bytecode | lightweight Java bytecode parsing and manipulation library | Bytecode library
kandi X-RAY | bytecode Summary
kandi X-RAY | bytecode Summary
Fast, lightweight Java bytecode manipulation library.
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Top functions reviewed by kandi - BETA
- Calls the visitor .
- Reads a 64 - bit long from the stream .
- Visit a description .
- Write exceptions .
- write method descriptor .
- Print an info message .
- Creates a byte array from the input stream .
- Method handle .
- Visit a single stack item extended?
- Returns a pattern that can be used as an identifier .
bytecode Key Features
bytecode Examples and Code Snippets
Community Discussions
Trending Discussions on bytecode
QUESTION
I'm trying to extract method parameters information from Java class bytecode using asm MethodVisitor
. visitParameter
method of MethodVisitor
is not called (because no parameter names are present in compiled class file). How can i get count of method parameters and their types?
The only thing I've found so far is desc
parameter of visitMethod
from MethodVisitor
. I can copy-paste TraceSignatureVisitor
class from asm-util, rewrite about 50 lines of code to store parameters declarations into List/array instead of single StringBuffer
.
Another option is suggested by in answer "https://stackoverflow.com/questions/18061588/get-function-arguments-values-using-java-asm-for-bytecode-instrimentation":
The number of arguments to the method can be computed from the method description using the code in the following gist: https://gist.github.com/VijayKrishna/6160036. Using the
parseMethodArguments(String desc)
method you can easily compute the number of arguments to the method.
From my point of view copy-pasting and rewriting TraceSignatureVisitor
is still better.
But i suppose there should be more simple way to work with method signatures in asm-util. Is there?
...ANSWER
Answered 2021-Jun-14 at 07:55ASM has an abstract for that purpose, Type
.
Instances of Type
may represent a primitive type, a reference type, or a method type. So you can first get a type to represent the method type from the descriptor string, followed by querying it for the parameter types and return type.
QUESTION
I am currently learning DirectX 12 and trying to get a demo application running. I am currently stuck at creating a pipeline state object using a root signature. I am using dxc to compile my vertex shader:
...ANSWER
Answered 2021-Jun-14 at 06:33Long story short: shader visibility in DX12 is not a bit field, like in Vulkan, so setting the visibility to D3D12_SHADER_VISIBILITY_VERTEX | D3D12_SHADER_VISIBILITY_PIXEL
results in the parameter only being visible to the pixel shader. Setting it to D3D12_SHADER_VISIBILITY_ALL
solved my problem.
QUESTION
I am trying to learn how ELF files are structured and probably how to make one manually.
I am working on aarch64 Linux OS, the ELF files I am inspecting are of elf64-littleaarch64
format.
Also I try to learn by myself, however I got stuck with some questions...
- When I do
xxd code
, the first number in each line of the output specifies the address of bytes in the file. But whenobjdump -D code
, the first number is something like4000b0
, however corresponds to000000b0
inxxd
. Why is there a four at the beginning? - In
objdump
, the bytecode is for example11000a94
, which 'means'add w20, w20, #2
in assembly. I know, that11
is the opcode, but what does000a94
mean? I thought, it should be the parameters, but I am adding the value 2 and can't find the number 2 in it.
If you have a good article to read, or can help me explain this, I will be very grateful!
...ANSWER
Answered 2021-Jun-09 at 11:15Well, I was too fast asking this question, but now, I will answer it too.
40
at the beginning of the addresses inobjdump
is the hex representation of the char "@", which means "at" and points to an address, very simple!- Little Endian has CPU addresses stored in 5 bits instead of 6 or 8. That means, that I should look for the binary value of the
objdump
code:11000a94
-->10001000000000000101010010100
, where it can be divided into[10001][00000000000010][10100][10100]
with[opcode][value][first address][second address]
Both answers are wrong, see the accepted answer. I will still let them here, though
QUESTION
I am trying to implement react-native-maps in my App (react native version 64.1)
This is the source I'm using to integrate maps to my app
when I try to sync my project using Android Studio I get these errors (screenshot):
...ANSWER
Answered 2021-May-23 at 12:06Before running the run-android
run command, navigate to the android directory and enter ./gradlew clean
command. After that enter the run-android
command again.
