Port to gcc -fcheck-pointer-bounds
This is a minimal port, just to get Emacs running; it does not attempt to make the pointer bounds at all tight. * src/ptr-bounds.h: New file. * src/alloc.c, src/gmalloc.c: Include it. * src/alloc.c (live_string_holding, live_cons_holding) (live_symbol_holding, live_misc_holding, garbage_collect_1) (sweep_conses, sweep_floats): * src/gmalloc.c (malloc_initialize_1, _free_internal_nolock) (_realloc_internal_nolock): Widen pointer bounds as necessary. We're in a memory allocator so this is OK. * src/lisp.h (lisp_h_XSYMBOL, make_lisp_symbol) [__CHKP__]: Do not convert from pointer to integer and back again, so that GCC does not lose track of pointer bounds. (XSYMBOL) [__CHKP__ && !USE_LSB_TAG]: Now a compile-time error. Although it's possible to support both -fcheck-pointer-bounds and --with-wide-int, it's more work; keep things simple for now. (DEFINE_LISP_SYMBOL) [__CHKP__]: Now a no-op, to avoid trouble with unbounded pointers.
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