Re: [Qemu-devel] ARM NEON function call tracing

["Alex Bennée" <alex.bennee@linaro.org>]

Peter Maydell <peter.maydell@linaro.org> writes:

> On 11 November 2015 at 07:51, Junaid Shuja <junaidshuja@siswa.um.edu.my> wrote:
>> Hi,
>> I am working on ARM/NEON instructions. I want to know which neon helper
>> function corresponds to the neon instructions. As a test case, I have a
>> source file with loads of vadd.i32 instructions. I want to trace which neon
>> helper functions is called. I used a very crude approach: printf in
>> neon_add_u16 funtion and compiled source again. But no printf showed on
>> program execution. I need help regarding tracing of neon helpers.
>
> Integer addition is a simple operation so we can do it directly
> in the generated code; we don't need a helper for it, even as a
> Neon instruction. Generally we only have helper functions for
> operations that are too complicated to do directly inline.
> So there isn't a simple "one neon instruction, one helper function"
> mapping. Where we do have a helper function, the helper
> may work on one "lane" of Neon data (meaning it gets called
> more than once for each instruction) or it may work on several
> lanes at once.
>
> To find out how we handle a particular Neon instruction, you need
> to look at disas_neon_data_insn and see what it does with the
> insn (it may be easiest to do this by putting a breakpoint on
> it and stepping through with a debugger). Where this code calls
> gen_helper_* functions, it is emitting generated code which will
> later call the relevant helper at runtime.

Random musing: I wonder how easy it would be to emit the helper function
name in the out_asm dump?

>
> thanks
> -- PMM


-- 
Alex Bennée