cmd/link: support loading R_LARCH_PCREL20_S2 and R_LARCH_CALL36 relocs

Host libgcc.a (among other libraries) on loong64 systems may contain
such relocs if built with the "medium" code model and/or linker
relaxation, which is increasingly the case. Make the internal linker
aware of these for cgo interopability going forward.

While at it, fix some of the comments for the loong64-specific
RelocTypes.

Fixes #75562

Change-Id: I0810969dcd229c5131ef06b0f70f51d81a3be4cd
Reviewed-on: https://go-review.googlesource.com/c/go/+/709717
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Mark Freeman <markfreeman@google.com>
Reviewed-by: Meidan Li <limeidan@loongson.cn>
Reviewed-by: Junyang Shao <shaojunyang@google.com>

2 files changed, 48 insertions, 11 deletions

diff --git a/src/cmd/link/internal/loadelf/ldelf.go b/src/cmd/link/internal/loadelf/ldelf.go
index 1c83f03a5d..8f4c1a5765 100644
--- a/src/cmd/link/internal/loadelf/ldelf.go
+++ b/src/cmd/link/internal/loadelf/ldelf.go
@@ -1065,13 +1065,15 @@ func relSize(arch *sys.Arch, pn string, elftype uint32) (uint8, uint8, error) {
 		LOONG64 | uint32(elf.R_LARCH_PCALA_LO12)<<16,
 		LOONG64 | uint32(elf.R_LARCH_GOT_PC_HI20)<<16,
 		LOONG64 | uint32(elf.R_LARCH_GOT_PC_LO12)<<16,
-		LOONG64 | uint32(elf.R_LARCH_32_PCREL)<<16:
+		LOONG64 | uint32(elf.R_LARCH_32_PCREL)<<16,
+		LOONG64 | uint32(elf.R_LARCH_PCREL20_S2)<<16:
 		return 4, 4, nil
 
 	case LOONG64 | uint32(elf.R_LARCH_64)<<16,
 		LOONG64 | uint32(elf.R_LARCH_ADD64)<<16,
 		LOONG64 | uint32(elf.R_LARCH_SUB64)<<16,
-		LOONG64 | uint32(elf.R_LARCH_64_PCREL)<<16:
+		LOONG64 | uint32(elf.R_LARCH_64_PCREL)<<16,
+		LOONG64 | uint32(elf.R_LARCH_CALL36)<<16:
 		return 8, 8, nil
 
 	case S390X | uint32(elf.R_390_8)<<16:
diff --git a/src/cmd/link/internal/loong64/asm.go b/src/cmd/link/internal/loong64/asm.go
index e7f3fd1d98..219cfc7196 100644
--- a/src/cmd/link/internal/loong64/asm.go
+++ b/src/cmd/link/internal/loong64/asm.go
@@ -85,7 +85,8 @@ func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loade
 		}
 		return true
 
-	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_LARCH_B26):
+	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_LARCH_B26),
+		objabi.ElfRelocOffset + objabi.RelocType(elf.R_LARCH_CALL36):
 		if targType == sym.SDYNIMPORT {
 			addpltsym(target, ldr, syms, targ)
 			su := ldr.MakeSymbolUpdater(s)
@@ -95,8 +96,12 @@ func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loade
 		if targType == 0 || targType == sym.SXREF {
 			ldr.Errorf(s, "unknown symbol %s in callloong64", ldr.SymName(targ))
 		}
+		relocType := objabi.R_CALLLOONG64
+		if r.Type() == objabi.ElfRelocOffset+objabi.RelocType(elf.R_LARCH_CALL36) {
+			relocType = objabi.R_LOONG64_CALL36
+		}
 		su := ldr.MakeSymbolUpdater(s)
-		su.SetRelocType(rIdx, objabi.R_CALLLOONG64)
+		su.SetRelocType(rIdx, relocType)
 		return true
 
 	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_LARCH_GOT_PC_HI20),
@@ -117,7 +122,8 @@ func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loade
 		return true
 
 	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_LARCH_PCALA_HI20),
-		objabi.ElfRelocOffset + objabi.RelocType(elf.R_LARCH_PCALA_LO12):
+		objabi.ElfRelocOffset + objabi.RelocType(elf.R_LARCH_PCALA_LO12),
+		objabi.ElfRelocOffset + objabi.RelocType(elf.R_LARCH_PCREL20_S2):
 		if targType == sym.SDYNIMPORT {
 			ldr.Errorf(s, "unexpected relocation for dynamic symbol %s", ldr.SymName(targ))
 		}
@@ -125,12 +131,17 @@ func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loade
 			ldr.Errorf(s, "unknown symbol %s", ldr.SymName(targ))
 		}
 
