On 16.07.2019 13:05, christoph.goettschkes@microdoc.com wrote:
> while working with the OpenJDK 11 on a 32-bit ARMv7-A platform, I noticed
> something weird in the template interpreter, regarding the template for
> the bytecode instruction ldc2_w.
>
> The type check for the operand is only done correctly if the ABI is a
> hard-float one. For soft-float, the check is done wrong, using an
> uninitialized register Rtemp. Please see the following diff:
>
> diff -r 327d5994b2fb src/hotspot/cpu/arm/templateTable_arm.cpp
> --- a/src/hotspot/cpu/arm/templateTable_arm.cpp Tue Mar 12 11:13:39 2019 -0400
> +++ b/src/hotspot/cpu/arm/templateTable_arm.cpp Tue Jul 16 11:22:14 2019 +0200
> @@ -515,36 +515,37 @@
> void TemplateTable::ldc2_w() {
> transition(vtos, vtos);
> const Register Rtags = R2_tmp;
> const Register Rindex = R3_tmp;
> const Register Rcpool = R4_tmp;
> const Register Rbase = R5_tmp;
>
> __ get_unsigned_2_byte_index_at_bcp(Rindex, 1);
>
> __ get_cpool_and_tags(Rcpool, Rtags);
> const int base_offset = ConstantPool::header_size() * wordSize;
> const int tags_offset = Array<u1>::base_offset_in_bytes();
>
> __ add(Rbase, Rcpool, AsmOperand(Rindex, lsl, LogBytesPerWord));
>
> + // get type from tags
> + __ add(Rtemp, Rtags, tags_offset);
> + __ ldrb(Rtemp, Address(Rtemp, Rindex));
> +
> Label Condy, exit;
> #ifdef __ABI_HARD__
> Label Long;
> - // get type from tags
> - __ add(Rtemp, Rtags, tags_offset);
> - __ ldrb(Rtemp, Address(Rtemp, Rindex));
> __ cmp(Rtemp, JVM_CONSTANT_Double);
> __ b(Long, ne);
> __ ldr_double(D0_tos, Address(Rbase, base_offset));
>
> __ push(dtos);
> __ b(exit);
> __ bind(Long);
> #endif
>
> __ cmp(Rtemp, JVM_CONSTANT_Long);
> __ b(Condy, ne);
> #ifdef AARCH64
> __ ldr(R0_tos, Address(Rbase, base_offset));
> #else
> __ ldr(R0_tos_lo, Address(Rbase, base_offset + 0 * wordSize));
>
> If the check for the type of the operand is done correctly, the call to
> InterpreterRuntime::resolve_ldc should never happen. Currently, for 32-bit
> soft-float arm, InterpreterRuntime::resolve_ldc is called if the operand
> for ldc2_w is of type long.
>
> Also, I find it weird that the "condy_helper" code is genarted for the
> ldc2_w bytecode instruction on 32-bit hard-float arm (and also on x86).
> Aren't the only two valid types for ldc2_w long and double?
>
> -- Christoph