cmd/link: add relocation type R_AARCH64_LDST16_ABS_LO12_NC for arm64

The linker already has R_AARCH64_LDST{8,32,64,128}_ABS_LO12_NC, some cgo tests require
 R_AARCH64_LDST16_ABS_LO12_NC, this CL adds this relocation type.

Fixes #42660

Change-Id: I9a5120cd872f5095c61175cb602427c6ab3225cc
Reviewed-on: https://go-review.googlesource.com/c/go/+/271017
Reviewed-by: eric fang <eric.fang@arm.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: eric fang <eric.fang@arm.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: eric fang <eric.fang@arm.com>
Trust: Benny Siegert <bsiegert@gmail.com>
diff --git a/src/cmd/internal/objabi/reloctype.go b/src/cmd/internal/objabi/reloctype.go
index 938954e..649f690 100644
--- a/src/cmd/internal/objabi/reloctype.go
+++ b/src/cmd/internal/objabi/reloctype.go
@@ -156,6 +156,9 @@
 	// R_ARM64_LDST8 sets a LD/ST immediate value to bits [11:0] of a local address.
 	R_ARM64_LDST8
 
+	// R_ARM64_LDST16 sets a LD/ST immediate value to bits [11:1] of a local address.
+	R_ARM64_LDST16
+
 	// R_ARM64_LDST32 sets a LD/ST immediate value to bits [11:2] of a local address.
 	R_ARM64_LDST32
 
diff --git a/src/cmd/internal/objabi/reloctype_string.go b/src/cmd/internal/objabi/reloctype_string.go
index 693d963..658a44f 100644
--- a/src/cmd/internal/objabi/reloctype_string.go
+++ b/src/cmd/internal/objabi/reloctype_string.go
@@ -46,32 +46,33 @@
 	_ = x[R_ARM64_GOT-36]
 	_ = x[R_ARM64_PCREL-37]
 	_ = x[R_ARM64_LDST8-38]
-	_ = x[R_ARM64_LDST32-39]
-	_ = x[R_ARM64_LDST64-40]
-	_ = x[R_ARM64_LDST128-41]
-	_ = x[R_POWER_TLS_LE-42]
-	_ = x[R_POWER_TLS_IE-43]
-	_ = x[R_POWER_TLS-44]
-	_ = x[R_ADDRPOWER_DS-45]
-	_ = x[R_ADDRPOWER_GOT-46]
-	_ = x[R_ADDRPOWER_PCREL-47]
-	_ = x[R_ADDRPOWER_TOCREL-48]
-	_ = x[R_ADDRPOWER_TOCREL_DS-49]
-	_ = x[R_RISCV_PCREL_ITYPE-50]
-	_ = x[R_RISCV_PCREL_STYPE-51]
-	_ = x[R_RISCV_TLS_IE_ITYPE-52]
-	_ = x[R_RISCV_TLS_IE_STYPE-53]
-	_ = x[R_PCRELDBL-54]
-	_ = x[R_ADDRMIPSU-55]
-	_ = x[R_ADDRMIPSTLS-56]
-	_ = x[R_ADDRCUOFF-57]
-	_ = x[R_WASMIMPORT-58]
-	_ = x[R_XCOFFREF-59]
+	_ = x[R_ARM64_LDST16-39]
+	_ = x[R_ARM64_LDST32-40]
+	_ = x[R_ARM64_LDST64-41]
+	_ = x[R_ARM64_LDST128-42]
+	_ = x[R_POWER_TLS_LE-43]
+	_ = x[R_POWER_TLS_IE-44]
+	_ = x[R_POWER_TLS-45]
+	_ = x[R_ADDRPOWER_DS-46]
+	_ = x[R_ADDRPOWER_GOT-47]
+	_ = x[R_ADDRPOWER_PCREL-48]
+	_ = x[R_ADDRPOWER_TOCREL-49]
+	_ = x[R_ADDRPOWER_TOCREL_DS-50]
+	_ = x[R_RISCV_PCREL_ITYPE-51]
+	_ = x[R_RISCV_PCREL_STYPE-52]
+	_ = x[R_RISCV_TLS_IE_ITYPE-53]
+	_ = x[R_RISCV_TLS_IE_STYPE-54]
+	_ = x[R_PCRELDBL-55]
+	_ = x[R_ADDRMIPSU-56]
+	_ = x[R_ADDRMIPSTLS-57]
+	_ = x[R_ADDRCUOFF-58]
+	_ = x[R_WASMIMPORT-59]
+	_ = x[R_XCOFFREF-60]
 }
 
