I'm seeing the following panic on both Go 1.20.7 and Go 1.21.0 (amd64):
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x46e421]
goroutine 368 [running]:
type:.hash.redacted.com/redacted/redacted.componentKey(0xc001b37de8,
0xc001b37d68?)
<autogenerated>:1 +0x2c
redacted.com/redacted/redacted.(*redactedType[...]).redactedMethod1(0x1481900,
0xc0046c6a20)
redacted/redacted.go:182 +0x2c5
redacted.com/redacted/redacted.(*redactedType[...]).redactedMethod2(0x1481900)
redacted/redacted.go:141 +0x5c
created by redacted.com/redacted.NewRedactedType[...] in goroutine 1
redacted/redacted.go:99 +0x165
componentKey is:
type componentKey struct {
a string
b string
}
Line 182 is:
myMap[myComponentKey] += 1
where myMap is of type map[componentKey]int64, and myComponentKey is of
type componentKey.
As I understand it:
1. The issue is not that myMap is nil; if that were the case, the panic
would read `assignment to entry in nil map`
2. The nil dereference is coming from the hash function that the compiler
autogenerated for componentKey, which looks something like this (Go 1.21):
TEXT type:.hash.main.componentKey(SB) <autogenerated>
<autogenerated>:1 0x457780 493b6610
CMPQ SP, 0x10(R14)
<autogenerated>:1 0x457784 762c JBE
0x4577b2
<autogenerated>:1 0x457786 55
PUSHQ BP
<autogenerated>:1 0x457787 4889e5
MOVQ SP, BP
<autogenerated>:1 0x45778a 4883ec10
SUBQ $0x10, SP
<autogenerated>:1 0x45778e 4889442420
MOVQ AX, 0x20(SP)
<autogenerated>:1 0x457793 e808d0ffff
CALL runtime.strhash(SB)
<autogenerated>:1 0x457798 488b4c2420
MOVQ 0x20(SP), CX
<autogenerated>:1 0x45779d 4883c110
ADDQ $0x10, CX
<autogenerated>:1 0x4577a1 4889c3
MOVQ AX, BX
<autogenerated>:1 0x4577a4 4889c8
MOVQ CX, AX
<autogenerated>:1 0x4577a7 e8f4cfffff
CALL runtime.strhash(SB)
<autogenerated>:1 0x4577ac 4883c410
ADDQ $0x10, SP
<autogenerated>:1 0x4577b0 5d
POPQ BP
<autogenerated>:1 0x4577b1 c3 RET
<autogenerated>:1 0x4577b2 4889442408
MOVQ AX, 0x8(SP)
<autogenerated>:1 0x4577b7 48895c2410
MOVQ BX, 0x10(SP)
<autogenerated>:1 0x4577bc 0f1f4000
NOPL 0(AX)
<autogenerated>:1 0x4577c0 e8fbcdffff
CALL runtime.morestack_noctxt.abi0(SB)
<autogenerated>:1 0x4577c5 488b442408
MOVQ 0x8(SP), AX
<autogenerated>:1 0x4577ca 488b5c2410
MOVQ 0x10(SP), BX
<autogenerated>:1 0x4577cf ebaf JMP
type:.hash.main.componentKey(SB)
I'm having difficulty understanding how this code could produce a nil
dereference, unless some runtime assumptions are being violated (maybe the
string pointer and length are out of sync due to a data race)?
Thanks very much for your time.
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