cmd/link: load external ELF PPC64 objects which set st_other=1

This indicates the symbol does not use or preserve the TOC pointer in
R2. Likewise, it does not have a distinct local entry point. This
happens when gcc compiles an object with -mcpu=power10.

Recycle the SymLocalentry field of a text symbol to pass through this
hint as the bogus value 1 (A valid offset must be a multiple of 4
bytes), and update the usage to check and generate errors further into
the linking process. This matches the behavior of st_other as used by
ELFv2.

Change-Id: Ic89ce17b57f400ab44213b21a3730a98c7cdf842
Reviewed-on: https://go-review.googlesource.com/c/go/+/490295
Run-TryBot: Paul Murphy <murp@ibm.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/link/internal/loadelf/ldelf.go

@@ -639,11 +639,15 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, f *bio.Reader,
 			case 0:
 				// No local entry. R2 is preserved.
 			case 1:
-				// These require R2 be saved and restored by the caller. This isn't supported today.
+				// This is kind of a hack, but pass the hint about this symbol's
-				return errorf("%s: unable to handle local entry type 1", sb.Name())
+				// usage of R2 (R2 is a caller-save register not a TOC pointer, and
+				// this function does not have a distinct local entry) by setting
+				// its SymLocalentry to 1.
+				l.SetSymLocalentry(s, 1)
 			case 7:
 				return errorf("%s: invalid sym.other 0x%x", sb.Name(), elfsym.other)
 			default:
+				// Convert the word sized offset into bytes.
 				l.SetSymLocalentry(s, 4<<uint(flag-2))
 			}
 		}
@@ -1061,6 +1065,7 @@ func relSize(arch *sys.Arch, pn string, elftype uint32) (uint8, uint8, error) {
 		I386 | uint32(elf.R_386_GOTPC)<<16,
 		I386 | uint32(elf.R_386_GOT32X)<<16,
 		PPC64 | uint32(elf.R_PPC64_REL24)<<16,
+		PPC64 | uint32(elf.R_PPC64_REL24_NOTOC)<<16,
 		PPC64 | uint32(elf.R_PPC_REL32)<<16,
 		S390X | uint32(elf.R_390_32)<<16,
 		S390X | uint32(elf.R_390_PC32)<<16,
@@ -1077,6 +1082,9 @@ func relSize(arch *sys.Arch, pn string, elftype uint32) (uint8, uint8, error) {
 		ARM64 | uint32(elf.R_AARCH64_ABS64)<<16,
 		ARM64 | uint32(elf.R_AARCH64_PREL64)<<16,
 		PPC64 | uint32(elf.R_PPC64_ADDR64)<<16,
+		PPC64 | uint32(elf.R_PPC64_PCREL34)<<16,
+		PPC64 | uint32(elf.R_PPC64_GOT_PCREL34)<<16,
+		PPC64 | uint32(elf.R_PPC64_PLT_PCREL34_NOTOC)<<16,
 		S390X | uint32(elf.R_390_GLOB_DAT)<<16,
 		S390X | uint32(elf.R_390_RELATIVE)<<16,
 		S390X | uint32(elf.R_390_GOTOFF)<<16,

src/cmd/link/internal/loader/loader.go

@@ -1582,6 +1582,9 @@ func (l *Loader) SetSymPkg(i Sym, pkg string) {
 }
 
 // SymLocalentry returns an offset in bytes of the "local entry" of a symbol.
+//
+// On PPC64, a value of 1 indicates the symbol does not use or preserve a TOC
+// pointer in R2, nor does it have a distinct local entry.
 func (l *Loader) SymLocalentry(i Sym) uint8 {
 	return l.localentry[i]
 }

src/cmd/link/internal/ppc64/asm.go

@@ -189,7 +189,11 @@ func genstubs(ctxt *ld.Link, ldr *loader.Loader) {
 
 					// Turn this reloc into an R_CALLPOWER, and convert the TOC restore into a nop.
 					su.SetRelocType(i, objabi.R_CALLPOWER)
-					su.SetRelocAdd(i, r.Add()+int64(ldr.SymLocalentry(r.Sym())))
+					localEoffset := int64(ldr.SymLocalentry(r.Sym()))
+					if localEoffset == 1 {
+						ldr.Errorf(s, "Unsupported NOTOC call to %s", ldr.SymName(r.Sym()))
+					}
+					su.SetRelocAdd(i, r.Add()+localEoffset)
 					r.SetSiz(4)
 					rewritetonop(&ctxt.Target, ldr, su, int64(r.Off()+4), 0xFFFFFFFF, OP_TOCRESTORE)
 				}
@@ -435,7 +439,11 @@ func addelfdynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s lo
 		// callee. Hence, we need to go to the local entry
 		// point.  (If we don't do this, the callee will try
 		// to use r12 to compute r2.)
-		su.SetRelocAdd(rIdx, r.Add()+int64(ldr.SymLocalentry(targ)))
+		localEoffset := int64(ldr.SymLocalentry(targ))
+		if localEoffset == 1 {
+			ldr.Errorf(s, "Unsupported NOTOC call to %s", targ)
+		}
+		su.SetRelocAdd(rIdx, r.Add()+localEoffset)
 
 		if targType == sym.SDYNIMPORT {
 			// Should have been handled in elfsetupplt