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Avoid accessing uninitialized bool_vector words

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Although loading uninitialized works from memory and then ignoring
the result works fine on conventional architectures, it
technically has undefined behavior in C, so redo bool_vector
allocation so that the code never does that.  This can improve
performance when allocating large vectors of nil, since calloc can
clear the memory lazily.
* src/alloc.c (make_clear_bool_vector): New function,
a generalization of make_uninit_bool_vector.
(make_uninit_bool_vector): Use it.
(Fmake_bool_vector): If !INIT, rely on make_clear_bool_vector.
* src/alloc.c (Fbool_vector):
* src/fns.c (Freverse): Don’t access uninitialized bool_vector words.
This commit is contained in:
Paul Eggert 2024-07-20 00:17:14 -07:00
parent cb78b43f39
commit 79b9f05d3a
3 changed files with 30 additions and 23 deletions
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src/lisp.h
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@ -4578,6 +4578,7 @@ list4i (intmax_t a, intmax_t b, intmax_t c, intmax_t d)
return list4 (make_int (a), make_int (b), make_int (c), make_int (d));
}
extern Lisp_Object make_clear_bool_vector (EMACS_INT, bool);
extern Lisp_Object make_uninit_bool_vector (EMACS_INT);
extern Lisp_Object bool_vector_fill (Lisp_Object, Lisp_Object);
extern AVOID string_overflow (void);