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cmd/link: use TOC-relative trampolines on PPC64 when needed
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When linking a PIE binary with the internal linker, TOC relative
relocations need to be generated. Update trampolines to indirect
call using R12 to more closely match the AIX/ELFv2 regardless of
buildmode, and work with position-indepdent code.

Likewise, update the check for offseting R_CALLPOWER relocs to
make a local call. It should be checking ldr.AttrExternal, not
ldr.IsExternal. This offset should not be adjusted for external
(non-go) object files, it is handled when ELF reloc are translated
into go relocs.

And, update trampoline tests to verify these are generated correctly
and produce a working binary using -buildmode=pie on ppc64le.

Fixes #52337

Change-Id: I8a2dea06c3237bdf0e87888b56a17b6c4c99a7de
Reviewed-on: https://go-review.googlesource.com/c/go/+/400234
Reviewed-by: Than McIntosh <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Run-TryBot: Paul Murphy <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
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@pmur
pmur committed Apr 19, 2022
1 parent e8d9fd7 commit caa4631
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Showing 2 changed files with 78 additions and 71 deletions.
51 changes: 23 additions & 28 deletions src/cmd/link/internal/ppc64/asm.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -766,7 +766,7 @@ func trampoline(ctxt *ld.Link, ldr *loader.Loader, ri int, rs, s loader.Sym) {
// For external linking, the linker can insert a call stub to handle a long call, but depends on having the TOC address in
// r2. For those build modes with external linking where the TOC address is not maintained in r2, trampolines must be created.
if ctxt.IsExternal() && r2Valid(ctxt) {
// No trampolines needed since r2 contains the TOC
// The TOC pointer is valid. The external linker will insert trampolines.
return
}

Expand Down Expand Up @@ -819,14 +819,9 @@ func trampoline(ctxt *ld.Link, ldr *loader.Loader, ri int, rs, s loader.Sym) {
}
}
if ldr.SymType(tramp) == 0 {
if r2Valid(ctxt) {
// Should have returned for above cases
ctxt.Errorf(s, "unexpected trampoline for shared or dynamic linking")
} else {
trampb := ldr.MakeSymbolUpdater(tramp)
ctxt.AddTramp(trampb)
gentramp(ctxt, ldr, trampb, rs, r.Add())
}
trampb := ldr.MakeSymbolUpdater(tramp)
ctxt.AddTramp(trampb)
gentramp(ctxt, ldr, trampb, rs, r.Add())
}
sb := ldr.MakeSymbolUpdater(s)
relocs := sb.Relocs()
Expand All @@ -842,7 +837,6 @@ func trampoline(ctxt *ld.Link, ldr *loader.Loader, ri int, rs, s loader.Sym) {
func gentramp(ctxt *ld.Link, ldr *loader.Loader, tramp *loader.SymbolBuilder, target loader.Sym, offset int64) {
tramp.SetSize(16) // 4 instructions
P := make([]byte, tramp.Size())
t := ldr.SymValue(target) + offset
var o1, o2 uint32

if ctxt.IsAIX() {
Expand All @@ -851,8 +845,8 @@ func gentramp(ctxt *ld.Link, ldr *loader.Loader, tramp *loader.SymbolBuilder, ta
// However, all text symbols are accessed with a TOC symbol as
// text relocations aren't supposed to be possible.
// So, keep using the external linking way to be more AIX friendly.
o1 = uint32(0x3fe20000) // lis r2, toctargetaddr hi
o2 = uint32(0xebff0000) // ld r31, toctargetaddr lo
o1 = uint32(0x3c000000) | 12<<21 | 2<<16 // addis r12, r2, toctargetaddr hi
o2 = uint32(0xe8000000) | 12<<21 | 12<<16 // ld r12, r12, toctargetaddr lo

toctramp := ldr.CreateSymForUpdate("TOC."+ldr.SymName(tramp.Sym()), 0)
toctramp.SetType(sym.SXCOFFTOC)
Expand All @@ -866,31 +860,32 @@ func gentramp(ctxt *ld.Link, ldr *loader.Loader, tramp *loader.SymbolBuilder, ta
// Used for default build mode for an executable
// Address of the call target is generated using
// relocation and doesn't depend on r2 (TOC).
o1 = uint32(0x3fe00000) // lis r31,targetaddr hi
o2 = uint32(0x3bff0000) // addi r31,targetaddr lo
o1 = uint32(0x3c000000) | 12<<21 // lis r12,targetaddr hi
o2 = uint32(0x38000000) | 12<<21 | 12<<16 // addi r12,r12,targetaddr lo

