On 03/28/2012 09:10 AM, Ajinkya Dhobale wrote:
Hi Jeff,
Thank you for replying to the post.
How is this different than the function vector support that is
already in GCC for the H8/300 series processors?
Current H8/300 implementation of function vector seems inappropriate.
This patch fixes following problems from it.
1. Attribute syntax:
The function vector attribute is expected to accept one argument i.e.
vector number.
Ref: http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#index-
calling-functions-through-the-function-vector-on-H8_002f300_002c-
M16C_002c-M32C-and-SH2A-processors-2525
However, with H8/300 target, it does not accept any argument and test case
compilation fails with an error message:
error: wrong number of arguments specified for function_vector attribute
This patch fixes this problem.
Ok. So the fundamental difference is your version of function_vector is
programmer directed. ie, the programmer explicitly assigns slots for
functions to call through the function vector.
The existing implementation relies upon the linker to handle assignment
of a specific slot.
The problem with installing your patch as-is is it will break existing
code which utilizes the linker driven assignment of slots.
ISTM that you either need to use a different attribute name or find a
way to make the argument optional.
2. Addressing mode support:
Currently, even for function vectors, GCC generates instruction 'jsr'
in absolute addressing mode which is incorrect. Instead of that, it should be
generating 'jsr' in indirect memory addressing mode (@@aa:8).
I think you need to investigate further since functions marked with the
attribute should be called through the function vector.
When the linker assigns the slot, the proper syntax is jsr <name>:8
Obviously for the programmer assigned slots, you'll need to use a
different syntax. But simply removing the linker assigned slot support
is wrong.
Jeff
