ldc2 --checkaction=halt produces same binary as --checkaction=D

[denizzzka]

(I want to halt if assertion occured.)

Tried on x86_64 and ARM32

Code for check:

void main()
{
    assert(false, "Please, HLT me!");
}

[kinke]

Thx for the report. Looks like there's no DMD test for this...

[denizzzka]

@kinke Looks like for ARM 8813f0e emits "undefined" TRAP instruction (0xDEFE) from LLVM's __builtin_trap.

This instruction causes immediate jump to blocking_handler vector value what typically contains infinity loop.

But -checkaction=halt described as "Halt the program execution (very lightweight)".
Also this jump leads to lose stack trace. Not exactly what is need for debug (To jump into blocking_handler it is possible to use more highlevel ways (abort() call, for example.)

Looks like ARM isn't have appropriate "Halt and Catch Fire" instruction?

[kinke]

The fix uses the llvm.trap intrinsic, just like an assert(0) with -release. For x86, that's ud2. See http://llvm.org/docs/LangRef.html#llvm-trap-intrinsic for the official description. Right below that one, there's llvm.debugtrap.

[denizzzka]

debugtrap looks as more appropriate at least for ARM - it adds BKPT instruction instead of undefined "TRAP".

From ARM manual:
The BKPT instruction causes the processor to enter Debug state. Debug tools can use this to investigate system state when the instruction at a particular address is reached.

While in debug state, the processor behaves as follows:

• The DBGDSCR[0] core halted bit is set.
• The DBGACK signal is asserted, see DBGACK.
• The DBGDSCR[5:2] method of entry bits are set appropriately.
• The processor is halted. The pipeline is flushed and no instructions are fetched.
• The processor does not change the execution mode. The CPSR is not altered.
• Exceptions are treated as described in Exceptions in debug state.
• Interrupts are ignored.
• New debug events are ignored.

[kinke]

Then please play around with it and see if it fits your needs. If it does, open a PR to discuss whether this should be the default, only used with -g or for ARM etc.

Edit: I've only found http://llvm.1065342.n5.nabble.com/Trap-instruction-for-ARMv7-and-Thumb-td59521.html wrt. this.

[denizzzka]

I’m afraid to touch ldc sources and don’t know how to test different platforms. I will just create a Issue ticket.

[kinke]

You can trivially substitute trap by debugtrap in

ldc/gen/toir.cpp

Line 1688 in 9a92488

p->ir->CreateCall(GET_INTRINSIC_DECL(trap), {});

(even with the GitHub editor) and then open a draft PR. CI will take care of building and testing everything; you can then download a prebuilt artifact from Azure Pipelines and test it with your code.

Yes, it's really that simple.

[denizzzka]

Azure Pipelines

I am on linux

[kinke]

So what? Azure builds all packages.

[denizzzka]

Ok, will try it