cmd/link: put padding between functions, not at the end of a function
Functions should be declared to end after the last real instruction, not
after the last padding byte. We achieve this by adding the padding while
assembling the text section in the linker instead of adding the padding
to the function symbol in the compiler. This change makes dtrace happy.
TODO: check that this works with external linking
Fixes #15969
Change-Id: I973e478d0cd34b61be1ddc55410552cbd645ad62
Reviewed-on: https://go-review.googlesource.com/24040
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/cmd/internal/obj/x86/asm6.go b/src/cmd/internal/obj/x86/asm6.go
index 414a4d3..676da40 100644
--- a/src/cmd/internal/obj/x86/asm6.go
+++ b/src/cmd/internal/obj/x86/asm6.go
@@ -1986,16 +1986,6 @@
c = naclpad(ctxt, s, c, -c&31)
}
- // Pad functions with trap instruction, to catch invalid jumps
- if c&(FuncAlign-1) != 0 {
- v := -c & (FuncAlign - 1)
- s.Grow(int64(c) + int64(v))
- for i := c; i < c+v; i++ {
- // 0xCC is INT $3 - breakpoint instruction
- s.P[i] = uint8(0xCC)
- }
- c += v
- }
s.Size = int64(c)
if false { /* debug['a'] > 1 */
diff --git a/src/cmd/link/internal/amd64/asm.go b/src/cmd/link/internal/amd64/asm.go
index 48250c9..eff9a22 100644
--- a/src/cmd/link/internal/amd64/asm.go
+++ b/src/cmd/link/internal/amd64/asm.go
@@ -615,7 +615,8 @@
sect := ld.Segtext.Sect
ld.Cseek(int64(sect.Vaddr - ld.Segtext.Vaddr + ld.Segtext.Fileoff))
- ld.Codeblk(int64(sect.Vaddr), int64(sect.Length))
+ // 0xCC is INT $3 - breakpoint instruction
+ ld.CodeblkPad(int64(sect.Vaddr), int64(sect.Length), []byte{0xCC})
for sect = sect.Next; sect != nil; sect = sect.Next {
ld.Cseek(int64(sect.Vaddr - ld.Segtext.Vaddr + ld.Segtext.Fileoff))
ld.Datblk(int64(sect.Vaddr), int64(sect.Length))
diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index 6e326ec..57a0dad 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -790,11 +790,14 @@
}
func Codeblk(addr int64, size int64) {
+ CodeblkPad(addr, size, zeros[:])
+}
+func CodeblkPad(addr int64, size int64, pad []byte) {
if Debug['a'] != 0 {
fmt.Fprintf(Bso, "codeblk [%#x,%#x) at offset %#x\n", addr, addr+size, Cpos())
}
- blkSlice(Ctxt.Textp, addr, size)
+ blkSlice(Ctxt.Textp, addr, size, pad)
/* again for printing */
if Debug['a'] == 0 {
@@ -858,7 +861,7 @@
// blkSlice is a variant of blk that processes slices.
// After text symbols are converted from a linked list to a slice,
// delete blk and give this function its name.
-func blkSlice(syms []*LSym, addr, size int64) {
+func blkSlice(syms []*LSym, addr, size int64, pad []byte) {
for i, s := range syms {
if s.Type&obj.SSUB == 0 && s.Value >= addr {
syms = syms[i:]
@@ -880,13 +883,13 @@
errorexit()
}
if addr < s.Value {
- strnput("", int(s.Value-addr))
+ strnputPad("", int(s.Value-addr), pad)
addr = s.Value
}
Cwrite(s.P)
addr += int64(len(s.P))
if addr < s.Value+s.Size {
- strnput("", int(s.Value+s.Size-addr))
+ strnputPad("", int(s.Value+s.Size-addr), pad)
addr = s.Value + s.Size
}
if addr != s.Value+s.Size {
@@ -899,7 +902,7 @@
}
if addr < eaddr {
- strnput("", int(eaddr-addr))
+ strnputPad("", int(eaddr-addr), pad)
}
Cflush()
}
@@ -909,7 +912,7 @@
fmt.Fprintf(Bso, "datblk [%#x,%#x) at offset %#x\n", addr, addr+size, Cpos())
}
- blkSlice(datap, addr, size)
+ blkSlice(datap, addr, size, zeros[:])
/* again for printing */
if Debug['a'] == 0 {
@@ -986,23 +989,27 @@
var zeros [512]byte
// strnput writes the first n bytes of s.
-// If n is larger then len(s),
+// If n is larger than len(s),
// it is padded with NUL bytes.
func strnput(s string, n int) {
+ strnputPad(s, n, zeros[:])
+}
+
+// strnput writes the first n bytes of s.
+// If n is larger than len(s),
+// it is padded with the bytes in pad (repeated as needed).
+func strnputPad(s string, n int, pad []byte) {
if len(s) >= n {
Cwritestring(s[:n])
} else {
Cwritestring(s)
n -= len(s)
- for n > 0 {
- if len(zeros) >= n {
- Cwrite(zeros[:n])
- return
- } else {
- Cwrite(zeros[:])
- n -= len(zeros)
- }
+ for n > len(pad) {
+ Cwrite(pad)
+ n -= len(pad)
+
}
+ Cwrite(pad[:n])
}
}
diff --git a/src/cmd/link/internal/x86/asm.go b/src/cmd/link/internal/x86/asm.go
index 2a3513f..cc8f96f 100644
--- a/src/cmd/link/internal/x86/asm.go
+++ b/src/cmd/link/internal/x86/asm.go
@@ -609,7 +609,8 @@
sect := ld.Segtext.Sect
ld.Cseek(int64(sect.Vaddr - ld.Segtext.Vaddr + ld.Segtext.Fileoff))
- ld.Codeblk(int64(sect.Vaddr), int64(sect.Length))
+ // 0xCC is INT $3 - breakpoint instruction
+ ld.CodeblkPad(int64(sect.Vaddr), int64(sect.Length), []byte{0xCC})
for sect = sect.Next; sect != nil; sect = sect.Next {
ld.Cseek(int64(sect.Vaddr - ld.Segtext.Vaddr + ld.Segtext.Fileoff))
ld.Datblk(int64(sect.Vaddr), int64(sect.Length))
