prog: fix shadowing log size variable in verifier log retry loop

When ProgramOptions.LogSize was removed in 0.16, the tests weren't updated to
exercise the retry loop, since a minimum log size was chosen that was larger
than what the test program could generate.

With the addition of LogSizeStart, this notoriously fragile code broke when
logSize was again tracked as a separate variable, while being accidentally
shadowed within the scope of the for loop. This resulted in an endless loop
on kernels without the LogTrueSize field.

Remove the shadowing and fix the tests.

Signed-off-by: Timo Beckers <timo@isovalent.com>

prog.go

@@ -451,7 +451,7 @@ func newProgramWithOptions(spec *ProgramSpec, opts ProgramOptions) (*Program, er
 		// Make an educated guess how large the buffer should be by multiplying.
 		// Ensure the size doesn't overflow.
 		const factor = 2
-		logSize := internal.Between(logSize, minVerifierLogSize, maxVerifierLogSize/factor)
+		logSize = internal.Between(logSize, minVerifierLogSize, maxVerifierLogSize/factor)
 		logSize *= factor
 
 		if attr.LogTrueSize != 0 {

prog_test.go

@@ -469,12 +469,16 @@ func TestProgramVerifierLog(t *testing.T) {
 
 		var ve *internal.VerifierError
 		qt.Assert(t, qt.ErrorAs(err, &ve))
+
+		loglen := len(fmt.Sprintf("%+v", ve))
+		qt.Assert(t, qt.IsTrue(loglen > minVerifierLogSize),
+			qt.Commentf("Log buffer didn't grow past minimum, got %d bytes", loglen))
 	}
 
 	// Generate a base program of sufficient size whose verifier log does not fit
-	// a 128-byte buffer. This should always result in ENOSPC.
+	// in the minimum buffer size. Stay under 4096 insn limit of older kernels.
 	var base asm.Instructions
-	for i := 0; i < 32; i++ {
+	for i := 0; i < 4093; i++ {
 		base = append(base, asm.Mov.Reg(asm.R0, asm.R1))
 	}
 
@@ -493,8 +497,7 @@ func TestProgramVerifierLog(t *testing.T) {
 		Instructions: invalid,
 	}
 
-	// Set an undersized log buffer without explicitly requesting a verifier log
-	// for an invalid program.
+	// Don't explicitly request a verifier log for an invalid program.
 	_, err := NewProgramWithOptions(spec, ProgramOptions{})
 	check(t, err)
 
@@ -528,6 +531,16 @@ func TestProgramVerifierLog(t *testing.T) {
 		LogLevel: LogLevelInstruction,
 	})
 	qt.Assert(t, qt.IsNil(err))
+	qt.Assert(t, qt.IsTrue(len(prog.VerifierLog) > minVerifierLogSize))
+	prog.Close()
+
+	// Repeat the previous test with a larger starting buffer size.
+	prog, err = NewProgramWithOptions(spec, ProgramOptions{
+		LogLevel:     LogLevelInstruction,
+		LogSizeStart: minVerifierLogSize * 2,
+	})
+	qt.Assert(t, qt.IsNil(err))
+	qt.Assert(t, qt.IsTrue(len(prog.VerifierLog) > minVerifierLogSize))
 	prog.Close()
 }