// With external linking, the target address must be
// relocated using LO and HA
if ctxt.IsExternal() || ldr.SymValue(target) == 0 {
t := ldr.SymValue(target)
if t == 0 || r2Valid(ctxt) || ctxt.IsExternal() {
// Target address is unknown, generate relocations
r, _ := tramp.AddRel(objabi.R_ADDRPOWER)
if r2Valid(ctxt) {
// Use a TOC relative address if R2 holds the TOC pointer
o1 |= uint32(2 << 16) // Transform lis r31,ha into addis r31,r2,ha
r.SetType(objabi.R_ADDRPOWER_TOCREL)
}
r.SetOff(0)
r.SetSiz(8) // generates 2 relocations: HA + LO
r.SetSym(target)
r.SetAdd(offset)
} else {
// adjustment needed if lo has sign bit set
// when using addi to compute address
val := uint32((t & 0xffff0000) >> 16)
if t&0x8000 != 0 {
val += 1
}
o1 |= val // hi part of addr
o2 |= uint32(t & 0xffff) // lo part of addr
// The target address is known, resolve it
t += offset
o1 |= (uint32(t) + 0x8000) >> 16 // HA
o2 |= uint32(t) & 0xFFFF // LO
}
}

o3 := uint32(0x7fe903a6) // mtctr r31
o4 := uint32(0x4e800420) // bctr
o3 := uint32(0x7c0903a6) | 12<<21 // mtctr r12
o4 := uint32(0x4e800420) // bctr
ctxt.Arch.ByteOrder.PutUint32(P, o1)
ctxt.Arch.ByteOrder.PutUint32(P[4:], o2)
ctxt.Arch.ByteOrder.PutUint32(P[8:], o3)
Expand Down Expand Up @@ -962,7 +957,7 @@ func archreloc(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, r loade
// If we are linking PIE or shared code, all golang generated object files have an extra 2 instruction prologue
// to regenerate the TOC pointer from R12. The exception are two special case functions tested below. Note,
// local call offsets for externally generated objects are accounted for when converting into golang relocs.
if !ldr.IsExternal(rs) && ldr.AttrShared(rs) && tgtName != "runtime.duffzero" && tgtName != "runtime.duffcopy" {
if !ldr.AttrExternal(rs) && ldr.AttrShared(rs) && tgtName != "runtime.duffzero" && tgtName != "runtime.duffcopy" {
// Furthermore, only apply the offset if the target looks like the start of a function call.
if r.Add() == 0 && ldr.SymType(rs) == sym.STEXT {
t += 8
Expand Down
98 changes: 55 additions & 43 deletions src/cmd/link/link_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -642,8 +642,12 @@ func TestTrampoline(t *testing.T) {
// For stress test, we set -debugtramp=2 flag, which sets a very low
// threshold for trampoline generation, and essentially all cross-package
// calls will use trampolines.
buildmodes := []string{"default"}
switch runtime.GOARCH {
case "arm", "arm64", "ppc64", "ppc64le":
case "arm", "arm64", "ppc64":
case "ppc64le":
// Trampolines are generated differently when internal linking PIE, test them too.
buildmodes = append(buildmodes, "pie")
default:
t.Skipf("trampoline insertion is not implemented on %s", runtime.GOARCH)
}
Expand All @@ -661,18 +665,20 @@ func TestTrampoline(t *testing.T) {
}
exe := filepath.Join(tmpdir, "hello.exe")

cmd := exec.Command(testenv.GoToolPath(t), "build", "-ldflags=-debugtramp=2", "-o", exe, src)
out, err := cmd.CombinedOutput()
if err != nil {
t.Fatalf("build failed: %v\n%s", err, out)
}
cmd = exec.Command(exe)
out, err = cmd.CombinedOutput()
if err != nil {
t.Errorf("executable failed to run: %v\n%s", err, out)
}
if string(out) != "hello\n" {
t.Errorf("unexpected output:\n%s", out)
for _, mode := range buildmodes {
cmd := exec.Command(testenv.GoToolPath(t), "build", "-buildmode="+mode, "-ldflags=-debugtramp=2", "-o", exe, src)
out, err := cmd.CombinedOutput()
if err != nil {
t.Fatalf("build (%s) failed: %v\n%s", mode, err, out)
}
cmd = exec.Command(exe)
out, err = cmd.CombinedOutput()
if err != nil {
t.Errorf("executable failed to run (%s): %v\n%s", mode, err, out)
}
if string(out) != "hello\n" {
t.Errorf("unexpected output (%s):\n%s", mode, out)
}
}
}

