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tdep/1388: use_struct_convention -> return_value
- From: ac131313 at redhat dot com
- To: gdb-gnats at sources dot redhat dot com
- Date: 21 Sep 2003 14:44:07 -0000
- Subject: tdep/1388: use_struct_convention -> return_value
- Reply-to: ac131313 at redhat dot com
>Number: 1388
>Category: tdep
>Synopsis: use_struct_convention -> return_value
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: maintenance
>Submitter-Id: net
>Arrival-Date: Sun Sep 21 14:48:01 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator: ac131313@redhat.com
>Release: unknown-1.0
>Organization:
>Environment:
>Description:
GDB currently has four (use_struct_convention, extract_return_value, store_return_value, return_value_on_stack) methods, and half a function (using_struct_return) that know the ABIs return-value conventions. That leads to 4 1/2 variations of the code needed to determine the location of a return-value.
Recommend a new method:
int ->return_value (return_type, regcache, inval, outval)
(return_type might be replaced by function type?) that:
- returns non-zero if the return-value is in registers
- stores the return-value INVAL in REGCACHE, if INVAL is non-NULL
- stores the register return-value in OUTVAL, if OUTVAL is non-NULL
This lets the programmer use the coding style:
if (return_type in registers X:Y:Z)
{
if (inval != NULL)
copy INVAL to REGCACHE X:Y:Z
if (outval != NULL)
copy REGCACHE X:Y:Z to OUTVAL
return 1;
}
if (return_type in registers A:B:C)
....
/* Not in a register. */
return 0;
There is a tradeoff here - the old model had the "is this in a register?" logic triplicated while the new code has the "read?, write", query?" logic triplicated. Given that the bugs are invariably in the "in a register?" (the abi spec) eliminating that triplication should make GDB more robust.
Notes:
- The new method should swallow much of set_return_value, and using_struct_return
- There is the potential for many return-value location states: found, not found X on stack, by ref, by register. This interface only covers: found && by register, not found && by ref. I can't find code dependant on those additional states.
See the ppc64_sysv_abi_return_value posted to gdb-patches for a full example.
>How-To-Repeat:
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted: