diff options
| author | Mattias Engdegård <mattiase@acm.org> | 2023-09-18 19:16:05 +0200 |
|---|---|---|
| committer | Mattias Engdegård <mattiase@acm.org> | 2023-09-19 15:21:03 +0200 |
| commit | 321f2e1e4d4b2f209b072dc891cc89cbab19f032 (patch) | |
| tree | 8d5747df71c6936ed27e75b787460e10f6c415cd /src | |
| parent | 7be5c8f47c9df01a5accdbf954d952b9bbe5b5f0 (diff) | |
Don't use pointer arithmetic for pointer tagging (bug#65491)
This makes for safer code when tagging null pointers in particular,
since pointer arithmetic on NULL is undefined and therefore can be
assumed, by the compiler, not to occur.
* src/lisp.h (untagged_ptr): Remove.
(TAG_PTR): Cast to uintptr_t instead of untagged_ptr.
Diffstat (limited to 'src')
| -rw-r--r-- | src/lisp.h | 15 |
1 files changed, 3 insertions, 12 deletions
diff --git a/src/lisp.h b/src/lisp.h index 79ce8e5fa8e..39aa51531fe 100644 --- a/src/lisp.h +++ b/src/lisp.h @@ -919,20 +919,11 @@ verify (GCALIGNED (struct Lisp_Symbol)); #define DEFUN_ARGS_8 (Lisp_Object, Lisp_Object, Lisp_Object, Lisp_Object, \ Lisp_Object, Lisp_Object, Lisp_Object, Lisp_Object) -/* untagged_ptr represents a pointer before tagging, and Lisp_Word_tag - contains a possibly-shifted tag to be added to an untagged_ptr to - convert it to a Lisp_Word. */ +/* Lisp_Word_tag is big enough for a possibly-shifted tag, to be + added to a pointer value for conversion to a Lisp_Word. */ #if LISP_WORDS_ARE_POINTERS -/* untagged_ptr is a pointer so that the compiler knows that TAG_PTR - yields a pointer. It is char * so that adding a tag uses simple - machine addition. */ -typedef char *untagged_ptr; typedef uintptr_t Lisp_Word_tag; #else -/* untagged_ptr is an unsigned integer instead of a pointer, so that - it can be added to the possibly-wider Lisp_Word_tag type without - losing information. */ -typedef uintptr_t untagged_ptr; typedef EMACS_UINT Lisp_Word_tag; #endif @@ -942,7 +933,7 @@ typedef EMACS_UINT Lisp_Word_tag; /* An initializer for a Lisp_Object that contains TAG along with PTR. */ #define TAG_PTR(tag, ptr) \ - LISP_INITIALLY ((Lisp_Word) ((untagged_ptr) (ptr) + LISP_WORD_TAG (tag))) + LISP_INITIALLY ((Lisp_Word) ((uintptr_t) (ptr) + LISP_WORD_TAG (tag))) /* LISPSYM_INITIALLY (Qfoo) is equivalent to Qfoo except it is designed for use as an initializer, even for a constant initializer. */ |