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Re: [PATCH] 69517 - [5/6 regression] SEGV on a VLA with excess initializer elements
- From: Jason Merrill <jason at redhat dot com>
- To: Martin Sebor <msebor at gmail dot com>, Gcc Patch List <gcc-patches at gcc dot gnu dot org>
- Date: Wed, 23 Mar 2016 14:15:31 -0400
- Subject: Re: [PATCH] 69517 - [5/6 regression] SEGV on a VLA with excess initializer elements
- Authentication-results: sourceware.org; auth=none
- References: <56DCDB80 dot 90208 at gmail dot com>
On 03/06/2016 08:38 PM, Martin Sebor wrote:
There are a few additional points to note about the patch:
1) It restores the std::bad_array_length exception from N3639,
even though the class isn't specified by the C++ standard.
At first I thought that introducing a different (private)
type would be more appropriate, but in the end couldn't come
up with a good argument for not keeping the same type. Using
the same type also allows programs that rely on the exception
and that were built with GCC 4.9 to be ported to GCC 6 without
change.
Makes sense.
2) It hardwires a rather arbitrarily restrictive limit of 64 KB
on the size of the biggest C++ VLA. (This could stand to be
improved and made more intelligent, and perhaps integrated
with stack checking via -fstack-limit, after the GCC 6
release.)
The bounds checking should share code with build_new_1.
3) By throwing an exception for erroneous VLAs the patch largely
defeats the VLA Sanitizer. The sanitizer is still useful in
C++ 98 mode where the N3639 VLA runtime checking is disabled,
and when exceptions are disabled via -fno-exceptions.
Disabling the VLA checking in C++ 98 mode doesn't seem like
a useful feature, but I didn't feel like reverting what was
a deliberate decision.
What deliberate decision? The old code checked for C++14 mode because
the feature was part of the C++14 working paper. What's the rationale
for C++11 as the cutoff?
Jason