[RFC] perf tool: load data variable symbols

[Lin Ming <ming.m.lin@intel.com>]

Hi, all

Currently, perf tool only load function symbols when parsing perf.data.

But it is also helpful if variable symbols can be loaded.

For example, Intel load latency monitoring facility records data linear
address of the load operation. It's useful if the data linear address is
resolved into symbol, just like functions.

enum map_type {
        MAP__FUNCTION = 0,
        MAP__VARIABLE,
};

We already have MAP__VARIABLE defined, although it's not used now.

For both kernel and userspace applications, we can load the variable
symbols from .data and .bss section.

What do you think?

Thanks,
Lin Ming