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Kevin KrakauerandgVisor bot
c946a298fd
`go tool objdump` produces relative offsets for BL instructions as a number of instructions rather than a number of bytes. Calculate the byte offset ourselves. Example passing run on ARM machine: https://buildkite.com/gvisor/pipeline/builds/14732#018106ac-ac8e-4636-9a5a-bde1641b1175 Filed bug upstream about confusing output here: https://github.com/golang/go/issues/53117 PiperOrigin-RevId: 452137751
70 lines
2.3 KiB
Go
70 lines
2.3 KiB
Go
// Copyright 2022 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package checkescape
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import (
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"fmt"
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"strconv"
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"strings"
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)
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// fixOffset accounts for the output of arm64 `go tool objdump`. Objdump gives
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// the instruction offset rather than the byte offset. The offset confuses
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// checkescape, as it looks like the branch is to random memory.
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//
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// When appropriate, we re-parse the instruction ourselves and return the
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// correct offset.
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func fixOffset(fields []string, target string) (string, error) {
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// We're looking for a line that looks something like:
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// iptables.go:320 0x211214 97f9b198 CALL -413288(PC)
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// In this case, target is passed as -413288(PC). The byte offset of this
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// instruction should be -1653152.
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// Make sure we're dealing with a PC offset.
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if !strings.HasSuffix(target, "(PC)") {
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return target, nil // Not a relative branch.
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}
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// Examine the opcode to ensure it's a BL instruction. See the ARM
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// documentation here:
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// https://developer.arm.com/documentation/ddi0596/2020-12/Base-Instructions/BL--Branch-with-Link-?lang=en
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const (
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opcodeBits = 0xfc000000
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blOpcode = 0x94000000
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)
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instr64, err := strconv.ParseUint(fields[2], 16, 32)
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if err != nil {
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return "", err
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}
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instr := uint32(instr64)
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if instr&opcodeBits != blOpcode {
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return target, nil // Not a BL.
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}
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// Per documentation, the offset is formed via:
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// - Take the lower 26 bits
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// - Append 2 zero bits (this is what objdump omits)
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// - Sign extend out to 64 bits
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offset := int64(int32(instr<<6) >> 4)
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// Parse the PC, removing the leading "0x".
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pc, err := strconv.ParseUint(fields[1][len("0x"):], 16, 64)
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if err != nil {
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return "", err
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}
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// PC is always the next instruction.
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pc += 8
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return fmt.Sprintf("0x%x", pc+uint64(offset)), nil
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}
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