Re: [rfa/6.0] Better handle unspecified CFI values

Daniel Jacobowitz
2003-09-06T21:34:16Z

On Fri, Sep 05, 2003 at 08:57:57PM -0400, Andrew Cagney wrote:
> Hello,
>
> This patch is an attempt at improving GDB's behavior when GCC "treads
> the boundaries of the CFI specification".
>
> It does the following:
>
> - changes the rules REG_UNMODIFIED -> REG_SAME_VALUE and REG_UNSAVED ->
> REG_UNDEFINED so that they better match the corresponding CFI register
> states (I could commit this separatly). The other names confused me :-)
>
> - it adds a new register rule - REG_UNSPECIFIED - which is used to
> differentiate a register that is missing CFI info from a register that
> CFI specified as "undefined" (nee UNSAVED).
>
> - when unwinding, it treats REG_UNSPECIFIED registers like
> REG_SAME_VALUE but with the additional hack to map an unspecified
> SP_REGNUM onto the CFA.
>
> - if it detects an unspecified CFI entry it complains
> It isn't perfect though - since it doesn't know the full range of valid
> debug info register numbers it can't check every entry. Instead it
> checks the range provided by CFI for unspecified holes and then
> complains about that. The reality is that GCC at least gets that bit
> right (but consistently forgets the SP).
>
> I'd like to commit the patch as is for the 6.0 branch. For the mainline
> though, I'd like to make the additional changes:
>
> - delete the SP_REGNUM hack from the REG_UNDEFINED rule (it's no longer
> needed, I think)

Leaving the hack in REG_UNSPECIFIED? Yes, I'm pretty sure you're
right.

> - add a check/complaint for the SP v CFA problem.

Could you hold off on the complaint until there's a valid way to
specify the SP in the unwind information? Right now there isn't one,
as I described on the dwarf2 list three weeks ago.

Otherwise this looks good to me.

> @@ -611,7 +646,9 @@
>
> switch (cache->reg[regnum].how)
> {
> - case REG_UNSAVED:
> + case REG_UNDEFINED:
> + /* If CFI explicitly specified that the value isn't defined,
> + mark it as optomized away - the value isn't available. */

"optimized"

--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer