cmd/asm: align an instruction or a function's address
Recently, the gVisor project needs an instruction's address
with 128 bytes alignment and a function's start address with
2K bytes alignment to fit the architecture requirement for
interrupt table.
This patch allows aligning the address of an instruction to be
aligned to a specific value (2^n and not higher than 2048) and
the address of a function to be 2048 bytes.
The main changes include:
1. Adds ALIGN2048 flag to align a function's address with
2048 bytes.
e.g. "TEXT ·Add(SB),NOSPLIT|ALIGN2048" indicates that the
address of Add function should be aligned to 2048 bytes.
2. Adds a new element in the FuncInfo structure defined in
cmd/internal/obj/link.go file to record the alignment
information.
3. Adds a new element in the Func structure defined in
cmd/internal/goobj/read.go file to read the alignment
information.
4. Because go introduces a new object file format, also add
a new element in the FuncInfo structure defined in
cmd/internal/goobj2/funcinfo.go to record the alignment
information.
5. Adds the assembler support to align an intruction's offset
with a specific value (2^n and not higher than 2048).
e.g. "PCALIGN $256" indicates that the next instruction should
be aligned to 256 bytes.
This CL also adds a test.
Change-Id: I31cfa6fb5bc35dee2c44bf65913e90cddfcb492a
Reviewed-on: https://go-review.googlesource.com/c/go/+/212767
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/cmd/internal/goobj/read.go b/src/cmd/internal/goobj/read.go
index e61e95d..48537d2 100644
--- a/src/cmd/internal/goobj/read.go
+++ b/src/cmd/internal/goobj/read.go
@@ -95,6 +95,7 @@
type Func struct {
Args int64 // size in bytes of argument frame: inputs and outputs
Frame int64 // size in bytes of local variable frame
+ Align uint32 // alignment requirement in bytes for the address of the function
Leaf bool // function omits save of link register (ARM)
NoSplit bool // function omits stack split prologue
TopFrame bool // function is the top of the call stack
@@ -590,6 +591,7 @@
s.Func = f
f.Args = r.readInt()
f.Frame = r.readInt()
+ f.Align = uint32(r.readInt())
flags := r.readInt()
f.Leaf = flags&(1<<0) != 0
f.TopFrame = flags&(1<<4) != 0
diff --git a/src/cmd/internal/goobj/readnew.go b/src/cmd/internal/goobj/readnew.go
index 3f9d0d1..1acf18a 100644
--- a/src/cmd/internal/goobj/readnew.go
+++ b/src/cmd/internal/goobj/readnew.go
@@ -149,6 +149,7 @@
f := &Func{
Args: int64(info.Args),
Frame: int64(info.Locals),
+ Align: info.Align,
NoSplit: info.NoSplit != 0,
Leaf: osym.Leaf(),
TopFrame: osym.TopFrame(),
diff --git a/src/cmd/internal/goobj2/funcinfo.go b/src/cmd/internal/goobj2/funcinfo.go
index 8620931..946415b 100644
--- a/src/cmd/internal/goobj2/funcinfo.go
+++ b/src/cmd/internal/goobj2/funcinfo.go
@@ -18,6 +18,7 @@
Args uint32
Locals uint32
+ Align uint32
Pcsp uint32
Pcfile uint32
@@ -42,6 +43,7 @@
writeUint32(a.Args)
writeUint32(a.Locals)
+ writeUint32(a.Align)
writeUint32(a.Pcsp)
writeUint32(a.Pcfile)
@@ -79,6 +81,7 @@
a.Args = readUint32()
a.Locals = readUint32()
+ a.Align = readUint32()
a.Pcsp = readUint32()
a.Pcfile = readUint32()
diff --git a/src/cmd/internal/obj/arm64/asm7.go b/src/cmd/internal/obj/arm64/asm7.go
index e8b092a..dbe816e 100644
--- a/src/cmd/internal/obj/arm64/asm7.go
+++ b/src/cmd/internal/obj/arm64/asm7.go
@@ -886,25 +886,10 @@
// align code to a certain length by padding bytes.
