965762 - ARM Simulator: support an environment variable and shell argument to drop into the debugger after a given number of instructions

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, defect)

Description

[Douglas Crosher [:dougc]]

A convenient way to drop into the debugger helps debugging.  Breaking after a given number of instructions is also useful when debugging.

This patch adds the shell argument --arm-sim-stop-at and the environment variable ARM_SIM_STOP_AT.

Comment 1

[Douglas Crosher [:dougc]]

Attachment: Support an environment variable and shell argument to drop into the debugger after a given number of instructions

Comment 2

[Jan de Mooij [:jandem]]

Comment on attachment 8367883 [details] [diff] [review]
Support an environment variable and shell argument to drop into the debugger after a given number of instructions

Review of attachment 8367883 [details] [diff] [review]:
-----------------------------------------------------------------

::: js/src/jit/arm/Simulator-arm.cpp
@@ +4013,5 @@
>          }
> +    } else {
> +        while (program_counter != end_sim_pc) {
> +            SimInstruction *instr = reinterpret_cast<SimInstruction *>(program_counter);
> +            if (icount_ == Simulator::StopSimAt) {

This looks good but I think we could avoid the duplication without hurting performance in the common no-limit case if we templatized execute, something like this:

template <bool HasInstructionLimit>
void
Simulator::execute()
{
    ...
    if (HasInstructionLimit && icount_ == Simulator::StopSimAt) {
        ...
    }
}

This way the compiler generates two copies of execute and will optimize the extra check away if HasInstructionLimit is false. The caller can check Simulator::StopSimAt and call execute with either HasInstructionLimit true or false.

What do you think?

Comment 3

[Douglas Crosher [:dougc]]

Attachment: Support an environment variable and shell argument to drop into the debugger after a given number of instructions

Rework to use a template.  Also account for instruction counts in the debugger.

Comment 4

[Douglas Crosher [:dougc]]

Note this patch assumes that the patch in bug 966570 has been applied.  Both are ready to checkin.

Comment 5

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/52f8f3e943d6

Comment 6

[Phil Ringnalda (:philor)]

https://hg.mozilla.org/mozilla-central/rev/52f8f3e943d6