Re: [PATCH 2/5] tracing: Add division and multiplication support for hist triggers

On Tue, Oct 19, 2021 at 1:45 PM Steven Rostedt rostedt@goodmis.org wrote:

On Wed, 15 Sep 2021 19:52:46 +0000 Kalesh Singh kaleshsingh@google.com wrote:

...

+static u64 hist_field_div(struct hist_field *hist_field,

•                    struct tracing_map_elt *elt,
  

•                    struct trace_buffer *buffer,
  

•                    struct ring_buffer_event *rbe,
  

•                    void *event)
  

+{

• struct hist_field *operand1 = hist_field->operands[0];
  

• struct hist_field *operand2 = hist_field->operands[1];
  

• u64 val1 = operand1->fn(operand1, elt, buffer, rbe, event);
  

• u64 val2 = operand2->fn(operand2, elt, buffer, rbe, event);
  

• /* Return -1 for the undefined case */
  

• if (!val2)
  

•         return -1;
  

• return val1 / val2;
  

This wont work on x86 32 bit machines, as u64 division will trigger floating point arithmetic by the compiler, and cause a fault.

Thanks for catching this. I'll address it in the next version.

- Kalesh

You'll need to use one of the div64() helpers.

-- Steve

...

+}