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prog: get context out from syscall program #1803

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prog: get context out from syscall program #1803

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10 changes: 10 additions & 0 deletions prog.go
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Original file line number Diff line number Diff line change
Expand Up @@ -884,6 +884,16 @@ func (p *Program) run(opts *RunOptions) (uint32, time.Duration, error) {
Cpu: opts.CPU,
}

if p.Type() == Syscall && ctxIn != nil && ctxOut != nil {
// Linux syscall program errors on non-nil ctxOut, uses ctxIn
// for both input and output. Shield the user from this wart.
if len(ctxIn) != len(ctxOut) {
return 0, 0, errors.New("length mismatch: Context and ContextOut")
}
attr.CtxOut, attr.CtxSizeOut = sys.TypedPointer[uint8]{}, 0
ctxOut = ctxIn
}

retry:
for {
err := sys.ProgRun(&attr)
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35 changes: 35 additions & 0 deletions prog_linux_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@ import (

"github.com/cilium/ebpf/asm"
"github.com/cilium/ebpf/internal"
"github.com/cilium/ebpf/internal/sys"
"github.com/cilium/ebpf/internal/testutils"
"github.com/cilium/ebpf/internal/unix"
)
Expand Down Expand Up @@ -135,3 +136,37 @@ func TestProgramVerifierLogLinux(t *testing.T) {
})
qt.Assert(t, qt.IsTrue(len(prog.VerifierLog) > minVerifierLogSize))
}

func TestProgramTestRunSyscall(t *testing.T) {
testutils.SkipOnOldKernel(t, "5.14", "BPF_PROG_TYPE_SYSCALL")

prog := mustNewProgram(t, &ProgramSpec{
Type: Syscall,
Flags: sys.BPF_F_SLEEPABLE,
License: "MIT",
Instructions: []asm.Instruction{
// fn (ctx *u64) { *ctx++; return *ctx }
asm.LoadMem(asm.R0, asm.R1, 0, asm.DWord),
asm.Add.Imm(asm.R0, 1),
asm.StoreMem(asm.R1, 0, asm.R0, asm.DWord),
asm.Return(),
},
}, nil)

// only Context
rc, err := prog.Run(&RunOptions{Context: uint64(42)})
testutils.SkipIfNotSupported(t, err)
if err != nil {
t.Fatal(err)
}
qt.Assert(t, qt.Equals(rc, 43))

// Context and ContextOut
out := uint64(0)
rc, err = prog.Run(&RunOptions{Context: uint64(99), ContextOut: &out})
if err != nil {
t.Fatal(err)
}
qt.Assert(t, qt.Equals(rc, 100))
qt.Assert(t, qt.Equals(out, 100))
}
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