-		su := ldr.MakeSymbolUpdater(s)
-		if r.Type() == objabi.ElfRelocOffset+objabi.RelocType(elf.R_LARCH_PCALA_HI20) {
-			su.SetRelocType(rIdx, objabi.R_LOONG64_ADDR_HI)
-		} else {
-			su.SetRelocType(rIdx, objabi.R_LOONG64_ADDR_LO)
+		var relocType objabi.RelocType
+		switch r.Type() - objabi.ElfRelocOffset {
+		case objabi.RelocType(elf.R_LARCH_PCALA_HI20):
+			relocType = objabi.R_LOONG64_ADDR_HI
+		case objabi.RelocType(elf.R_LARCH_PCALA_LO12):
+			relocType = objabi.R_LOONG64_ADDR_LO
+		case objabi.RelocType(elf.R_LARCH_PCREL20_S2):
+			relocType = objabi.R_LOONG64_ADDR_PCREL20_S2
 		}
+		su := ldr.MakeSymbolUpdater(s)
+		su.SetRelocType(rIdx, relocType)
 		return true
 
 	case objabi.ElfRelocOffset + objabi.RelocType(elf.R_LARCH_ADD64),
@@ -418,6 +429,11 @@ func elfreloc1(ctxt *ld.Link, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym,
 		out.Write64(uint64(elf.R_LARCH_B26) | uint64(elfsym)<<32)
 		out.Write64(uint64(r.Xadd))
 
+	case objabi.R_LOONG64_CALL36:
+		out.Write64(uint64(sectoff))
+		out.Write64(uint64(elf.R_LARCH_CALL36) | uint64(elfsym)<<32)
+		out.Write64(uint64(r.Xadd))
+
 	case objabi.R_LOONG64_TLS_IE_HI:
 		out.Write64(uint64(sectoff))
 		out.Write64(uint64(elf.R_LARCH_TLS_IE_PC_HI20) | uint64(elfsym)<<32)
@@ -438,6 +454,11 @@ func elfreloc1(ctxt *ld.Link, out *ld.OutBuf, ldr *loader.Loader, s loader.Sym,
 		out.Write64(uint64(elf.R_LARCH_PCALA_HI20) | uint64(elfsym)<<32)
 		out.Write64(uint64(r.Xadd))
 
+	case objabi.R_LOONG64_ADDR_PCREL20_S2:
+		out.Write64(uint64(sectoff))
+		out.Write64(uint64(elf.R_LARCH_PCREL20_S2) | uint64(elfsym)<<32)
+		out.Write64(uint64(r.Xadd))
+
 	case objabi.R_LOONG64_GOT_HI:
 		out.Write64(uint64(sectoff))
 		out.Write64(uint64(elf.R_LARCH_GOT_PC_HI20) | uint64(elfsym)<<32)
@@ -463,7 +484,8 @@ func archreloc(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, r loade
 		default:
 			return val, 0, false
 		case objabi.R_LOONG64_ADDR_HI,
-			objabi.R_LOONG64_ADDR_LO:
+			objabi.R_LOONG64_ADDR_LO,
+			objabi.R_LOONG64_ADDR_PCREL20_S2:
 			// set up addend for eventual relocation via outer symbol.
 			rs, _ := ld.FoldSubSymbolOffset(ldr, rs)
 			rst := ldr.SymType(rs)
@@ -474,6 +496,7 @@ func archreloc(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, r loade
 		case objabi.R_LOONG64_TLS_LE_HI,
 			objabi.R_LOONG64_TLS_LE_LO,
 			objabi.R_CALLLOONG64,
+			objabi.R_LOONG64_CALL36,
 			objabi.R_JMPLOONG64,
 			objabi.R_LOONG64_TLS_IE_HI,
 			objabi.R_LOONG64_TLS_IE_LO,
@@ -499,6 +522,10 @@ func archreloc(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, r loade
 			return val&0xffc003ff | (t << 10), noExtReloc, isOk
 		}
 		return val&0xfe00001f | (t << 5), noExtReloc, isOk
+	case objabi.R_LOONG64_ADDR_PCREL20_S2:
+		pc := ldr.SymValue(s) + int64(r.Off())
+		t := (ldr.SymAddr(rs) + r.Add() - pc) >> 2
+		return val&0xfe00001f | ((t & 0xfffff) << 5), noExtReloc, isOk
 	case objabi.R_LOONG64_TLS_LE_HI,
 		objabi.R_LOONG64_TLS_LE_LO:
 		t := ldr.SymAddr(rs) + r.Add()
@@ -512,6 +539,14 @@ func archreloc(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, r loade
 		t := ldr.SymAddr(rs) + r.Add() - pc
 		return val&0xfc000000 | (((t >> 2) & 0xffff) << 10) | (((t >> 2) & 0x3ff0000) >> 16), noExtReloc, isOk
 
+	case objabi.R_LOONG64_CALL36:
+		pc := ldr.SymValue(s) + int64(r.Off())
+		t := (ldr.SymAddr(rs) + r.Add() - pc) >> 2
+		// val is pcaddu18i (lower half) + jirl (upper half)
+		pcaddu18i := (val & 0xfe00001f) | (((t + 0x8000) >> 16) << 5)
+		jirl := ((val >> 32) & 0xfc0003ff) | ((t & 0xffff) << 10)
+		return pcaddu18i | (jirl << 32), noExtReloc, isOk
+
 	case objabi.R_JMP16LOONG64,
 		objabi.R_JMP21LOONG64:
 		pc := ldr.SymValue(s) + int64(r.Off())