Conversion to Dalvik failed - uninitialized variable somewhere

Question

I'm trying to link my Android app with a JAR that was compiled with Free Pascal. I'm getting the following build error:

[2012-09-14 16:08:38 - MyApp] Dx 
EXCEPTION FROM SIMULATION:
[2012-09-14 16:08:38 - MyApp] Dx local 0009: invalid

[2012-09-14 16:08:38 - Yarxi] Dx ...at bytecode offset 00015f2c
locals[0000]: Lcom/mypackage/$Core$$_fpc_nestedvars$70;
locals[0001]: I
locals[0002]: I
locals[0003]: I
locals[0004]: I
locals[0005]: I
locals[0006]: I
locals[0007]: I
locals[0008]: I
locals[0009]: <invalid>
locals[000a]: <invalid>
(..more locals... much more)
locals[06db]: <invalid>
stack[0003]: I
stack[0002]: I
stack[0001]: [I
stack[top0]: int{0x00000000 / 0}
...while working on block 5f23
...while working on method $MyMethod$944$FPR1:(Lcom/mypackage/$Core$$_fpc_nestedvars$70;)V
...while processing $MyMethod$944$FPR1 (Lcom/mypackage/$Core$$_fpc_nestedvars$70;)V
...while processing com/mypackage/Core.class

[2012-09-14 16:08:40 - MyApp] Dx 1 error; aborting
[2012-09-14 16:08:40 - MyApp] Conversion to Dalvik format failed with error 1

The error seems to be that at some point, the code tries to read local 0009, which is not initialized.

Now, Pascal does not enforce initialization of local variables. Chances are, initialization was omitted in the first place. I've retained the JVM assembly file that Free Pascal generated for me. Those are assembled with Jasmin into class files. The file is huge - I'm not pasting it here.

Can someone please help me trace back the point of error to the source? The error is at bytecode offset 00015f2c. Is there a way to translate that back into assembly file line number?

Answer 1

Resolved. 00015f2c (89900 decimal) is, indeed, a bytecode offset within a method. I did the following.

First, I called Jasmin directly, passing the generated .j file and the -g option (generate line numbers):

java -jar %JASM% -g Core.j

Free Pascal does not emit -g by itself. This gave me an alternative Core.class file with line numbers in it, line numbers being relative to the FPC-generated .j file. Then I used javap to disassemble the class back into another .j file:

"%JDKROOT%\javap" -l -c Core.class >Core_WithLines.j

But this new .j file contained line numbers and offsets of each individual command. I then searched for offset 89900 in the offending method (note: offsets, as generated by javap, wrap at 65536). Then I looked at the LineNumberTable below that method's body (both offsets and line numbers wrap), found the line number in the source Core.j file that corresponded to this offset. Looked back at Core.j, and there was a comment that contained the line number of the Pascal source.

There was, indeed, a function call that passed an uninitialized variable - but as a var parameter.

The issue is something of a Pascal/JVM borderline issue. The variable was uninitialized, but it was passed by ref into a function to be returned from the latter. The compiler should've abstracted that away somehow, IMHO, but FPC did not.