QUESTION
I am trying to lunch my flutter application on my mobile but When I run
...ANSWER
Answered 2021-Jun-05 at 13:35you flutter channel is unknown .
the version is unknown and seems to be on web developer mode so
if you are using it for android devices , it is better to switch to
QUESTION
I am going to write my own FORTH "engine" in GNU assembler (GAS) for Linux x86-64 (specifically for AMD Ryzen 9 3900X that is siting on my table).
(If it will be success, I may use similar idea for make firmware for retro 6502 and similar home-brewed computer)
I want to add some interesting debugging features, as saving comments with the compiled code in for of "NOP words" with attached strings, which would do nothing in runtime, but when disassembling/printing out already defined words it would print those comment too, so it would not loose all the headers ( a b -- c) and comments like ( here goes this particular little trick ) and I would be able try to define new words with documentation, and later print all definitions in some nice way and make new library from those, which I consider good. (And have switch to just ignore comments for "production release")
I had read too much of optimalization here and I am not able to understand all of that in few weeks, so I will put out microoptimalisation until it will suffer performance problems and then I will start with profiling.
But I want to start with at least decent architectural decisions.
What I understood yet:
- it would be nice, if the programs was run mainly from CPU cache, not from memory
- the cache is filled somehow "automagically", but having related data/code compact and as near as possible may help a lot
- I identified some areas, that would be good candidates for caching and some, that are not so good - I sorted it in order of importance:
- assembler code - the engine and basic words like "+" - used all the time (fixed size, .text section)
- both stacks - also used all the time (dynamic, I will probably use rsp for data stack and implement return stack independly - not sure yet, which will be "native" and which "emulated")
- forth bytecode - the defined and compiled words - used at runtime, when the speed matters (still growing size)
- variables, constants, strings, other memory allocations (used in runtime)
- names of words ("DUP", "DROP" - used only when defining new words in compilation phase)
- comments (used one daily or so)
As there is lot of "heaps" that grows up (well, there is not "free" used, so it may be also stack, or stack growing up) (and two stacks that grows down) I am unsure how to implement it, so the CPU cache will cover it somehow decently.
My idea is to use one "big heap" (and increse it with brk() when needed), and then allocate big chunks of alligned memory on it, implementing "smaller heaps" in each chunk and extend them to another big chunk when the old one is filled up.
I hope, that the cache would automagically get the most used blocks first keep it most of the time and the less used blocks would be mostly ignored by the cache (respective it would occupy only small parts and get read and kicked out all the time), but maybe I did not it correctly.
But maybe is there some better strategy for that?
...ANSWER
Answered 2021-Jun-04 at 23:53Your first stops for further reading should probably be:
- What Every Programmer Should Know About Memory? re: cache
- https://agner.org/optimize/ re: everything else about writing efficient asm.
- https://uops.info/ for a better version of Agner Fog's instruction tables.
- See also other links in https://stackoverflow.com/tags/x86/info
so I will put out microoptimalisation until it will suffer performance problems and then I will start with profiling.
Yes, probably good to start trying stuff so you have something to profile with HW performance counters, so you can correlate what you're reading about performance stuff with what actually happens. And so you get some ideas of possible details you hadn't thought of yet before you go too far into optimizing your overall design idea. You can learn a lot about asm micro-optimization by starting with something very small scale, like a single loop somewhere without any complicated branching.
Since modern CPUs use split L1i and L1d caches and first-level TLBs, it's not a good idea to place code and data next to each other. (Especially not read-write data; self-modifying code is handled by flushing the whole pipeline on any store too near any code that's in-flight anywhere in the pipeline.)
Related: Why do Compilers put data inside .text(code) section of the PE and ELF files and how does the CPU distinguish between data and code? - they don't, only obfuscated x86 programs do that. (ARM code does sometimes mix code/data because PC-relative loads have limited range on ARM.)
