[Bug target/60123] New: TIC6x: EABI incompatibility when large struct is returned from function and is not used by the caller

[wojtek.golf at interia dot pl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60123

            Bug ID: 60123
           Summary: TIC6x: EABI incompatibility when large struct is
                    returned from function and is not used by the caller
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: wojtek.golf at interia dot pl

=================================================================================
Exact version of gcc:
tic6x-none-elf-gcc (GCC) 4.9.0 20140208 (experimental)

================================================================================
System type:
Linux wmigda-desktop 3.11.0-13-generic #20-Ubuntu SMP Wed Oct 23 17:26:33 UTC
2013 i686 i686 i686 GNU/Linux

================================================================================
Options given when gcc was built:

export TRIPLET=tic6x-none-elf
mkdir -pv ${X_BUILD_DIR}/gcc-${GCC_VER}-build-pass-1/

pushd ${X_BUILD_DIR}gcc-${GCC_VER}-build-pass-1/ && \
RANLIB_FOR_TARGET=${CXTOOLS}bin/${TRIPLET}-ranlib
AS_FOR_TARGET=${CXTOOLS}bin/${TRIPLET}-as
AR_FOR_TARGET=${CXTOOLS}bin/${TRIPLET}-ar \
AS=as AR=ar LDFLAGS='-lstdc++ -lm' ../../../../gcc/configure \
--prefix=${C_TOOLS} \
--build=$(gcc -dumpmachine) \
--host=$(gcc -dumpmachine) \
--target=${TRIPLET} \
--with-local-prefix=${CXTOOLS}${TRIPLET}/sysroot \
--with-sysroot=${CXTOOLS}${TRIPLET}/sysroot \
--disable-nls \
--disable-shared \
--without-headers \
--with-newlib \
--disable-decimal-float \
--disable-libgomp \
--disable-libmudflap \
--disable-libssp \
--disable-libatomic \
--disable-libquadmath \
--disable-threads \
--enable-languages=c \
--disable-multilib \
--with-mpfr=${C_TOOLS} \
--with-gmp=${C_TOOLS} \
--disable-__cxa_atexit \
--disable-sjlj-exceptions \
--enable-target-optspace \
--disable-libstdcxx-pch \
; popd

================================================================================
Commandline:
tic6x-none-elf-gcc -fleading-underscore -march=c674x -O2 -g0 -S main.c

================================================================================
Compiler output:
nothing one the console

================================================================================
Preprocessed file:

# 1 "main.c"
# 1 "<command-line>"
# 1 "main.c"
typedef struct A
{
    long long y;
    char z;
} struct_A;

extern struct_A e_struct1;

struct_A g_fun_6(void)
{
    return e_struct1;
}

================================================================================
The problem:
SPRAB89 document from Texas Instruments states that:
"If the called function returns a structure or union larger than 64 bits, the
caller must pass an additional argument in A3 containing a destination address
for the returned value, or 0 if the returned value is not used. The callee
returns the object by copying it to the address in A3, if non-zero."

Assembler listing generated by gcc doesn't check for the passed address being
non-NULL:

_g_fun_6:
        mvkl    .s1 (_e_struct1), A5
    ||  mv  .d1 A3, A4
        mvkh    .s1 (_e_struct1), A5
        lddw    .d1t1   *A5, A7:A6
        lddw    .d1t1   *+A5(8), A9:A8
    ||  ret .s2 B3
        nop 3
        stdw    .d1t1   A7:A6, *A3
        stdw    .d1t1   A9:A8, *+A3(8)

whereas assembler generated by TI CGTools' cl6x compiler does. Hence, if the
code compiled with cl6x calls code produced by gcc a NULL pointer write will
occur.
Also, in the assembler above copying A3 to A4 (mv  .d1 A3, A4) doesn't relate
to anything and could be eliminated altogether.