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Update CALL/CALLARM64 relocs - try JMP (to epilogue) then CALL (targe…
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…t func) then JMP (back from epilogue) instead of CALL (into epilogue) then JMP (into target func), since if a traceback hits while we're in the epilogue, the funcForPC for the current PC will not be aligned with the link register (regardlesswhether the LR is virtual or real), and it will appear that the callee and caller are the same `_func`
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Anonymous committed Sep 6, 2023
1 parent 30ad044 commit c55452a
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Showing 6 changed files with 78 additions and 20 deletions.
16 changes: 10 additions & 6 deletions asm_bytes.go
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Original file line number Diff line number Diff line change
Expand Up @@ -17,8 +17,9 @@ var (
// since Go only uses them for the stack prologue and epilogue calculations,
// and we should already be clear of that by the time we hit a R_CALLARM64,
// so we should be able to safely use them for far jumps
0x51, 0x00, 0x00, 0x58, // LDR X17 [PC+8] - read 64 bit address from PC+8 into X17
0x20, 0x02, 0x1f, 0xd6, // BR X17 - jump to address in X17
0x71, 0x00, 0x00, 0x58, // LDR X17 [PC+12] - read 64 bit address from PC+12 into X17
0x20, 0x02, 0x3f, 0xd6, // BLR X17 - linked branch (call) to address in X17
0x00, 0x00, 0x00, 0x14, // B [PC+0x0] (linkless branch (jump) back from epilogue)
}
arm64Bcode = []byte{0x00, 0x00, 0x00, 0x14} // B [PC+0x0]
arm64NopCode = []byte{0x1f, 0x20, 0x03, 0xd5}
Expand All @@ -31,10 +32,13 @@ const (

// x86/amd64
var (
x86amd64NOPcode = byte(0x90)
x86amd64JMPLcode = []byte{0xff, 0x25, 0x00, 0x00, 0x00, 0x00} // JMPL *ADDRESS
x86amd64JMPNearCode = []byte{0xE9, 0x00, 0x00, 0x00, 0x00} // JMP (PCREL offset)+4
x86amd64JMPShortCode = []byte{0xEB, 0x00} // JMP (PCREL offset)+1
x86amd64NOPcode = byte(0x90)
x86amd64JMPLcode = []byte{0xff, 0x25, 0x00, 0x00, 0x00, 0x00} // JMPL *ADDRESS
x86amd64JMPNearCode = []byte{0xE9, 0x00, 0x00, 0x00, 0x00} // JMP (PCREL offset)+4
x86amd64JMPShortCode = []byte{0xEB, 0x00} // JMP (PCREL offset)+1
x86amd64CALLFarCode = []byte{
0xff, 0x15, 0x00, 0x00, 0x00, 0x00, // CALL ptr [RIP]
}
x86amd64replaceCMPLcode = []byte{
0x50, // PUSH RAX
0x48, 0xb8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // MOVABS RAX, imm64 (64 bit)
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2 changes: 1 addition & 1 deletion jit/go.mod
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Expand Up @@ -10,5 +10,5 @@ require (

require github.com/opentracing/opentracing-go v1.2.0 // indirect

//replace github.com/eh-steve/goloader => ../
replace github.com/eh-steve/goloader => ../
//replace github.com/eh-steve/goloader/jit/testdata => ./testdata
1 change: 1 addition & 0 deletions jit/jit_test.go
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Expand Up @@ -311,6 +311,7 @@ func TestJitEmbeddedStruct(t *testing.T) {
}

