisp_Symbol)
(union aligned_Lisp_Misc, maybe_lisp_pointer, pure_alloc):
Use same alignment for !USE_LSB_TAG as for USE_LSB_TAG.
* src/alloc.c (POINTERS_MIGHT_HIDE_IN_OBJECTS): Remove.
This optimization in the !USE_LSB_TAG case is no longer valid when
symbols are represented via offsets. Change the only use to
assume that pointers might hide in objects.
* src/lisp.h (alignas) [!USE_LSB_TAG]:
Require support in this case, too.
(TAG_SYMOFFSET, XSYMBOL) [!USE_LSB_TAG]: Do not shift the offset.
This is OK, because the !USE_LSB_TAG case now applies only when
Lisp_Object is wider than void *, so there's no longer any need
to shift the offset. Not shifting the offset means that
symbol representations have the same alignment as pointers,
which the GC assumes.
Diffstat (limited to 'src/lisp.h')
| -rw-r--r-- | src/lisp.h | 11 |
1 files changed, 2 insertions, 9 deletions
diff --git a/src/lisp.h b/src/lisp.h index 198f116fe02..c3289c9d700 100644 --- a/src/lisp.h +++ b/src/lisp.h @@ -278,10 +278,7 @@ error !; #endif #ifndef alignas -# define alignas(alignment) /* empty */ -# if USE_LSB_TAG -# error "USE_LSB_TAG requires alignas" -# endif +# error "alignas not defined" #endif #ifdef HAVE_STRUCT_ATTRIBUTE_ALIGNED @@ -731,9 +728,7 @@ struct Lisp_Symbol /* Yield an integer that contains a symbol tag along with OFFSET. OFFSET should be the offset in bytes from 'lispsym' to the symbol. */ -#define TAG_SYMOFFSET(offset) \ - TAG_PTR (Lisp_Symbol, \ - ((uintptr_t) (offset) >> (USE_LSB_TAG ? 0 : GCTYPEBITS))) +#define TAG_SYMOFFSET(offset) TAG_PTR (Lisp_Symbol, offset) /* XLI_BUILTIN_LISPSYM (iQwhatever) is equivalent to XLI (builtin_lisp_symbol (Qwhatever)), @@ -899,8 +894,6 @@ INLINE struct Lisp_Symbol * XSYMBOL (Lisp_Object a) { uintptr_t i = (uintptr_t) XUNTAG (a, Lisp_Symbol); - if (! USE_LSB_TAG) - i <<= GCTYPEBITS; void *p = (char *) lispsym + i; return p; } |