Eli Zaretskii schrieb am Di., 3. Okt. 2017 um 17:32 Uhr: > > > > > > +static Lisp_Object > > > > +internal_catch_all_1 (Lisp_Object (*function) (void *), void > *argument) > > > > > > Can you tell why you needed this (and the similar internal_catch_all)? > > > Is that only because the callbacks could signal an error, or is there > > > another reason? If the former, I'd prefer to simplify the code and > > > its maintenance by treating the error condition in a less drastic > > > manner, and avoiding the call to xsignal. > > > > The callbacks (especially insert and before-/after-change-hook) can exit > > nonlocally, but these nonlocal exits may not escape the Jansson callback. > > Therefore all nonlocal exits must be caught here. > > Why can't you use record_unwind_protect, as we normally do in these > situations? > How would that help? record_unwind_protect can't stop nonlocal exits. > > > > > +static _GL_ARG_NONNULL ((2)) Lisp_Object > > > > +lisp_to_json_toplevel_1 (Lisp_Object lisp, json_t **json) > > > > +{ > > > > + if (VECTORP (lisp)) > > > > + { > > > > + ptrdiff_t size = ASIZE (lisp); > > > > + eassert (size >= 0); > > > > + if (size > SIZE_MAX) > > > > + xsignal1 (Qoverflow_error, build_string ("vector is too > long")); > > > > > > I think this error text is too vague. Can we come up with something > > > that describes the problem more accurately? > > > > Maybe, but it's probably not worth it because I don't think we have many > > architectures where PTRDIFF_MAX > SIZE_MAX. > > Then why do we punish all the platforms with this runtime check? > If you think this cannot happen we can turn it into a runtime or compile-time assertion. > > > > And btw, how can size be greater than SIZE_MAX in this case? This is > > > a valid Lisp object, isn't it? (There are more such tests in the > > > patch, e.g. in lisp_to_json, and I think they, too, are redundant.) > > > > Depends on the range of ptrdiff_t and size_t. IIUC nothing in the C > > standard guarantees PTRDIFF_MAX <= SIZE_MAX. > > I wasn't talking about PTRDIFF_MAX, I was talking about 'size', which > is the number of bytes in a Lisp string. Since that Lisp string is a > valid Lisp object, how can its size be greater than SIZE_MAX? I don't > think there's a way of creating such a Lisp string in Emacs, because > functions that allocate memory for strings will prevent that. > Then I think we should at least add an assertion to document this. > > > > > + *json = json_check (json_array ()); > > > > + ptrdiff_t count = SPECPDL_INDEX (); > > > > + record_unwind_protect_ptr (json_release_object, json); > > > > + for (ptrdiff_t i = 0; i < size; ++i) > > > > + { > > > > + int status > > > > + = json_array_append_new (*json, lisp_to_json (AREF > (lisp, > > > i))); > > > > + if (status == -1) > > > > + json_out_of_memory (); > > > > + eassert (status == 0); > > > > + } > > > > + eassert (json_array_size (*json) == size); > > > > + clear_unwind_protect (count); > > > > + return unbind_to (count, Qnil); > > > > > > This, too, sounds more complex than it should: you record > > > unwind-protect just so lisp_to_json's subroutines could signal an > > > error due to insufficient memory, right? Why can't we have the > > > out-of-memory check only inside this loop, which you already do, and > > > avoid the checks on lower levels (which undoubtedly cost us extra > > > cycles)? What do those extra checks in json_check buy us? the errors > > > they signal are no more informative than the one in the loop, AFAICT. > > > > I don't understand what you mean. We need to check the return values of > all > > functions if we want to to use them later. > > Yes, but what problems can cause these return value to be invalid? > AFAICT, only out-of-memory conditions, and that can be checked only > once, there's no need to check every single allocation, because once > an allocation fails, all the rest will too. > But if the first succeeds, the second can still fail, so we do need to check all of them. > > > > > +static Lisp_Object > > > > +json_insert (void *data) > > > > +{ > > > > + const struct json_buffer_and_size *buffer_and_size = data; > > > > + if (buffer_and_size->size > PTRDIFF_MAX) > > > > + xsignal1 (Qoverflow_error, build_string ("buffer too large")); > > > > + insert (buffer_and_size->buffer, buffer_and_size->size); > > > > > > I don't think we need this test here, as 'insert' already has the > > > equivalent test in one of its subroutines. > > > > It can't, because it takes the byte length as ptrdiff_t. We need to