bcraig added a comment.
So I definitely see a problem, and I think your fix is a reasonable solution to
that problem. I'm still unclear on how that caused the ASAN error though.
Here's my understanding of the current problem...
The initial buffer for strstreambuf is often 4096 ( _strstream> line 184,
__default_alsize = 4096;).
So we have a 4096 character string, and push that into strstreambuf. There
shouldn't be any calls to overflow because of that.
Now, we push in an ends(). This causes a call to overflow(). overflow()
allocates a new buffer of twice the size, then saves off the relevant put and
get range sizes for the old buffer. The old capacity ranges (einp and eout)
should add up to 4096. We then set the new range sizes using the old range
sizes. THIS SEEMS WRONG. We have an 8K buffer, but we are only setting it
with 4K sizes. We then write ends() into the no-mans-land past the end of
epptr() (well, exactly at epptr), and then advance pptr() past epptr().
I can see this causing a lot of trouble, as some code compares pptr() ==
epptr(), and we've broken that.
However, I would expect ASAN to require an extra call to overflow() before
things explode. strlen should still find that end() that we placed. Maybe
there's an extra overflow() that I didn't see though.
I would like to see a new test added to exercise this use case. The test
should probably live somewhere under
test/std/depr/depr.str.strstreams/depr.strstreambuf. Your example code is
going to be pretty close to what you would want to put there (maybe a
string.resize instead of the stringOfLength() function you have). I believe
you can run the tests using address sanitizer by setting
LLVM_USE_SANITIZER="Address" to your cmake line. "make check-libcxx" will then
compile the tests (and libcxx?) with ASAN.
================
Comment at: src/strstream.cpp:174
@@ -173,3 +173,3 @@
ptrdiff_t nout = pptr() - pbase();
ptrdiff_t eout = epptr() - pbase();
if (__strmode_ & __allocated)
----------------
This is now unused.
http://reviews.llvm.org/D20334
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