func TestSchedule(t *testing.T) {
t.Skip("this takes forever")
conf := baseConfig
data := testData{
files: []string{"./testdata/test_schedule/test.go"},
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19 changes: 16 additions & 3 deletions ld.go
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Original file line number Diff line number Diff line change
Expand Up @@ -330,11 +330,14 @@ func (linker *Linker) addSymbol(name string, globalSymPtr map[string]uintptr) (s
case x86amd64CALL2code: // CGo FF 15 PCREL call
if instructionBytes[1] == 0x15 {
epilogueSize = maxExtraInstructionBytesPCRELxCALL2
break
}
fallthrough // Might be FF XX E8/E9 ...
default:
switch instructionBytes[1] {
case x86amd64CALLcode:
epilogueSize = maxExtraInstructionBytesPCRELxCALL
opcode = x86amd64CALLcode
epilogueSize = maxExtraInstructionBytesCALLNear
case x86amd64JMPcode:
epilogueSize = maxExtraInstructionBytesPCRELxJMP
}
Expand All @@ -350,6 +353,10 @@ func (linker *Linker) addSymbol(name string, globalSymPtr map[string]uintptr) (s
if shortJmp {
epilogueSize = maxExtraInstructionBytesPCRELxCMPLShort
}
case x86amd64CALLcode:
if shortJmp {
epilogueSize = maxExtraInstructionBytesCALLShort
}
}
objsym.Reloc[i].EpilogueSize = epilogueSize
linker.code = append(linker.code, createArchNops(linker.Arch, epilogueSize)...)
Expand All @@ -364,9 +371,15 @@ func (linker *Linker) addSymbol(name string, globalSymPtr map[string]uintptr) (s
alignment := alignof(len(linker.code)-symbol.Offset, PtrSize) - (len(linker.code) - symbol.Offset)
linker.code = append(linker.code, createArchNops(linker.Arch, objsym.Reloc[i].EpilogueSize+alignment)...)
case reloctype.R_CALL, reloctype.R_CALL | reloctype.R_WEAK:
epilogueSize := maxExtraInstructionBytesCALLNear
returnOffset := (reloc.Offset + reloc.Size) - (objsym.Reloc[i].EpilogueOffset + epilogueSize) - len(x86amd64JMPShortCode) // assumes short jump, adjusts if not
shortJmp := returnOffset < 0 && returnOffset > -0x80
objsym.Reloc[i].EpilogueOffset = len(linker.code) - symbol.Offset
objsym.Reloc[i].EpilogueSize = maxExtraInstructionBytesCALL
linker.code = append(linker.code, createArchNops(linker.Arch, maxExtraInstructionBytesCALL)...)
if shortJmp {
epilogueSize = maxExtraInstructionBytesCALLShort
}
objsym.Reloc[i].EpilogueSize = epilogueSize
linker.code = append(linker.code, createArchNops(linker.Arch, epilogueSize)...)
}
bytearrayAlignNops(linker.Arch, &linker.code, PtrSize)
}
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58 changes: 49 additions & 9 deletions relocate.go
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Original file line number Diff line number Diff line change
Expand Up @@ -21,10 +21,10 @@ var (
maxExtraInstructionBytesPCRELxMOVNear = len(x86amd64replaceMOVQcode) + len(x86amd64JMPNearCode)
maxExtraInstructionBytesPCRELxCMPLShort = len(x86amd64replaceCMPLcode) + len(x86amd64JMPShortCode)
maxExtraInstructionBytesPCRELxCMPLNear = len(x86amd64replaceCMPLcode) + len(x86amd64JMPNearCode)
maxExtraInstructionBytesPCRELxCALL = len(x86amd64JMPLcode) + PtrSize
maxExtraInstructionBytesPCRELxCALL2 = PtrSize
maxExtraInstructionBytesPCRELxJMP = len(x86amd64JMPLcode) + PtrSize
maxExtraInstructionBytesCALL = len(x86amd64JMPLcode) + PtrSize
maxExtraInstructionBytesCALLShort = len(x86amd64CALLFarCode) + len(x86amd64JMPShortCode) + PtrSize
maxExtraInstructionBytesCALLNear = len(x86amd64CALLFarCode) + len(x86amd64JMPNearCode) + PtrSize
maxExtraInstructionBytesGOTPCREL = PtrSize
maxExtraInstructionBytesARM64GOTPCREL = PtrSize
)
Expand Down Expand Up @@ -140,14 +140,28 @@ func (linker *Linker) relocateCALL(addr uintptr, loc obj.Reloc, segment *segment
copy(segment.codeByte[epilogueOffset:epilogueOffset+loc.EpilogueSize], createX86Nops(loc.EpilogueSize))