func pcAlignPadLength(pc int64, alignedValue int64, ctxt *obj.Link) int {
- switch alignedValue {
- case 8:
- if pc%8 == 4 {
- return 4
- }
- case 16:
- switch pc % 16 {
- case 4:
- return 12
- case 8:
- return 8
- case 12:
- return 4
- }
- default:
- ctxt.Diag("Unexpected alignment: %d for PCALIGN directive\n", alignedValue)
+ if !((alignedValue&(alignedValue-1) == 0) && 8 <= alignedValue && alignedValue <= 2048) {
+ ctxt.Diag("alignment value of an instruction must be a power of two and in the range [8, 2048], got %d\n", alignedValue)
}
-
- return 0
+ return int(-pc & (alignedValue - 1))
}
func span7(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
@@ -940,8 +925,12 @@
if m == 0 {
switch p.As {
case obj.APCALIGN:
- a := p.From.Offset
- m = pcAlignPadLength(pc, a, ctxt)
+ alignedValue := p.From.Offset
+ m = pcAlignPadLength(pc, alignedValue, ctxt)
+ // Update the current text symbol ailgnment value.
+ if int32(alignedValue) > cursym.Func.Align {
+ cursym.Func.Align = int32(alignedValue)
+ }
break
case obj.ANOP, obj.AFUNCDATA, obj.APCDATA:
continue
@@ -1017,8 +1006,8 @@
if m == 0 {
switch p.As {
case obj.APCALIGN:
- a := p.From.Offset
- m = pcAlignPadLength(pc, a, ctxt)
+ alignedValue := p.From.Offset
+ m = pcAlignPadLength(pc, alignedValue, ctxt)
break
case obj.ANOP, obj.AFUNCDATA, obj.APCDATA:
continue
diff --git a/src/cmd/internal/obj/arm64/asm_test.go b/src/cmd/internal/obj/arm64/asm_test.go
index 1691828..9efdb02 100644
--- a/src/cmd/internal/obj/arm64/asm_test.go
+++ b/src/cmd/internal/obj/arm64/asm_test.go
@@ -18,7 +18,9 @@
// TestLarge generates a very large file to verify that large
// program builds successfully, in particular, too-far
-// conditional branches are fixed.
+// conditional branches are fixed, and also verify that the
+// instruction's pc can be correctly aligned even when branches
+// need to be fixed.
func TestLarge(t *testing.T) {
if testing.Short() {
t.Skip("Skip in short mode")
@@ -41,11 +43,28 @@
t.Fatalf("can't write output: %v\n", err)
}
- // build generated file
- cmd := exec.Command(testenv.GoToolPath(t), "tool", "asm", "-o", filepath.Join(dir, "x.o"), tmpfile)
+ pattern := `0x0080\s00128\s\(.*\)\tMOVD\t\$3,\sR3`
+
+ // assemble generated file
+ cmd := exec.Command(testenv.GoToolPath(t), "tool", "asm", "-S", "-o", filepath.Join(dir, "test.o"), tmpfile)
cmd.Env = append(os.Environ(), "GOARCH=arm64", "GOOS=linux")
out, err := cmd.CombinedOutput()
if err != nil {
+ t.Errorf("Assemble failed: %v, output: %s", err, out)
+ }
+ matched, err := regexp.MatchString(pattern, string(out))
+ if err != nil {
+ t.Fatal(err)
+ }
+ if !matched {
+ t.Errorf("The alignment is not correct: %t, output:%s\n", matched, out)
+ }
+
+ // build generated file
+ cmd = exec.Command(testenv.GoToolPath(t), "tool", "asm", "-o", filepath.Join(dir, "x.o"), tmpfile)
+ cmd.Env = append(os.Environ(), "GOARCH=arm64", "GOOS=linux")
+ out, err = cmd.CombinedOutput()
+ if err != nil {
t.Errorf("Build failed: %v, output: %s", err, out)
}
}
@@ -56,6 +75,8 @@
fmt.Fprintln(buf, "TBZ $5, R0, label")
fmt.Fprintln(buf, "CBZ R0, label")
fmt.Fprintln(buf, "BEQ label")
+ fmt.Fprintln(buf, "PCALIGN $128")
+ fmt.Fprintln(buf, "MOVD $3, R3")
for i := 0; i < 1<<19; i++ {
fmt.Fprintln(buf, "MOVD R0, R1")
}
diff --git a/src/cmd/internal/obj/link.go b/src/cmd/internal/obj/link.go
index d1cc536..0879c61 100644
