runtime: add support for --buildmode=c-shared on loong64

These c-shared related CLs are follow up of CLs 455016, 455017, 455018. Here we
follow the LoongArch ELF psABI v2 standard, which requires the support of the
PCALAU12I instruction.

Updates golang#53301
Updates golang#58784

Change-Id: I7f1ddbf3b2470d610f12069d147aa9b3a6a96f32

src/runtime/cgo/abi_loong64.h

@@ -0,0 +1,67 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Macros for transitioning from the host ABI to Go ABI0.
+//
+// These save the frame pointer, so in general, functions that use
+// these should have zero frame size to suppress the automatic frame
+// pointer, though it's harmless to not do this.
+
+#define PUSH_REGS_FLOAT_PART() \
+	MOVD	F18, 120(R3) \
+	MOVD	F19, 128(R3) \
+	MOVD	F20, 136(R3) \
+	MOVD	F21, 144(R3) \
+	MOVD	F24, 152(R3) \
+	MOVD	F25, 160(R3) \
+	MOVD	F26, 168(R3) \
+	MOVD	F27, 176(R3) \
+	MOVD	F28, 184(R3) \
+	MOVD	F29, 192(R3) \
+	MOVD	F30, 200(R3) \
+	MOVD	F31, 208(R3)
+
+#define POP_REGS_FLOAT_PART() \
+	MOVD	120(R3), F18 \
+	MOVD	128(R3), F19 \
+	MOVD	136(R3), F20 \
+	MOVD	144(R3), F21 \
+	MOVD	152(R3), F24 \
+	MOVD	160(R3), F25 \
+	MOVD	168(R3), F26 \
+	MOVD	176(R3), F27 \
+	MOVD	184(R3), F28 \
+	MOVD	192(R3), F29 \
+	MOVD	200(R3), F30 \
+	MOVD	208(R3), F31
+
+#define PUSH_REGS_HOST_TO_ABI0() \
+	MOVV    R23, 24(R3) \
+	MOVV    R24, 32(R3) \
+	MOVV    R25, 40(R3) \
+	MOVV    R26, 48(R3) \
+	MOVV    R27, 56(R3) \
+	MOVV    R28, 64(R3) \
+	MOVV    R29, 72(R3) \
+	MOVV    R30, 80(R3) \
+	MOVV    R31, 88(R3) \
+	MOVV    R3, 96(R3) \
+	MOVV    g, 104(R3) \
+	MOVV    R1, 112(R3) \
+	PUSH_REGS_FLOAT_PART()
+
+#define POP_REGS_HOST_TO_ABI0() \
+	MOVV    24(R3), R23 \
+	MOVV    32(R3), R24 \
+	MOVV    40(R3), R25 \
+	MOVV    48(R3), R26 \
+	MOVV    56(R3), R27 \
+	MOVV    64(R3), R28 \
+	MOVV    72(R3), R29 \
+	MOVV    80(R3), R30 \
+	MOVV    88(R3), R31 \
+	MOVV    96(R3), R3 \
+	MOVV    104(R3), g \
+	MOVV    112(R3), R1 \
+	POP_REGS_FLOAT_PART()

src/runtime/rt0_linux_loong64.s

@@ -3,6 +3,7 @@
 // license that can be found in the LICENSE file.
 
 #include "textflag.h"
+#include "cgo/abi_loong64.h"
 
 TEXT _rt0_loong64_linux(SB),NOSPLIT,$0
 	JMP	_main<>(SB)
@@ -16,6 +17,54 @@ TEXT _main<>(SB),NOSPLIT|NOFRAME,$0
 	ADDV	$8, R3, R5 // argv
 	JMP	main(SB)
 
+// When building with -buildmode=c-shared, this symbol is called when the shared
+// library is loaded.
+TEXT _rt0_loong64_linux_lib(SB),NOSPLIT,$232
+	// Preserve callee-save registers.
+	PUSH_REGS_HOST_TO_ABI0()
+
+	// Initialize g as null in case of using g later e.g. sigaction in cgo_sigaction.go
+	MOVV	R0, g
+
+	MOVV	R4, _rt0_loong64_linux_lib_argc<>(SB)
+	MOVV	R5, _rt0_loong64_linux_lib_argv<>(SB)
+
+	// Synchronous initialization.
+	MOVV	$runtime·libpreinit(SB), R19
+	JAL     (R19)
+
+	// Create a new thread to do the runtime initialization and return.
+	MOVV	_cgo_sys_thread_create(SB), R19
+	BEQ     R19, nocgo
+	MOVV	$_rt0_loong64_linux_lib_go(SB), R4
+	MOVV	$0, R5
+	JAL     (R19)
+	JMP     restore
+
+nocgo:
+	MOVV	$0x800000, R4                     // stacksize = 8192KB
+	MOVV	$_rt0_loong64_linux_lib_go(SB), R5
+	MOVV	R4, 8(R3)
+	MOVV	R5, 16(R3)
+	MOVV	$runtime·newosproc0(SB), R19
+	JAL     (R19)
+
+restore:
+	// Restore callee-save registers.
+	POP_REGS_HOST_TO_ABI0()
+	RET
+
+TEXT _rt0_loong64_linux_lib_go(SB),NOSPLIT,$0
+	MOVV	_rt0_loong64_linux_lib_argc<>(SB), R4
+	MOVV	_rt0_loong64_linux_lib_argv<>(SB), R5
+	MOVV	$runtime·rt0_go(SB),R19
+	JMP     (R19)
+
+DATA _rt0_loong64_linux_lib_argc<>(SB)/8, $0
+GLOBL _rt0_loong64_linux_lib_argc<>(SB),NOPTR, $8
+DATA _rt0_loong64_linux_lib_argv<>(SB)/8, $0
+GLOBL _rt0_loong64_linux_lib_argv<>(SB),NOPTR, $8
+
 TEXT main(SB),NOSPLIT|NOFRAME,$0
 	// in external linking, glibc jumps to main with argc in R4
 	// and argv in R5

src/runtime/tls_loong64.s

@@ -2,20 +2,13 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-#include "go_asm.h"
-#include "go_tls.h"
-#include "funcdata.h"
 #include "textflag.h"
 
 // If !iscgo, this is a no-op.
-//
-// NOTE: mcall() assumes this clobbers only R30 (REGTMP).
 TEXT runtime·save_g(SB),NOSPLIT|NOFRAME,$0-0
 	MOVB	runtime·iscgo(SB), R30
 	BEQ	R30, nocgo
-
 	MOVV	g, runtime·tls_g(SB)
-
 nocgo:
 	RET