[ColdFire 53/63] Static chain fixes

[Richard Sandiford]

Jeffrey Law <law@redhat.com> writes:
> On Wed, 2007-01-10 at 16:51 -0500, Andrew Pinski wrote:
>> > 
>> > On Wed, 2007-01-10 at 21:32 +0000, Paul Brook wrote:
>> > > > > 	* config/m68k/m68k.h (M68K_STATIC_CHAIN_REG_NAME): New macro.
>> > > > > 	(INITIALIZE_TRAMPOLINE): Use STATIC_CHAIN_REGNUM.
>> > > > > 	(__transfer_from_trampoline): Use M68K_STATIC_CHAIN_REG_NAME.
>> > > > > 	* config/m68k/m68kelf.h (STATIC_CHAIN_REGNUM): Override.
>> > > > > 	(M68K_STATIC_CHAIN_REG_NAME): Likewise.
>> > > > > 	* config/m68k/netbsd-elf.h (M68K_STATIC_CHAIN_REG_NAME): Likewise.
>> > > > >
>> > > > > gcc/testsuite/
>> > > > > 200x-xx-xx  Nathan Sidwell  <nathan@codesourcery.com>
>> > > > >
>> > > > > 	* gcc.c-torture/execute/nestfunc-7.c: New.
>> > > >
>> > > > Isn't this an ABI change?  If so it needs to be documented at the least
>> > > > so that users of the m68k elf port aren't caught by surprise.
>> > > 
>> > > I thought STATIC_CHAIN_REGNUM was an internal implementation detail.
>> > > It's a private interface between the trampoline and the nested function, and 
>> > > never escapes to the outside world.
>> > Doesn't the caller need to tell the callee where to find stacked
>> > variables?  It seems to me the caller and callee need to agree on
>> > that location.
>> 
>> Yes they have to agree but the only place which uses static chain are for
>> nested functions and nested functions are always local to the TU.
> Why must they be local.
>
> Take the address of a nested function and pass it as an argument to a
> function outside the current translation unit.  IIRC the only 
> restriction we've made on calling nested functions is that the
> container function must still be on the dynamic call stack.

But when we do that, we actually pass the address of a trampoline
function, which is just a black box as far as the other translation
unit is concerned.  That trampoline reads the static chain register
from memory (which is also part of the trampoline) and then calls
the real function.

Richard