From edd756a5fa6390fb08e2b515e507253a59b22d70 Mon Sep 17 00:00:00 2001
From: Alexander Potapenko <glider@google.com>
Date: Wed, 13 Dec 2023 16:55:18 +0100
Subject: pkg/cover/backend: retire pcFixUpOffset

Adjusting the module pc by 0x18 is a poorly documented hack that relies
on the fixed .plt size. Remove it in favor of a more flexible solution.
---
 pkg/cover/backend/dwarf.go | 22 +++++++---------------
 pkg/cover/backend/elf.go   | 21 ---------------------
 2 files changed, 7 insertions(+), 36 deletions(-)

(limited to 'pkg')

diff --git a/pkg/cover/backend/dwarf.go b/pkg/cover/backend/dwarf.go
index 9f36cdfa6..4db2f2ad4 100644
--- a/pkg/cover/backend/dwarf.go
+++ b/pkg/cover/backend/dwarf.go
@@ -24,16 +24,12 @@ import (
 )
 
 type dwarfParams struct {
-	target      *targets.Target
-	objDir      string
-	srcDir      string
-	buildDir    string
-	moduleObj   []string
-	hostModules []host.KernelModule
-	// Kernel coverage PCs in the [pcFixUpStart,pcFixUpEnd) range are offsetted by pcFixUpOffset.
-	pcFixUpStart          uint64
-	pcFixUpEnd            uint64
-	pcFixUpOffset         uint64
+	target                *targets.Target
+	objDir                string
+	srcDir                string
+	buildDir              string
+	moduleObj             []string
+	hostModules           []host.KernelModule
 	readSymbols           func(*Module, *symbolInfo) ([]*Symbol, error)
 	readTextData          func(*Module) ([]byte, error)
 	readModuleCoverPoints func(*targets.Target, *Module, *symbolInfo) ([2][]uint64, error)
@@ -209,11 +205,7 @@ func makeDWARFUnsafe(params *dwarfParams) (*Impl, error) {
 
 func makeRestorePC(params *dwarfParams, pcBase uint64) func(pc uint32) uint64 {
 	return func(pcLow uint32) uint64 {
-		pc := PreviousInstructionPC(params.target, RestorePC(pcLow, uint32(pcBase>>32)))
-		if pc >= params.pcFixUpStart && pc < params.pcFixUpEnd {
-			pc -= params.pcFixUpOffset
-		}
-		return pc
+		return PreviousInstructionPC(params.target, RestorePC(pcLow, uint32(pcBase>>32)))
 	}
 }
 
diff --git a/pkg/cover/backend/elf.go b/pkg/cover/backend/elf.go
index c9a02aba4..57975a9d5 100644
--- a/pkg/cover/backend/elf.go
+++ b/pkg/cover/backend/elf.go
@@ -8,7 +8,6 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io"
-	"path/filepath"
 	"strings"
 
 	"github.com/google/syzkaller/pkg/host"
@@ -18,23 +17,6 @@ import (
 
 func makeELF(target *targets.Target, objDir, srcDir, buildDir string,
 	moduleObj []string, hostModules []host.KernelModule) (*Impl, error) {
-	var pcFixUpStart, pcFixUpEnd, pcFixUpOffset uint64
-	if target.Arch == targets.ARM64 {
-		// On arm64 as PLT is enabled by default, .text section is loaded after .plt section,
-		// so there is 0x18 bytes offset from module load address for .text section
-		// we need to remove the 0x18 bytes offset in order to correct module symbol address
-		// TODO: obtain these values from the binary instead of hardcoding.
-		file, err := elf.Open(filepath.Join(objDir, target.KernelObject))
-		if err != nil {
-			return nil, err
-		}
-		defer file.Close()
-		if file.Section(".plt") != nil {
-			pcFixUpStart = 0x8000000000000000
-			pcFixUpEnd = 0xffffffd010000000
-			pcFixUpOffset = 0x18
-		}
-	}
 	return makeDWARF(&dwarfParams{
 		target:                target,
 		objDir:                objDir,
@@ -42,9 +24,6 @@ func makeELF(target *targets.Target, objDir, srcDir, buildDir string,
 		buildDir:              buildDir,
 		moduleObj:             moduleObj,
 		hostModules:           hostModules,
-		pcFixUpStart:          pcFixUpStart,
-		pcFixUpEnd:            pcFixUpEnd,
-		pcFixUpOffset:         pcFixUpOffset,
 		readSymbols:           elfReadSymbols,
 		readTextData:          elfReadTextData,
 		readModuleCoverPoints: elfReadModuleCoverPoints,
-- 
cgit mrf-deployment