Lost during the romfs conversion.

We use a polling thread to collect characters and place them in a queue.

Polling only, no interrupt yet.

fo_read() and fo_write().

sys_read and sys_write used to malloc a 40-byte uio structure, and never
freed it. Fixed it by free()ing before returning from these functions.

object::unload_segments() had a typo - it called load_segment() instead
of unload_segment(). This obviously caused a memory leak.

Implemented a backtrace() function API-compatible with glibc's function with
the same name. I need it for the leak detector (to determine which allocations
come from the same call tree), but it can also be useful for other things, and
perhaps even used by some applications (I am guessing the JVM does not use it,
though).

My implementation uses the "_Unwind*" functions which are part of gcc's runtime
libgcc_s, so they are supposedly correctly synchronized with the way gcc actually
keeps track of the call hierarchy. If I understand correctly, these functions
use a cut-down version of libunwind which is included in libgcc_s. I also wrote
an implementation using libunwind directly (left in the code in #if 0), but
couldn't get it to compile because of library dependency hell.

Minor code simplification.

Avoids a zombie.

If we fail to match the file name, we need to release the buffer
before bailing out.

We drop the buffer and fetch a new one, but we forget
to return the new one to the caller for an eventual
brelse().  This results in an assertion failure later on.

Fix by making sure the caller sees the new buffer.

This allows running either testrunner.so, or one of the tests (e.g.
test/tst-fpu.so), as they now both export the same entry point.

Used when names in an object may conflict with names in other objects.

Python has no pointers, so it doesn't support %p.  Convert it to %016x.

Use:

  debug("foo %s %x\n", foo.x, foo.y);

Instead of:

  debug(boost::format("foo %s %x\n") % foo.x % foo.y);

note this uses boost::format, not *printf(), so size modifers ("%lx") are
unneeded.

This is only causing confusion; change all callers to add '\n' explicitly
and drop the optional argument.

Variable size trace records.

To conserve space, we now use variable size trace records.  To avoid problems
with wrap-arounds, and with recovering a complete entry at the head of the
ring buffer, we don't allow a trace record to cross a 4096-byte boundary.

When out of memory in alloc_page() or malloc_large(), we used to produce
mysterious assertion failures or aborts. Now print a more user-friendly
"out of memory" error (and abort).

To run the debug build, instead of "scripts/run.sh debug", use
"scripts/run -d".

With a ring buffer, we need to know the size before writing to determine
if we wrap around.

Also fix the numbering.

On a 32-bit system, a 64-bit value need only be aligned to 32 bits, not 64.
Change the code to reflect that.

Tracepoint command line support.

Enable via command line.

usage: --trace=a,b,c,*foo* --trace=bar java.so ...

Will match on tracepoint names.

e.g.

  enable_tracepoint("*function*");

We used to have libz in bootfs.manifest, and now that it was removed, it
needs to be put in usr.manifest... It is needed by Java to load the
compressed jar.

"osv info threads" used to show the switch_to() function for all non-running
threads. Now, it attempts to skip "obvious" functions until finding a less
obvious caller which initiated the final thread switch.

Currently, the mechanism to define obvious functions is pretty crude - it
just considers all functions in arch-switch.hh, sched.cc, sched.hh or
mutex.hh, to be obvious, avoiding showing things like switch_to(),
schedule(), wait_until(). In the future we can refine this definition.
In my opinion it would be best if we could decide on one file (or a small
set of files) which contain all these generic switching/waiting functions
and we'll simply avoid showing anything from these files in "osv info threads".

Since commit 5384840a which changed the way we remember a
non-running thread's rip and rbp, "osv info threads" was broken and
showed question marks for all non-running threads. Now it's fixed
but always shows sched::thread::switch_to() as non-running threads
indeed called this function last.