-const _RelocType_name = "R_ADDRR_ADDRPOWERR_ADDRARM64R_ADDRMIPSR_ADDROFFR_WEAKADDROFFR_SIZER_CALLR_CALLARMR_CALLARM64R_CALLINDR_CALLPOWERR_CALLMIPSR_CALLRISCVR_CONSTR_PCRELR_TLS_LER_TLS_IER_GOTOFFR_PLT0R_PLT1R_PLT2R_USEFIELDR_USETYPER_USEIFACER_USEIFACEMETHODR_METHODOFFR_POWER_TOCR_GOTPCRELR_JMPMIPSR_DWARFSECREFR_DWARFFILEREFR_ARM64_TLS_LER_ARM64_TLS_IER_ARM64_GOTPCRELR_ARM64_GOTR_ARM64_PCRELR_ARM64_LDST8R_ARM64_LDST32R_ARM64_LDST64R_ARM64_LDST128R_POWER_TLS_LER_POWER_TLS_IER_POWER_TLSR_ADDRPOWER_DSR_ADDRPOWER_GOTR_ADDRPOWER_PCRELR_ADDRPOWER_TOCRELR_ADDRPOWER_TOCREL_DSR_RISCV_PCREL_ITYPER_RISCV_PCREL_STYPER_RISCV_TLS_IE_ITYPER_RISCV_TLS_IE_STYPER_PCRELDBLR_ADDRMIPSUR_ADDRMIPSTLSR_ADDRCUOFFR_WASMIMPORTR_XCOFFREF"
+const _RelocType_name = "R_ADDRR_ADDRPOWERR_ADDRARM64R_ADDRMIPSR_ADDROFFR_WEAKADDROFFR_SIZER_CALLR_CALLARMR_CALLARM64R_CALLINDR_CALLPOWERR_CALLMIPSR_CALLRISCVR_CONSTR_PCRELR_TLS_LER_TLS_IER_GOTOFFR_PLT0R_PLT1R_PLT2R_USEFIELDR_USETYPER_USEIFACER_USEIFACEMETHODR_METHODOFFR_POWER_TOCR_GOTPCRELR_JMPMIPSR_DWARFSECREFR_DWARFFILEREFR_ARM64_TLS_LER_ARM64_TLS_IER_ARM64_GOTPCRELR_ARM64_GOTR_ARM64_PCRELR_ARM64_LDST8R_ARM64_LDST16R_ARM64_LDST32R_ARM64_LDST64R_ARM64_LDST128R_POWER_TLS_LER_POWER_TLS_IER_POWER_TLSR_ADDRPOWER_DSR_ADDRPOWER_GOTR_ADDRPOWER_PCRELR_ADDRPOWER_TOCRELR_ADDRPOWER_TOCREL_DSR_RISCV_PCREL_ITYPER_RISCV_PCREL_STYPER_RISCV_TLS_IE_ITYPER_RISCV_TLS_IE_STYPER_PCRELDBLR_ADDRMIPSUR_ADDRMIPSTLSR_ADDRCUOFFR_WASMIMPORTR_XCOFFREF"
 
