[lldb-test] Add a testing harness for the JIT's IRMemoryMap
This teaches lldb-test how to launch a process, set up an IRMemoryMap,
and issue memory allocations in the target process through the map. This
makes it possible to test IRMemoryMap in a targeted way.
This has uncovered two bugs so far. The first bug is that Malloc
performs an adjustment on the pointer returned from AllocateMemory (for
alignment purposes) which ultimately allows overlapping memory regions
to be created. The second bug is that after most of the address space on
the host side is exhausted, Malloc may return the same address multiple
times. These bugs (and hopefully more!) can be uncovered and tested for
with targeted lldb-test commands.
At an even higher level, the motivation for addressing these bugs is
that they can lead to strange user-visible failures (e.g, variables
assume the wrong value during expression evaluation, or the debugger
crashes). See my third comment on this swift-lldb PR for an example:
I hope lldb-test is the right place to add this testing harness. Setting
up a gtest-style unit test proved too cumbersome (you need to recreate
or mock way too much debugger state), as did writing end-to-end tests
(it's hard to write a test that actually hits a buggy path).
With lldb-test, it's easy to read/generate the test input and parse the
test output. I'll attach a simple "fuzz" tester which generates failing
test cases to the Phab review. Here's an example:
Command: malloc(size=1024, alignment=32) Malloc: address = 0xca000 Command: malloc(size=64, alignment=16) Malloc: address = 0xca400 Command: malloc(size=1024, alignment=16) Malloc: address = 0xca440 Command: malloc(size=16, alignment=8) Malloc: address = 0xca840 Command: malloc(size=2048, alignment=16) Malloc: address = 0xcb000 Command: malloc(size=64, alignment=32) Malloc: address = 0xca860 Command: malloc(size=1024, alignment=16) Malloc: address = 0xca890 Malloc error: overlapping allocation detected, previous allocation at [0xca860, 0xca8a0)
Differential Revision: https://reviews.llvm.org/D47508