Hi
When GCC generates virtual methods for objects with multiple inheritance, it
creates special "thunk" functions that adjust this pointer and jump to an
original method.
When a member function returns a structure, the first argument is a pointer
where return structure should be placed, the second argument is "this" pointer
and additional arguments are arguments of the member function. When using
regparm 2 or 3, the first argument (ptr to return structure) is in EAX, the
second argument (this) is in EDX and additional arguments are in ECX and on the
stack.
The thunking function is generated incorrectly and always tries to adjust EAX,
causing corruption to this pointer and to the return value.
Similarly, when using fastcall convention, the pointer to return structure is
in ECX and this is in EDX, however thunking function adjusts ECX.
This bug is present in all GCC releases.
--
Summary: incorrect code generated on i386 for C++ multiple
inheritance, large return structures and regparm or
fastcall calling conventions
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: mikulas at artax dot karlin dot mff dot cuni dot cz
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35504