Expand All @@ -693,8 +699,12 @@ func TestTrampolineCgo(t *testing.T) {
// For stress test, we set -debugtramp=2 flag, which sets a very low
// threshold for trampoline generation, and essentially all cross-package
// calls will use trampolines.
buildmodes := []string{"default"}
switch runtime.GOARCH {
case "arm", "arm64", "ppc64", "ppc64le":
case "arm", "arm64", "ppc64":
case "ppc64le":
// Trampolines are generated differently when internal linking PIE, test them too.
buildmodes = append(buildmodes, "pie")
default:
t.Skipf("trampoline insertion is not implemented on %s", runtime.GOARCH)
}
Expand All @@ -713,37 +723,39 @@ func TestTrampolineCgo(t *testing.T) {
}
exe := filepath.Join(tmpdir, "hello.exe")

cmd := exec.Command(testenv.GoToolPath(t), "build", "-ldflags=-debugtramp=2", "-o", exe, src)
out, err := cmd.CombinedOutput()
if err != nil {
t.Fatalf("build failed: %v\n%s", err, out)
}
cmd = exec.Command(exe)
out, err = cmd.CombinedOutput()
if err != nil {
t.Errorf("executable failed to run: %v\n%s", err, out)
}
if string(out) != "hello\n" && string(out) != "hello\r\n" {
t.Errorf("unexpected output:\n%s", out)
}
for _, mode := range buildmodes {
cmd := exec.Command(testenv.GoToolPath(t), "build", "-buildmode="+mode, "-ldflags=-debugtramp=2", "-o", exe, src)
out, err := cmd.CombinedOutput()
if err != nil {
t.Fatalf("build (%s) failed: %v\n%s", mode, err, out)
}
cmd = exec.Command(exe)
out, err = cmd.CombinedOutput()
if err != nil {
t.Errorf("executable failed to run (%s): %v\n%s", mode, err, out)
}
if string(out) != "hello\n" && string(out) != "hello\r\n" {
t.Errorf("unexpected output (%s):\n%s", mode, out)
}

// Test internal linking mode.
// Test internal linking mode.

if runtime.GOARCH == "ppc64" || runtime.GOARCH == "ppc64le" || (runtime.GOARCH == "arm64" && runtime.GOOS == "windows") || !testenv.CanInternalLink() {
return // internal linking cgo is not supported
}
cmd = exec.Command(testenv.GoToolPath(t), "build", "-ldflags=-debugtramp=2 -linkmode=internal", "-o", exe, src)
out, err = cmd.CombinedOutput()
if err != nil {
t.Fatalf("build failed: %v\n%s", err, out)
}
cmd = exec.Command(exe)
out, err = cmd.CombinedOutput()
if err != nil {
t.Errorf("executable failed to run: %v\n%s", err, out)
}
if string(out) != "hello\n" && string(out) != "hello\r\n" {
t.Errorf("unexpected output:\n%s", out)
if runtime.GOARCH == "ppc64" || (runtime.GOARCH == "arm64" && runtime.GOOS == "windows") || !testenv.CanInternalLink() {
return // internal linking cgo is not supported
}
cmd = exec.Command(testenv.GoToolPath(t), "build", "-buildmode="+mode, "-ldflags=-debugtramp=2 -linkmode=internal", "-o", exe, src)
out, err = cmd.CombinedOutput()
if err != nil {
t.Fatalf("build (%s) failed: %v\n%s", mode, err, out)
}
cmd = exec.Command(exe)
out, err = cmd.CombinedOutput()
if err != nil {
t.Errorf("executable failed to run (%s): %v\n%s", mode, err, out)
}
if string(out) != "hello\n" && string(out) != "hello\r\n" {
t.Errorf("unexpected output (%s):\n%s", mode, out)
}
}
}

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