Re: [Libunwind-devel] Explicitly exporting CFA

[Andrew Cagney]

Arun Sharma wrote:
> On Jan 8, 2008 6:59 AM, Andrew Cagney <address@hidden 
> <mailto:address@hidden>> wrote:
>
>     1.98c worth:
>
>     - the "CFA" value is from the frame inner to cursor
>     can I suggest a name like UNW_REG_INNER_CFA?
>
>
> Is there an ambiguity that the longer name helps resolve?
Consider:

  foo() -- inner
  bar()
  main() - outer

and:

  bar_cursor = foo_cursor
  step(&bar_cursor)

so that bar's inner is foo; then foo's CFA can only be obtained by:

  bar_cursor.get(UNW_REG_INNER_CFA)

and not:

  foo_cursor.get(UNW_REG_CFA)

This is because foo's CFA is only computed when stepping the cursor to 
bar  (and the computed value is saved in bar).

Andrew


>     - can it be assigned a negative constant value so that it can't polute
>     the ISA register number space
>     when extending the x86 register numbers I had to leave a gap in the
>     middle to ensure "binary" number compatibility, giving these libunwind
>     "registers" constant -ve values would help avoid that in the future 
>
>
> This sounds like a good thing to do.
>
> But because we have other libunwind registers (eg: UNW_TDEP_IP) whose 
> values change when new ISA registers are added, this should be a 
> separate patch.
>
>  -Arun
>