The last two commits were meant to work around a supposed bug in
mingw-w64's dbghelp.h, but closer inspection reminded me that we're
not using dbghelp.h at all; legacy mingw doesn't have it, so we had to
declare the structures we needed ourselves based on the MSDN
documentation. What that documentation doesn't mention is that
MINIDUMP_EXCEPTION_INFORMATION is subject to a special, packed layout,
which we must represent using the __packed__ attribute.
dbghelp.dll expects that MINIDUMP_EXCEPTION_INFORMATION has a packed
layout and will crash if it doesn't (at least on 64-bit systems), but
as of this writing mingw-w64's version is not declared to be so.
Hence this workaround.
All the tests are passing for openjdk-src builds, but the non-src
openjdk build is crashing and there's trouble loading time zone info
from the embedded java.home directory.
Previously, we assumed that the "context" parameter to
GetThreadContext was only an output parameter, but it actually uses at
the value of CONTEXT::ContextFlags on entry to decide what parts of
the structure to fill in. We were getting lucking most of the time,
because whatever garbage was on the stack at that location had the
necessary bits set. When we weren't so lucky, we got all zeros for
the register values which sometimes lead to a crash depending on the
state of the thread being examined.
We now create a unique thunk for each vtable position so as to avoid
relying on using the return address to determine what method is to be
compiled and invoked, since we will not have the correct return address
in the case of a tail call. This required refactoring how executable
memory is allocated in order to keep AOT compilation working. Also, we
must always use the same register to hold the class pointer when
compiling virtual calls, and ensure that the pointer stays there until
the call instruction is executed so we know where to find it in the
thunk.
We now support immortal objects, which the GC will scan for references
but not consider for collection. On x86_64, we allocate JIT code memory
via mmap, which lets us map memory into the bottom 2GB of the address
space, ensuring that 32-bit relative jumps and calls work.
