We should define EXPORT to be __declspec(dllexport) on Windows
regardless of architecture, not just non-x86_64 arches. This fixes
errors to to embedded JAVA_HOME files not being found in openjdk-src
builds, e.g. lib/currency.data.
Previously, I used a shell script to extract modification date ranges
from the Git history, but that was complicated and unreliable, so now
every file just gets the same year range in its copyright header. If
someone needs to know when a specific file was modified and by whom,
they can look at the Git history themselves; no need to include it
redundantly in the header.
This avoids the requirement of putting the code image in a
section/segment which is both writable and executable, which is good
for security and avoids trouble with systems like iOS which disallow
such things.
The implementation relies on relative addressing such that the offset
of the desired address is fixed as a compile-time constant relative to
the start of the memory area of interest (e.g. the code image, heap
image, or thunk table). At runtime, the base pointer to the memory
area is retrieved from the thread structure and added to the offset to
compute the final address. Using the thread pointer allows us to
generate read-only, position-independent code while avoiding the use
of IP-relative addressing, which is not available on all
architectures.
GCC 4.5.1 and later use a naming convention where functions are not
prefixed with an underscore, whereas previous versions added the
underscore. This change was made to ensure compatibility with
Microsoft's compiler. Since GCC 4.5.0 has a serious code generation
bug, we now only support later versions, so it makes sense to assume
the newer convention.
This allows OpenJDK to access time zone data which is normally found
under java.home, but which we must embed in the executable itself to
create a self-contained build. The VM intercepts various file
operations, looking for paths which start with a prefix specified by
the avian.embed.prefix property and redirecting those operations to an
embedded JAR.
For example, if avian.embed.prefix is "/avian-embedded", and code
calls File.exists() with a path of
"/avian-embedded/javahomeJar/foo.txt", the VM looks for a function
named javahomeJar via dlsym, calls the function to find the memory
region containing the embeded JAR, and finally consults the JAR to see
if the file "foo.txt" exists.
The trick is to make all destructors non-virtual. This is safe because
we never use the delete operator, which is the only case where virtual
destructors are relevant. This is a better solution than implementing
our own delete operator, because we want libraries loaded at runtime to
use the libstdc++ version, not ours.