--- a/src/cmd/internal/obj/link.go
+++ b/src/cmd/internal/obj/link.go
@@ -398,6 +398,7 @@
type FuncInfo struct {
Args int32
Locals int32
+ Align int32
Text *Prog
Autot map[*LSym]struct{}
Pcln Pcln
diff --git a/src/cmd/internal/obj/objfile.go b/src/cmd/internal/obj/objfile.go
index 7fd97f7..46e8a55 100644
--- a/src/cmd/internal/obj/objfile.go
+++ b/src/cmd/internal/obj/objfile.go
@@ -346,6 +346,7 @@
w.writeInt(int64(s.Func.Args))
w.writeInt(int64(s.Func.Locals))
+ w.writeInt(int64(s.Func.Align))
w.writeBool(s.NoSplit())
flags = int64(0)
if s.Leaf() {
diff --git a/src/cmd/internal/obj/objfile2.go b/src/cmd/internal/obj/objfile2.go
index 69019e0..626df56 100644
--- a/src/cmd/internal/obj/objfile2.go
+++ b/src/cmd/internal/obj/objfile2.go
@@ -374,6 +374,7 @@
NoSplit: nosplit,
Args: uint32(s.Func.Args),
Locals: uint32(s.Func.Locals),
+ Align: uint32(s.Func.Align),
}
pc := &s.Func.Pcln
o.Pcsp = pcdataoff
diff --git a/src/cmd/internal/obj/plist.go b/src/cmd/internal/obj/plist.go
index 7579dd0..be19221 100644
--- a/src/cmd/internal/obj/plist.go
+++ b/src/cmd/internal/obj/plist.go
@@ -133,6 +133,13 @@
s.Set(AttrNeedCtxt, flag&NEEDCTXT != 0)
s.Set(AttrNoFrame, flag&NOFRAME != 0)
s.Set(AttrTopFrame, flag&TOPFRAME != 0)
+ if flag&ALIGN2048 != 0 {
+ if objabi.GOARCH != "arm64" {
+ ctxt.Diag("ALIGN2048 flag only works on ARM64 at present.")
+ }
+ s.Func.Align = 2048
+ }
+
s.Type = objabi.STEXT
ctxt.Text = append(ctxt.Text, s)
diff --git a/src/cmd/internal/obj/textflag.go b/src/cmd/internal/obj/textflag.go
index d2cec73..3681a3b6 100644
--- a/src/cmd/internal/obj/textflag.go
+++ b/src/cmd/internal/obj/textflag.go
@@ -51,4 +51,9 @@
// Function is the top of the call stack. Call stack unwinders should stop
// at this function.
TOPFRAME = 2048
+
+ // ALIGN2048 means that the address of the function must be aligned to a
+ // 2048 bytes boundary.
+ // Only works on arm64 at present.
+ ALIGN2048 = 4096
)
diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index 7ca01c8..31613e5 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -2119,6 +2119,10 @@
funcsize = uint64(s.Size)
}
+ if sect.Align < s.Align {
+ sect.Align = s.Align
+ }
+
// On ppc64x a text section should not be larger than 2^26 bytes due to the size of
// call target offset field in the bl instruction. Splitting into smaller text
// sections smaller than this limit allows the GNU linker to modify the long calls
diff --git a/src/cmd/link/internal/loader/loader.go b/src/cmd/link/internal/loader/loader.go
index 0adc395..bd9c6b4 100644
--- a/src/cmd/link/internal/loader/loader.go
+++ b/src/cmd/link/internal/loader/loader.go
@@ -1227,6 +1227,7 @@
info.Pcdata = append(info.Pcdata, info.PcdataEnd) // for the ease of knowing where it ends
pc.Args = int32(info.Args)
pc.Locals = int32(info.Locals)
+ s.Align = int32(info.Align)
npc := len(info.Pcdata) - 1 // -1 as we appended one above
pc.Pcdata = pcDataBatch[:npc:npc]
diff --git a/src/cmd/link/internal/objfile/objfile.go b/src/cmd/link/internal/objfile/objfile.go
index a15d3c3..295acb2 100644
--- a/src/cmd/link/internal/objfile/objfile.go
+++ b/src/cmd/link/internal/objfile/objfile.go
@@ -312,6 +312,7 @@
pc.Args = r.readInt32()
pc.Locals = r.readInt32()
+ s.Align = r.readInt32()
if r.readUint8() != 0 {
s.Attr |= sym.AttrNoSplit
}
diff --git a/src/cmd/link/link_test.go b/src/cmd/link/link_test.go
index 4f792bd..025e882 100644
