math/big: `signal SIGSEGV: segmentation violation` when using multi-line strings.

[agiUnderground]

What version of Go are you using (go version)?

$ go version
go version go1.20.4 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
macos Ventura 13.3.1 Darwin Kernel Version 22.4.0
x86_64

What did you do?

package main

import (
	"fmt"
	mb "math/big"
)

func main() {
	a := mb.NewInt(0)
	b := mb.NewInt(0)
	c := mb.NewInt(0)
	a, _ = a.SetString(`93495878923078976349082734823469324758967234678569
                           62387685983479898989898989899899898998989889899898
                           98989898989989898989898989899898988989898989898989
                           89898988989898989889898989989898989879879879`, 10);
	b, _ = b.SetString(`9999999949532798763428068937249324976893467324785
                           67843264876432598734698572634856923599999999983493
                           49683247986789324769438726463080980980908998798798
                           797897987987987979878978979878897987897789789`, 10);
	c.Add(a, b);
	fmt.Println(c);
}

https://play.golang.com/p/06JOoCfsT0D

What did you expect to see?

193495878418406963983363424195962574527901907926426408203347478058863368847162484691349989898897348339582237885788314668428625453070879879898897788697787796976977886969768877969868796977777669668

What did you see instead?

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x484d7d]

goroutine 1 [running]:
math/big.(*Int).Add(0xc000060020, 0x4b84a0?, 0x116?)
	/usr/local/go-faketime/src/math/big/int.go:135 +0x1d
main.main()
	/tmp/sandbox4028842665/prog.go:20 +0xe5

It is working with a regular strings formatted in one line, but with this multi-line backtick format it fails.

[shmsr]

Here SetString fails in your case i.e., the value of a and b is undefined and the returned value is nil hence panic is expected. Do not ignore the return value (bool) of SetString.

[agiUnderground]

@shmsr But why it is working as expected with a regular strings?

package main

import (
	"fmt"
	mb "math/big"
)

func main() {
	a := mb.NewInt(0);
	b := mb.NewInt(0);
	c := mb.NewInt(0);
	a, _ = a.SetString("93495878923078976349082734823469324758967234678569623876859834798989898989898998998989989898898998989898989898998989898989898989989898898989898989898989898988989898989889898989989898989879879879", 10);
	b, _ = b.SetString("99999999495327987634280689372493249768934673247856784326487643259873469857263485692359999999998349349683247986789324769438726463080980980908998798798797897987987987979878978979878897987897789789", 10);
	c.Add(a, b);
	fmt.Println(c);
}

[ianlancetaylor]

Your multi-line strings have whitespace in them, and SetString doesn't permit whitespace.

Always check the error result.