jasm reporting [BUG]: <Unknown> [java.lang.NullPointerException

[alexgarzao]

Hello! I'm using jasm in a "toy compiler". It's an amazing project :-)

I assembled a lot of jasm files, without any problem. But, with the example bellow, I got a "[BUG]: [java.lang.NullPointerException".

I'm using jasm 0.7.0, installed from the binary distribution.

public class if_with_integers_with_and_or {
	public static main([java/lang/String)V {
		sipush 2
		sipush 1
		if_icmple L3
		iconst_1 
		goto L4
		L3:
		iconst_0 
		L4:
		ifeq L1
		getstatic java/lang/System.out java/io/PrintStream
		ldc "true"
		invokevirtual java/io/PrintStream.print(java/lang/String)V
		getstatic java/lang/System.out java/io/PrintStream
		invokevirtual java/io/PrintStream.println()V
		goto L2
		L1:
		getstatic java/lang/System.out java/io/PrintStream
		ldc "false"
		invokevirtual java/io/PrintStream.print(java/lang/String)V
		getstatic java/lang/System.out java/io/PrintStream
		invokevirtual java/io/PrintStream.println()V
		L2:
		return
	}
}

Could someone help me?

Regards.

[cdluv]

Might help if youre able to share the java source that got compiled to this? At least for context....

…

On Sat, 30 Mar 2024, 02:30 Alex Sandro Garzão, ***@***.***> wrote: Hello! I'm using jasm in a "toy compiler". It's an amazing project :-) I assembled a lot of jasm files, without any problem. But, with the example bellow, I got a "[BUG]: [java.lang.NullPointerException". I'm using jasm 0.7.0, installed from the binary distribution. public class if_with_integers_with_and_or { public static main([java/lang/String)V { sipush 2 sipush 1 if_icmple L3 iconst_1 goto L4 L3: iconst_0 L4: ifeq L1 getstatic java/lang/System.out java/io/PrintStream ldc "true" invokevirtual java/io/PrintStream.print(java/lang/String)V getstatic java/lang/System.out java/io/PrintStream invokevirtual java/io/PrintStream.println()V goto L2 L1: getstatic java/lang/System.out java/io/PrintStream ldc "false" invokevirtual java/io/PrintStream.print(java/lang/String)V getstatic java/lang/System.out java/io/PrintStream invokevirtual java/io/PrintStream.println()V L2: return } } Could someone help me? Regards. — Reply to this email directly, view it on GitHub <#56>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA534DQZNHQTR4T6R4FSU2TY2YPUTAVCNFSM6AAAAABFPFWDJ6VHI2DSMVQWIX3LMV43ASLTON2WKOZSGIYTMMJWGA4DKNY> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[alexgarzao]

My project is a compiler that translates a subset of the Pascal language to Java assembly. After that I am using jasm to create the final class file. Just like jasm, I'm using ANTLR but with the Go runtime. The project is at https://github.com/alexgarzao/poj, but all the docs are in pt-br :-| Em sex., 29 de mar. de 2024, 23:37, Gary Fry ***@***.***> escreveu:

…

Might help if youre able to share the java source that got compiled to this? At least for context.... On Sat, 30 Mar 2024, 02:30 Alex Sandro Garzão, ***@***.***> wrote: > Hello! I'm using jasm in a "toy compiler". It's an amazing project :-) > > I assembled a lot of jasm files, without any problem. But, with the > example bellow, I got a "[BUG]: [java.lang.NullPointerException". > > I'm using jasm 0.7.0, installed from the binary distribution. > > public class if_with_integers_with_and_or { > public static main([java/lang/String)V { > sipush 2 > sipush 1 > if_icmple L3 > iconst_1 > goto L4 > L3: > iconst_0 > L4: > ifeq L1 > getstatic java/lang/System.out java/io/PrintStream > ldc "true" > invokevirtual java/io/PrintStream.print(java/lang/String)V > getstatic java/lang/System.out java/io/PrintStream > invokevirtual java/io/PrintStream.println()V > goto L2 > L1: > getstatic java/lang/System.out java/io/PrintStream > ldc "false" > invokevirtual java/io/PrintStream.print(java/lang/String)V > getstatic java/lang/System.out java/io/PrintStream > invokevirtual java/io/PrintStream.println()V > L2: > return > } > } > > Could someone help me? > > Regards. > > — > Reply to this email directly, view it on GitHub > <#56>, or unsubscribe > < https://github.com/notifications/unsubscribe-auth/AA534DQZNHQTR4T6R4FSU2TY2YPUTAVCNFSM6AAAAABFPFWDJ6VHI2DSMVQWIX3LMV43ASLTON2WKOZSGIYTMMJWGA4DKNY> > . > You are receiving this because you are subscribed to this thread.Message > ID: ***@***.***> > — Reply to this email directly, view it on GitHub <#56 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABJ5V4FP6RTMJ3LNEVHSLPLY2YQNBAVCNFSM6AAAAABFPFWDJ6VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDAMRXHA4DKOBSG4> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[roscopeco]

Hello! Glad to hear you're finding it useful, and thank you for the kind comments :)

The issue you're having is caused by the iconst lines - the correct syntax for iconst is:

iconst <num>

i.e. there are not separate instructions for the individual constants. If you remove the underscore, e.g.

iconst_1     => iconst 1
iconst_0     => iconst 0

Then it should work 🙂

So that's a workaround, however I do consider this to be a bug - it should be giving useful error messaging rather than a NullPointerException so will look at getting that fixed - thanks for the report!

[alexgarzao]

Using "iconst 0" and "iconst 1" works fine. Thanks :-)

Just a small question about the project. Is JASM intended to implement all JVM opcodes? In that case, I suggest taking a look at [Oracle documentation](https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-6.html#:~:text=an% 20ArrayIndexOutOfBoundsException.- ,iconst_%3Ci%3E,-Operation). In this document, if I'm not mistaken, there are opcodes iconst_0 and iconst_1.

[roscopeco]

great, glad to hear the workaround fixed it for you 🥳

Indeed, those are the opcodes, and under the hood jasm assembles the code to the appropriate one based on the number - as an assembler, the syntax is designed to be consistent and convenient rather than necessarily exactly matching the underlying bytecode 🙂.

[alexgarzao]

Nice. I got it. Thanks for your help!