-var _RelocType_index = [...]uint16{0, 6, 17, 28, 38, 47, 60, 66, 72, 81, 92, 101, 112, 122, 133, 140, 147, 155, 163, 171, 177, 183, 189, 199, 208, 218, 234, 245, 256, 266, 275, 288, 302, 316, 330, 346, 357, 370, 383, 397, 411, 426, 440, 454, 465, 479, 494, 511, 529, 550, 569, 588, 608, 628, 638, 649, 662, 673, 685, 695}
+var _RelocType_index = [...]uint16{0, 6, 17, 28, 38, 47, 60, 66, 72, 81, 92, 101, 112, 122, 133, 140, 147, 155, 163, 171, 177, 183, 189, 199, 208, 218, 234, 245, 256, 266, 275, 288, 302, 316, 330, 346, 357, 370, 383, 397, 411, 425, 440, 454, 468, 479, 493, 508, 525, 543, 564, 583, 602, 622, 642, 652, 663, 676, 687, 699, 709}
 
 func (i RelocType) String() string {
 	i -= 1
diff --git a/src/cmd/link/internal/arm64/asm.go b/src/cmd/link/internal/arm64/asm.go
index cb16180..a7af855 100644
--- a/src/cmd/link/internal/arm64/asm.go
+++ b/src/cmd/link/internal/arm64/asm.go
@@ -177,6 +177,14 @@
 		su.SetRelocType(rIdx, objabi.R_ARM64_LDST8)
 		return true
 
+	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_AARCH64_LDST16_ABS_LO12_NC):
+		if targType == sym.SDYNIMPORT {
+			ldr.Errorf(s, "unexpected relocation for dynamic symbol %s", ldr.SymName(targ))
+		}
+		su := ldr.MakeSymbolUpdater(s)
+		su.SetRelocType(rIdx, objabi.R_ARM64_LDST16)
+		return true
+
 	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_AARCH64_LDST32_ABS_LO12_NC):
 		if targType == sym.SDYNIMPORT {
 			ldr.Errorf(s, "unexpected relocation for dynamic symbol %s", ldr.SymName(targ))
@@ -769,6 +777,14 @@
 		o0 := uint32(t&0xfff) << 10
 		return val | int64(o0), noExtReloc, true
 
+	case objabi.R_ARM64_LDST16:
+		t := ldr.SymAddr(rs) + r.Add() - ((ldr.SymValue(s) + int64(r.Off())) &^ 0xfff)
+		if t&1 != 0 {
+			ldr.Errorf(s, "invalid address: %x for relocation type: R_AARCH64_LDST16_ABS_LO12_NC", t)
+		}
+		o0 := (uint32(t&0xfff) >> 1) << 10
+		return val | int64(o0), noExtReloc, true
+
 	case objabi.R_ARM64_LDST32:
 		t := ldr.SymAddr(rs) + r.Add() - ((ldr.SymValue(s) + int64(r.Off())) &^ 0xfff)
 		if t&3 != 0 {
diff --git a/src/cmd/link/internal/loadelf/ldelf.go b/src/cmd/link/internal/loadelf/ldelf.go
index 5260c6b..db543a5 100644
--- a/src/cmd/link/internal/loadelf/ldelf.go
+++ b/src/cmd/link/internal/loadelf/ldelf.go
@@ -1019,6 +1019,7 @@
 		ARM64 | uint32(elf.R_AARCH64_ADR_PREL_PG_HI21)<<16,
 		ARM64 | uint32(elf.R_AARCH64_ADD_ABS_LO12_NC)<<16,
 		ARM64 | uint32(elf.R_AARCH64_LDST8_ABS_LO12_NC)<<16,
+		ARM64 | uint32(elf.R_AARCH64_LDST16_ABS_LO12_NC)<<16,
 		ARM64 | uint32(elf.R_AARCH64_LDST32_ABS_LO12_NC)<<16,
 		ARM64 | uint32(elf.R_AARCH64_LDST64_ABS_LO12_NC)<<16,
 		ARM64 | uint32(elf.R_AARCH64_LDST128_ABS_LO12_NC)<<16,