--- a/src/cmd/link/link_test.go
+++ b/src/cmd/link/link_test.go
@@ -3,6 +3,7 @@
import (
"bufio"
"bytes"
+ "cmd/internal/objabi"
"debug/macho"
"internal/testenv"
"io/ioutil"
@@ -447,3 +448,103 @@
t.Errorf("unexpected output:\n%s", out)
}
}
+
+const testFuncAlignSrc = `
+package main
+import (
+ "fmt"
+ "reflect"
+)
+func alignFunc()
+func alignPc()
+
+func main() {
+ addr1 := reflect.ValueOf(alignFunc).Pointer()
+ addr2 := reflect.ValueOf(alignPc).Pointer()
+ switch {
+ case (addr1 % 2048) != 0 && (addr2 % 512) != 0:
+ fmt.Printf("expected 2048 bytes alignment, got %v; expected 512 bytes alignment, got %v\n", addr1, addr2)
+ case (addr2 % 512) != 0:
+ fmt.Printf("expected 512 bytes alignment, got %v\n", addr2)
+ case (addr1 % 2048) != 0:
+ fmt.Printf("expected 2048 bytes alignment, got %v\n", addr1)
+ default:
+ fmt.Printf("PASS")
+ }
+}
+`
+
+const testFuncAlignAsmSrc = `
+#include "textflag.h"
+TEXT ·alignFunc(SB),NOSPLIT|ALIGN2048, $0-0
+ MOVD $1, R0
+ MOVD $2, R1
+ RET
+
+TEXT ·alignPc(SB),NOSPLIT, $0-0
+ MOVD $2, R0
+ PCALIGN $512
+ MOVD $3, R1
+ RET
+`
+
+// TestFuncAlign verifies that the address of a function can be aligned
+// with a specfic value on arm64.
+func TestFuncAlign(t *testing.T) {
+ if objabi.GOARCH != "arm64" {
+ t.Skipf("Skipping FuncAlign test on %s", objabi.GOARCH)
+ }
+ testenv.MustHaveGoBuild(t)
+
+ tmpdir, err := ioutil.TempDir("", "TestFuncAlign")
+ if err != nil {
+ t.Fatal(err)
+ }
+ defer os.RemoveAll(tmpdir)
+
+ src := filepath.Join(tmpdir, "falign.go")
+ err = ioutil.WriteFile(src, []byte(testFuncAlignSrc), 0666)
+ if err != nil {
+ t.Fatal(err)
+ }
+ src = filepath.Join(tmpdir, "falign.s")
+ err = ioutil.WriteFile(src, []byte(testFuncAlignAsmSrc), 0666)
+ if err != nil {
+ t.Fatal(err)
+ }
+
+ // Build and run with old object file format.
+ cmd := exec.Command(testenv.GoToolPath(t), "build", "-o", "falign")
+ cmd.Env = append(os.Environ(), "GOARCH=arm64", "GOOS=linux")
+ cmd.Dir = tmpdir
+ out, err := cmd.CombinedOutput()
+ if err != nil {
+ t.Errorf("build failed: %v", err)
+ }
+ cmd = exec.Command(tmpdir + "/falign")
+ out, err = cmd.CombinedOutput()
+ if err != nil {
+ t.Errorf("failed to run with err %v, output: %s", err, out)
+ }
+ if string(out) != "PASS" {
+ t.Errorf("unexpected output: %s\n", out)
+ }
+
+ // Build and run with new object file format.
+ cmd = exec.Command(testenv.GoToolPath(t), "build", "-o", "falign", "-gcflags=all=-newobj", "-asmflags=all=-newobj", "-ldflags=-newobj")
+ cmd.Env = append(os.Environ(), "GOARCH=arm64", "GOOS=linux")
+ cmd.Dir = tmpdir
+ out, err = cmd.CombinedOutput()
+ if err != nil {
+ t.Errorf("build with newobj failed: %v", err)
+ }
+ cmd = exec.Command(tmpdir + "/falign")
+ out, err = cmd.CombinedOutput()
+ if err != nil {
+ t.Errorf("failed to run with -newobj, err: %v, output: %s", err, out)
+ }
+ if string(out) != "PASS" {
+ t.Errorf("unexpected output with -newobj: %s\n", out)
+ }
+
+}
diff --git a/src/runtime/textflag.h b/src/runtime/textflag.h
index daca36d..bbbef63 100644
--- a/src/runtime/textflag.h
+++ b/src/runtime/textflag.h
@@ -35,3 +35,8 @@
// Function is the top of the call stack. Call stack unwinders should stop
// at this function.
#define TOPFRAME 2048
+// ALIGN2048 means that the address of the function must be aligned to a
+// 2048 bytes boundary.
+// Only works on arm64 at present.
+#define ALIGN2048 4096
+