check > > before whether the size is actually in the valid range of ptrdiff_t. > > I'm sorry, but I don't see why we should support such exotic > situations only for this one feature. In all other cases we use > either ptrdiff_t type or EMACS_INT type, and these issues disappear > then. Trying to support the SIZE_MAX > PTRDIFF_MAX situation causes > the code to be much more complicated, harder to maintain, and more > expensive at run time than it should be. We can't avoid these checks. The API returns size_t, so we can only assume that the numbers are in the valid range of size_t, which is larger than the ones for positive ptrdiff_t's. There's no way around this. > I'm not even sure there are > such platforms out there that Emacs supports, All platforms that I know of have SIZE_MAX > PTRDIFF_MAX. > but if there are, we > already have a gazillion problems like that all over our code. Just because other parts of the codebase are buggy doesn't mean we need to introduce more bugs in new code. > I > object to having such code just for this reason, sorry. > We can't avoid it. > > > > > + case JSON_INTEGER: > > > > + { > > > > + json_int_t value = json_integer_value (json); > > > > + if (FIXNUM_OVERFLOW_P (value)) > > > > + xsignal1 (Qoverflow_error, > > > > + build_string ("JSON integer is too large")); > > > > + return make_number (value); > > > > > > This overflow test is also redundant, as make_number already does it. > > > > It can't, because json_int_t can be larger than EMACS_INT. > > OK, but then I think we should consider returning a float value, or a > cons of 2 integers. If these situations are frequent enough, users > will thank us, and if they are very infrequent, they will never see > such values, and we gain code simplicity and less non-local exits. > Returning a float (using make_natnum_or_float) might work, but in the end I've decided against it because it could silently drop precision. I think that's worse than signaling an error. > > > > > + case JSON_STRING: > > > > + { > > > > + size_t size = json_string_length (json); > > > > + if (FIXNUM_OVERFLOW_P (size)) > > > > + xsignal1 (Qoverflow_error, build_string ("JSON string is > too > > > long")); > > > > + return json_make_string (json_string_value (json), size); > > > > > > Once again, the overflow test is redundant, as make_specified_string > > > (called by json_make_string) already includes an equivalent test. > > > > And once again, we need to check at least whether the size fits into > > ptrdiff_t. > > No, we don't, as we don't in other similar cases. > I don't understand why you think these checks aren't necessary. Converting between integral types when the number is out of range for the destination type results in an implementation-defined result, i.e. it's unportable. Even assuming the GCC convention, performing such conversions results in dangerously incorrect values. > > > > > + case JSON_ARRAY: > > > > + { > > > > + if (++lisp_eval_depth > max_lisp_eval_depth) > > > > + xsignal0 (Qjson_object_too_deep); > > > > + size_t size = json_array_size (json); > > > > + if (FIXNUM_OVERFLOW_P (size)) > > > > + xsignal1 (Qoverflow_error, build_string ("JSON array is > too > > > long")); > > > > + Lisp_Object result = Fmake_vector (make_natnum (size), > > > Qunbound); > > > > > > Likewise here: Fmake_vector makes sure the size is not larger than > > > allowed. > > > > Same as above: It can't. > > It can and it does. > No, it can't. make_natnum takes a ptrdiff_t argument, and when passing a value that's out of range for ptrdiff_t, it will receive an incorrect, implementation-defined value. > > > > > + case JSON_OBJECT: > > > > + { > > > > + if (++lisp_eval_depth > max_lisp_eval_depth) > > > > + xsignal0 (Qjson_object_too_deep); > > > > + size_t size = json_object_size (json); > > > > + if (FIXNUM_OVERFLOW_P (size)) > > > > + xsignal1 (Qoverflow_error, > > > > + build_string ("JSON object has too many > elements")); > > > > + Lisp_Object result = CALLN (Fmake_hash_table, QCtest, > Qequal, > > > > + QCsize, make_natnum (size)); > > > > > > Likewise here: make_natnum does the equivalent test. > > > > It doesn't and can't. > > Yes, it does: > > INLINE Lisp_Object > make_natnum (EMACS_INT n) > { > eassert (0 <= n && n <= MOST_POSITIVE_FIXNUM); <<<<<<<<<<<<<<< > EMACS_INT int0 = Lisp_Int0; > We're not talking about the same thing. What if make_natnum is called with a value that doesn't fit in EMACS_INT? Also an assertion is incorrect here because the overflowing value comes from user data.