feat(asm): emit the loong64 stack-split guard for big frames

asm/elfloong64.go

@@ -16,6 +16,7 @@ const (
 	// LoongArch relocation types (the ELF psABI).
 	rLarchPCALAHI20 = 71 // R_LARCH_PCALA_HI20 (pcalau12i)
 	rLarchPCALALO12 = 72 // R_LARCH_PCALA_LO12 (addi.d/ld/st)
+	rLarchB26       = 66 // R_LARCH_B26 (b/bl, matches the Go linker's mapping)
 )
 
 // ELFLOONG64Object returns the image as an ELF64 relocatable object file for
@@ -95,8 +96,11 @@ func (img *Image) ELFLOONG64Object() ([]byte, error) {
 				return nil, fmt.Errorf("relocation references unknown symbol %q", r.Name)
 			}
 			typ := uint32(rLarchPCALAHI20)
-			if r.Kind == RelLoong64AddrLo {
+			switch r.Kind {
+			case RelLoong64AddrLo:
 				typ = rLarchPCALALO12
+			case RelLoong64Branch:
+				typ = rLarchB26
 			}
 			relas = append(relas, elfRela{
 				off:    uint64(fn.Offset + r.Off),