RFR: 8350182: [s390x] Relativize locals in interpreter frames

[Amit Kumar]

On Mon, 17 Feb 2025 09:53:37 GMT, Amit Kumar <amitkumar at openjdk.org> wrote:

> Port for [JDK-8299795](https://bugs.openjdk.org/browse/JDK-8299795) Relativize Z_locals in interpreter frame for s390x.
> 
> Tier1  test with fastdebug vm are clean.

src/hotspot/cpu/s390/interp_masm_s390.cpp line 117:

> 115:     z_agr(Z_R1_scratch, Z_fp);
> 116: 
> 117:     z_cgr(Z_locals, Z_R1_scratch);

By default assertion was failing, Because stored value is fp relativised and Z_locals is holding pointer. So I have updated it. 

I have done some manual step through and found that it should be okay to keep, unless we don't want to kill another register here. 

diff --git a/src/hotspot/cpu/s390/templateInterpreterGenerator_s390.cpp b/src/hotspot/cpu/s390/templateInterpreterGenerator_s390.cpp
index c40be5edec7..fc5b9f10af1 100644
--- a/src/hotspot/cpu/s390/templateInterpreterGenerator_s390.cpp
+++ b/src/hotspot/cpu/s390/templateInterpreterGenerator_s390.cpp
@@ -1134,8 +1134,16 @@ void TemplateInterpreterGenerator::generate_fixed_frame(bool native_call) {
   __ z_agr(Z_locals, Z_esp);
   // z_ijava_state->locals - i*BytesPerWord points to i-th Java local (i starts at 0)
   // z_ijava_state->locals = Z_esp + parameter_count bytes

+  __ z_sgrk(Z_locals, Z_locals, fp); // Z_R1 = Z_locals - fp();
+  __ z_srlg(Z_locals, Z_locals, Interpreter::logStackElementSize);
+  // Store relativized Z_locals, see frame::interpreter_frame_locals().
   __ z_stg(Z_locals, _z_ijava_state_neg(locals), fp);
   // z_ijava_state->oop_temp = nullptr;
   __ store_const(Address(fp, oop_tmp_offset), 0);


with this change, `Z_locals` is holding the correct value (fp relativized) which is stored at the state offset: 

(gdb) i r r12 
r12            0x1                 1
(gdb) x/2gx $r9 - 88 
0x3fffb37be98:	0x0000000000000001	0x000003fffb37be80
(gdb)




Similarly, with the change I have pushed: 

instr:

0x3fff8192b5a:	lg	%r1,-88(%r9)
0x3fff8192b60:	sllg	%r1,%r1,3
0x3fff8192b66:	agr	%r1,%r9


result: 

(gdb) i r r12 
r12            0x3fffb37bef8       4397966278392
(gdb) i r r1 
r1             0x3fffb37bef8       4397966278392
(gdb)

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/23660#discussion_r1957988781