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proc: fix RFLAGS corruption after call injection on amd64 (#3002)

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debugCallV2 for amd64 has a bug where it corrupts the flags registers
every time it is called, this commit works around that problem by
restoring flags one extra time to its original value after stepping out
of debugCallV2.

Fixes #2985
This commit is contained in:
Alessandro Arzilli
2022-05-05 17:41:40 +02:00
committed by GitHub
parent 51090f003b
commit b53fcbe43a
6 changed files with 98 additions and 1 deletions
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56
pkg/proc/proc_test.go
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@ -5852,3 +5852,59 @@ func TestStepIntoAutogeneratedSkip(t *testing.T) {
assertLineNumber(p, t, 12, "After step")
})
}
func TestCallInjectionFlagCorruption(t *testing.T) {
// debugCallV2 has a bug in amd64 where its tail corrupts the FLAGS register by running an ADD instruction.
// Since this problem exists in many versions of Go, instead of fixing
// debugCallV2, we work around this problem by restoring FLAGS, one extra
// time, after stepping out of debugCallV2.
// Fixes issue https://github.com/go-delve/delve/issues/2985
skipUnlessOn(t, "not relevant", "amd64")
withTestProcessArgs("badflags", t, ".", []string{"0"}, 0, func(p *proc.Target, fixture protest.Fixture) {
mainfn := p.BinInfo().LookupFunc["main.main"]
// Find JNZ instruction on line :14
var addr uint64
text, err := proc.Disassemble(p.Memory(), nil, p.Breakpoints(), p.BinInfo(), mainfn.Entry, mainfn.End)
assertNoError(err, t, "Disassemble")
for _, instr := range text {
if instr.Loc.Line != 14 {
continue
}
if proc.IsJNZ(instr.Inst) {
addr = instr.Loc.PC
}
}
if addr == 0 {
t.Fatalf("Could not find JNZ instruction at line :14")
}
// Create breakpoint
_, err = p.SetBreakpoint(0, addr, proc.UserBreakpoint, nil)
assertNoError(err, t, "SetBreakpoint")
// Continue to breakpoint
assertNoError(p.Continue(), t, "Continue()")
assertLineNumber(p, t, 14, "expected line :14")
// Save RFLAGS register
rflagsBeforeCall := p.BinInfo().Arch.RegistersToDwarfRegisters(0, getRegisters(p, t)).Uint64Val(regnum.AMD64_Rflags)
t.Logf("rflags before = %#x", rflagsBeforeCall)
// Inject call to main.g()
assertNoError(proc.EvalExpressionWithCalls(p, p.SelectedGoroutine(), "g()", normalLoadConfig, true), t, "Call")
// Check RFLAGS register after the call
rflagsAfterCall := p.BinInfo().Arch.RegistersToDwarfRegisters(0, getRegisters(p, t)).Uint64Val(regnum.AMD64_Rflags)
t.Logf("rflags after = %#x", rflagsAfterCall)
if rflagsBeforeCall != rflagsAfterCall {
t.Errorf("mismatched rflags value")
}
// Single step and check where we end up
assertNoError(p.Step(), t, "Step()")
assertLineNumber(p, t, 17, "expected line :17") // since we passed "0" as argument we should be going into the false branch at line :17
})
}