if offset > 0x7FFFFFFF || offset < -0x80000000 || (linker.options.ForceTestRelocationEpilogues && loc.EpilogueSize > 0) {
// "CALL" into the epilogue, then immediately JMPL into the actual func using a PCREL 8 byte
// address immediately after the epilogue - the RET will bring us straight back to the call site
// JMP into the epilogue, then CALL into the actual func using a PCREL 8 byte address placed after the JMP back from the epilogue
if loc.EpilogueSize == 0 {
return fmt.Errorf("relocation epilogue not available but got a >32-bit CALL reloc (x86 code: %x) with offset %d: %s", relocByte[loc.Offset-2:loc.Offset+loc.Size], offset, loc.Sym.Name)
}
offset = (segment.codeBase + epilogueOffset) - (addrBase + loc.Offset + loc.Size)
copy(segment.codeByte[epilogueOffset:], x86amd64JMPLcode)
epilogueOffset += len(x86amd64JMPLcode)
// Replace the E8 CALL with a E9 JMP into the epilogue, the CALL the function, then JMP (near or far) back
relocByte[loc.Offset-1] = x86amd64JMPcode
offset = (segment.codeBase + epilogueOffset) - (addrBase + loc.Offset + loc.Size) // Point the JMP offset at the epilogue
copy(segment.codeByte[epilogueOffset:], x86amd64CALLFarCode)
epilogueOffset += len(x86amd64CALLFarCode)
returnOffset := (loc.Offset + loc.Size) - epilogueOffset - len(x86amd64JMPShortCode) // assumes short jump - if we need a near jump, we'll adjust
if returnOffset > -0x80 && returnOffset < 0 {
byteorder.PutUint32(relocByte[epilogueOffset-4:], uint32(len(x86amd64JMPShortCode))) // Read the 8 bytes after the length of the JMP back
copy(segment.codeByte[epilogueOffset:], x86amd64JMPShortCode)
segment.codeByte[epilogueOffset+1] = uint8(returnOffset)
epilogueOffset += len(x86amd64JMPShortCode)
} else {
byteorder.PutUint32(relocByte[epilogueOffset-4:], uint32(len(x86amd64JMPNearCode))) // Read the 8 bytes after the length of the JMP back
returnOffset -= len(x86amd64JMPNearCode) - len(x86amd64JMPShortCode)
copy(segment.codeByte[epilogueOffset:], x86amd64JMPNearCode)
byteorder.PutUint32(segment.codeByte[epilogueOffset+1:], uint32(returnOffset))
epilogueOffset += len(x86amd64JMPNearCode)
}
putAddressAddOffset(byteorder, segment.codeByte, &epilogueOffset, uint64(addr)+uint64(loc.Add))
}
byteorder.PutUint32(relocByte[loc.Offset:], uint32(offset))
Expand Down Expand Up @@ -233,8 +247,23 @@ func (linker *Linker) relocatePCREL(addr uintptr, loc obj.Reloc, segment *segmen
epilogueOffset += len(x86amd64replaceMOVQcode)
}
case x86amd64CALLcode:
copy(segment.codeByte[epilogueOffset:], x86amd64JMPLcode)
epilogueOffset += len(x86amd64JMPLcode)
bytes[1] = x86amd64JMPcode
offset = (segment.codeBase + epilogueOffset) - (addrBase + loc.Offset + loc.Size) // Point the JMP offset at the epilogue
copy(segment.codeByte[epilogueOffset:], x86amd64CALLFarCode)
epilogueOffset += len(x86amd64CALLFarCode)
returnOffset := (loc.Offset + loc.Size) - epilogueOffset - len(x86amd64JMPShortCode) // assumes short jump - if we need a near jump, we'll adjust
if returnOffset > -0x80 && returnOffset < 0 {
byteorder.PutUint32(relocByte[epilogueOffset-4:], uint32(len(x86amd64JMPShortCode))) // Read the 8 bytes after the length of the JMP back
copy(segment.codeByte[epilogueOffset:], x86amd64JMPShortCode)
segment.codeByte[epilogueOffset+1] = uint8(returnOffset)
epilogueOffset += len(x86amd64JMPShortCode)
} else {
byteorder.PutUint32(relocByte[epilogueOffset-4:], uint32(len(x86amd64JMPNearCode))) // Read the 8 bytes after the length of the JMP back
returnOffset -= len(x86amd64JMPNearCode) - len(x86amd64JMPShortCode)
copy(segment.codeByte[epilogueOffset:], x86amd64JMPNearCode)
byteorder.PutUint32(segment.codeByte[epilogueOffset+1:], uint32(returnOffset))
epilogueOffset += len(x86amd64JMPNearCode)
}
putAddressAddOffset(byteorder, segment.codeByte, &epilogueOffset, uint64(addr)+uint64(loc.Add))
case x86amd64CALL2code:
putAddressAddOffset(byteorder, segment.codeByte, &epilogueOffset, uint64(addr)+uint64(loc.Add))
Expand Down Expand Up @@ -287,10 +316,21 @@ func (linker *Linker) relocateCALLARM(addr uintptr, loc obj.Reloc, segment *segm
add = int(signext24(int64(loc.Add&0xFFFFFF)+2) * 4)
off = uint32(epilogueOffset-loc.Offset-8) / 4
}
// Replace the BL with a linkless branch (JMP) into the epilogue
copy(segment.codeByte[loc.Offset:], arm64Bcode)
putUint24(segment.codeByte[loc.Offset:], off)
if loc.Type == reloctype.R_CALLARM64 {
// LDR X17 [PC+12]
// BLR X17
// BL [PC-epilogueOffset]
copy(segment.codeByte[epilogueOffset:], arm64CALLCode)
epilogueOffset += len(arm64CALLCode)
bcode := byteorder.Uint32(segment.codeByte[epilogueOffset-4:]) // Unconditional branch
bcode |= ((uint32(loc.Offset+8) - uint32(epilogueOffset)) >> 2) & 0x01FFFFFF
if loc.Offset+8-epilogueOffset < 0 {
bcode |= 0x02000000 // 26th bit is sign bit
}
byteorder.PutUint32(segment.codeByte[epilogueOffset-4:], bcode)
} else {
copy(segment.codeByte[epilogueOffset:], armcode)
epilogueOffset += len(armcode)
Expand Down
2 changes: 1 addition & 1 deletion utils.go
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Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,7 @@ func createARM64Nops(size int) []byte {
}

nops := make([]byte, size)
for i := 0; i < size/4; i += 4 {
for i := 0; i < size; i += 4 {
copy(nops[i:], arm64NopCode)
}
return nops
Expand Down

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