[release-branch.go1.5] cmd/link: support new 386/amd64 relocations

The GNU binutils recently picked up support for new 386/amd64
relocations.  Add support for them in the Go linker when doing an
internal link.

The 386 relocation R_386_GOT32X was proposed in
https://groups.google.com/forum/#!topic/ia32-abi/GbJJskkid4I .  It can
be treated as identical to the R_386_GOT32 relocation.

The amd64 relocations R_X86_64_GOTPCRELX and R_X86_64_REX_GOTPCRELX were
proposed in
https://groups.google.com/forum/#!topic/x86-64-abi/n9AWHogmVY0 .  They
can both be treated as identical to the R_X86_64_GOTPCREL relocation.

The purpose of the new relocations is to permit additional linker
relaxations in some cases.  We do not attempt to support those cases.

While we're at it, remove the unused and in some cases out of date
_COUNT names from ld/elf.go.

Fixes #13114.

Change-Id: I34ef07f6fcd00cdd2996038ecf46bb77a49e968b
Reviewed-on: https://go-review.googlesource.com/16529
Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-on: https://go-review.googlesource.com/16982
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

Author: ianlancetaylor

src/cmd/link/internal/amd64/asm.go

@@ -141,7 +141,7 @@ func adddynrel(s *ld.LSym, r *ld.Reloc) {
 
 		return
 
-	case 256 + ld.R_X86_64_GOTPCREL:
+	case 256 + ld.R_X86_64_GOTPCREL, 256 + ld.R_X86_64_GOTPCRELX, 256 + ld.R_X86_64_REX_GOTPCRELX:
 		if targ.Type != obj.SDYNIMPORT {
 			// have symbol
 			if r.Off >= 2 && s.P[r.Off-2] == 0x8b {

src/cmd/link/internal/ld/elf.go

@@ -348,7 +348,23 @@ const (
 	R_X86_64_DTPOFF32          = 21
 	R_X86_64_GOTTPOFF          = 22
 	R_X86_64_TPOFF32           = 23
-	R_X86_64_COUNT             = 24
+	R_X86_64_PC64              = 24
+	R_X86_64_GOTOFF64          = 25
+	R_X86_64_GOTPC32           = 26
+	R_X86_64_GOT64             = 27
+	R_X86_64_GOTPCREL64        = 28
+	R_X86_64_GOTPC64           = 29
+	R_X86_64_GOTPLT64          = 30
+	R_X86_64_PLTOFF64          = 31
+	R_X86_64_SIZE32            = 32
+	R_X86_64_SIZE64            = 33
+	R_X86_64_GOTPC32_TLSDEC    = 34
+	R_X86_64_TLSDESC_CALL      = 35
+	R_X86_64_TLSDESC           = 36
+	R_X86_64_IRELATIVE         = 37
+	R_X86_64_PC32_BND          = 40
+	R_X86_64_GOTPCRELX         = 41
+	R_X86_64_REX_GOTPCRELX     = 42
 	R_AARCH64_ABS64            = 257
 	R_AARCH64_ABS32            = 258
 	R_AARCH64_CALL26           = 283
@@ -382,7 +398,6 @@ const (
 	R_ALPHA_GLOB_DAT           = 25
 	R_ALPHA_JMP_SLOT           = 26
 	R_ALPHA_RELATIVE           = 27
-	R_ALPHA_COUNT              = 28
 	R_ARM_NONE                 = 0
 	R_ARM_PC24                 = 1
 	R_ARM_ABS32                = 2
@@ -422,7 +437,6 @@ const (
 	R_ARM_RABS32               = 253
 	R_ARM_RPC24                = 254
 	R_ARM_RBASE                = 255
-	R_ARM_COUNT                = 38
 	R_386_NONE                 = 0
 	R_386_32                   = 1
 	R_386_PC32                 = 2
@@ -454,7 +468,11 @@ const (
 	R_386_TLS_DTPMOD32         = 35
 	R_386_TLS_DTPOFF32         = 36
 	R_386_TLS_TPOFF32          = 37
-	R_386_COUNT                = 38
+	R_386_TLS_GOTDESC          = 39
+	R_386_TLS_DESC_CALL        = 40
+	R_386_TLS_DESC             = 41
+	R_386_IRELATIVE            = 42
+	R_386_GOT32X               = 43
 	R_PPC_NONE                 = 0
 	R_PPC_ADDR32               = 1
 	R_PPC_ADDR24               = 2
@@ -492,7 +510,6 @@ const (
 	R_PPC_SECTOFF_LO           = 34
 	R_PPC_SECTOFF_HI           = 35
 	R_PPC_SECTOFF_HA           = 36
-	R_PPC_COUNT                = 37
 	R_PPC_TLS                  = 67
 	R_PPC_DTPMOD32             = 68
 	R_PPC_TPREL16              = 69
@@ -533,7 +550,6 @@ const (
 	R_PPC_EMB_RELST_HA         = 114
 	R_PPC_EMB_BIT_FLD          = 115
 	R_PPC_EMB_RELSDA           = 116
-	R_PPC_EMB_COUNT            = R_PPC_EMB_RELSDA - R_PPC_EMB_NADDR32 + 1
 	R_PPC64_REL24              = R_PPC_REL24
 	R_PPC64_JMP_SLOT           = R_PPC_JMP_SLOT
 	R_PPC64_ADDR64             = 38

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

@@ -1001,12 +1001,15 @@ func reltype(pn string, elftype int, siz *uint8) int {
 		'6' | R_X86_64_PC32<<24,
 		'6' | R_X86_64_PLT32<<24,
 		'6' | R_X86_64_GOTPCREL<<24,
+		'6' | R_X86_64_GOTPCRELX<<24,
+		'6' | R_X86_64_REX_GOTPCRELX<<24,
 		'8' | R_386_32<<24,
 		'8' | R_386_PC32<<24,
 		'8' | R_386_GOT32<<24,
 		'8' | R_386_PLT32<<24,
 		'8' | R_386_GOTOFF<<24,
 		'8' | R_386_GOTPC<<24,
+		'8' | R_386_GOT32X<<24,
 		'9' | R_PPC64_REL24<<24:
 		*siz = 4
 

src/cmd/link/internal/x86/asm.go

@@ -78,7 +78,7 @@ func adddynrel(s *ld.LSym, r *ld.Reloc) {
 
 		return
 
-	case 256 + ld.R_386_GOT32:
+	case 256 + ld.R_386_GOT32, 256 + ld.R_386_GOT32X:
 		if targ.Type != obj.SDYNIMPORT {
 			// have symbol
 			if r.Off >= 2 && s.P[r.Off-2] == 0x8b {