With this only `ContinuePendingUnwind` needs to dynamically check if a
scheduled return needs to go through a `finally` block, making the
interpreter loop a bit nicer
This actually allows us to re-introduce the ldd utility as a symlink to
our dynamic loader, so now ldd behaves exactly like on Linux - it will
load all dynamic dependencies for an ELF exectuable.
This has the advantage that running ldd on an ELF executable will
provide an exact preview of how the order in which the dynamic loader
loads the executable and its dependencies.
As a preparation to introducing ldd as a symlink to /usr/lib/Loader.so
we rename the ldd utility to be elfdeps, at its sole purpose is to list
ELF object dependencies, and not how the dynamic loader loads them.
This is useful for testing ELF binaries that expose other functionalites
based on the argv0 string (BuggieBox, for example, does it to determine
which utility to run).
This change essentially puts the DynamicLoader with 2 roles - the first
one is to be invoked by the kernel to dynamically link an ELF executable
in runtime.
The second role is to allow running ELF executables explicitly from
userspace so the kernel runs the DynamicLoader as the "intended" program
but now the DynamicLoader can do its own commandline argument parsing
and run a specified binary, with future options being possible to
implement easily.
This will be used in the DynamicLoader code, as it can't do syscalls via
LibCore code.
Because we can't use most of the LibCore code, we convert the versioning
code in Version.cpp to use LibC uname() function.
Instead of SetVariable having 2x2 modes for variable/lexical and
initialize/set, those 4 modes are now separate instructions, which
makes each instruction much less branchy.
The last completion value in a function is not exposed to the language,
since functions always either return something, or undefined.
Given this, we can avoid emitting code that propagates the completion
value from various statements, as long as we know we're generating code
for a context where the completion value is not accessible. In practical
terms, this means that function code gets to do less completion
shuffling, while global and eval code has to keep doing it.
We add a prctl option which would be called once after the dynamic
loader has finished to do text relocations before calling the actual
program entry point.
This change makes it much more obvious when we are allowed to change
a region protection access from being writable to executable.
The dynamic loader should be able to do this, but after a certain point
it is obvious that such mechanism should be disabled.
This flag is set only once, and should never reset once it has been set,
making it an ideal SetOnce use-case.
It also simplifies the expected conditions for the enabling prctl call,
as we don't expect a boolean flag, but rather the specific prctl option
will always set (enable) Process' AddressSpace syscall region enforcing.
Now both /bin/zcat and /bin/gunzip are symlinks to /bin/gzip, and we
essentially running it in decompression mode through these symlinks.
This ensures we don't maintain 2 versions of code to decompress Gzipped
data anymore, and handle the use case of gzipped-streaming input only
once in the codebase.
For example, for 7z7c.gif, we now store one 500x500 frame and then
a 94x78 frame at (196, 208) and a 91x78 frame at (198, 208).
This reduces how much data we have to store.
We currently store all pixels in the rect with changed pixels.
We could in the future store pixels that are equal in that rect
as transparent pixels. When inputs are gif files, this would
guaranteee that new frames only have at most 256 distinct colors
(since GIFs require that), which would help a future color indexing
transform. For now, we don't do that though.
The API I'm adding here is a bit ugly:
* WebPs can only store x/y offsets that are a multiple of 2. This
currently leaks into the AnimationWriter base class.
(Since we potentially have to make a webp frame 1 pixel wider
and higher due to this, it's possible to have a frame that has
<= 256 colors in a gif input but > 256 colors in the webp,
if we do the technique above.)
* Every client writing animations has to have logic to track
previous frames, decide which of the two functions to call, etc.
This also adds an opt-out flag to `animation`, because:
1. Some clients apparently assume the size of the last VP8L
chunk is the size of the image
(see https://github.com/discord/lilliput/issues/159).
2. Having incremental frames is good for filesize and for
playing the animation start-to-end, but it makes it hard
to extract arbitrary frames (have to extract all frames
from start to target frame) -- but this is mean tto be a
delivery codec, not an editing codec. It's also more vulnerable to
corrupted bytes in the middle of the file -- but transport
protocols are good these days.
(It'd also be an idea to write a full frame every N frames.)
For https://giphy.com/gifs/XT9HMdwmpHqqOu1f1a (an 184K gif),
output webp size goes from 21M to 11M.
For 7z7c.gif (an 11K gif), output webp size goes from 2.1M to 775K.
(The webp image data still isn't compressed at all.)
This means that SetVariable instructions will now remember which
(relative) environment contains the targeted binding, letting it bypass
the full binding resolution machinery on subsequent accesses.