Yes, making sure all your data allocations are nearby should be good for TLB locality. Hardware normally uses a pseudo-LRU allocation/eviction algorithm which generally does a good job at keeping hot data in cache, and it's generally not worth trying to manually clflushopt
anything to help it. Software prefetch is also rarely useful, especially in linear traversal of arrays. It can sometimes be worth it if you know where you'll want to access quite a few instructions later, but the CPU couldn't predict that easily.
AMD's L3 cache may use adaptive replacement like Intel does, to try to keep more lines that get reused, not letting them get evicted as easily by lines that tend not to get reused. But Zen2's 512kiB L2 is relatively big by Forth standards; you probably won't have a significant amount of L2 cache misses. (And out-of-order exec can do a lot to hide L1 miss / L2 hit. And even hide some of the latency of an L3 hit.) Contemporary Intel CPUs typically use 256k L2 caches; if you're cache-blocking for generic modern x86, 128kiB is a good choice of block size to assume you can write and then loop over again while getting L2 hits.
The L1i and L1d caches (32k each), and even uop cache (up to 4096 uops, about 1 or 2 per instruction), on a modern x86 like Zen2 (https://en.wikichip.org/wiki/amd/microarchitectures/zen_2#Architecture) or Skylake, are pretty large compared to a Forth implementation; probably everything will hit in L1 cache most of the time, and certainly L2. Yes, code locality is generally good, but with more L2 cache than the whole memory of a typical 6502, you really don't have much to worry about :P
Of more concern for an interpreter is branch prediction, but fortunately Zen2 (and Intel since Haswell) have TAGE predictors that do well at learning patterns of indirect branches even with one "grand central dispatch" branch: Branch Prediction and the Performance of Interpreters - Don’t Trust Folklore
QUESTION
I am using groovy 2.4.12 with Oracle JVM 1.8. I am trying to understand a bit how groovyc
converts the scripts written by end users.
To that end I wrote this simple script:
...ANSWER
Answered 2021-Jun-03 at 17:45use another decompiler to see it
QUESTION
I'm working on a search that I can use with flutter_typeahed package.
I found a package called trie
, but it doesn't have null safety so I thought of including that and contribute to the project as well as my own.
Since the entire trie
file is quite big, I'm providing a link to pastebin.
This is the Search
class that I've written:
ANSWER
Answered 2021-Jun-03 at 17:25I had to enable multidex. And I had to change the following things:
QUESTION
I am creating a Smart Contract (BEP20 token) based on the BEP20Token template (https://github.com/binance-chain/bsc-genesis-contract/blob/master/contracts/bep20_template/BEP20Token.template). The public contructor was modified to add some token details. However all of the standard functions are giving compile time issues like Overriding function is missing.
** here is the source code **
...ANSWER
Answered 2021-May-11 at 13:28Constructor public () - Warning: Visibility for constructor is ignored. If you want the contract to be non-deployable, making it "abstract" is sufficient.
The warning message says it all. You can safely remove the public
visibility modifier because it's ignored anyway.
If you marked the BEP20Token
contract abstract, you would need to have a child contract inheriting from it, could not deploy the BEP20Token
itself, but would have to deploy the child contract. Which is not what you want in this case.
QUESTION
I am new to programming, working on a project to explore bytecode for Python. I have several python files with .py extensions and would like to use the dis.dis()
function to save the bytecode equivalent of a lot of small programs.
For example, the code below, when run, will return the bytecode of the function (what's in the def
part). My problem is that I cannot find a solution to import the files as text/code, for all the functions they define, and run this code over thousands of examples.
ANSWER
Answered 2021-May-31 at 13:56I have managed to find a solution with the help of my supervisor. This doesn't account for special circumstances, such as a space in the filename, but does solve the problem by saving the bytecode in .txt
files:
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Install bytecode
You can use bytecode like any standard Java library. Please include the the jar files in your classpath. You can also use any IDE and you can run and debug the bytecode component as you would do with any other Java program. Best practice is to use a build tool that supports dependency management such as Maven or Gradle. For Maven installation, please refer maven.apache.org. For Gradle installation, please refer gradle.org .
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