Fix cant found RET offset in gotls mode. fix #502.

[cfc4n]

Fix the issue of not being able to fetch the function RET offset in the gotls model when building a Golang binary with pie mode.

GO_BUILDMODE="-buildmode=pie"

ref: https://github.com/docker/cli/blob/799bf5268039a92c9af197abd612b0f36cf9efe1/scripts/build/.variables#L75C13-L75C42

Here, a constant IdaProOffset = 0x120 is used. I found through IDA static symbol analysis that the address of crypto/tls.(*Conn).Read is 46EE50. The address calculated by the program is always 0x120 less than this number. By analyzing multiple compiled programs, I found that the difference is always 0x120. Therefore, I defined a constant and added it to the address calculated by the program. However, I don't know the reason, if you know, please let me know.

---

这里，使用了一个常量IdaProOffset = 0x120，我是通过IDA静态分析符号发现crypto/tls.(*Conn).Read的地址是46EE50，我用程序计算出来的总是比这个数字少了0x120 ，通过分析其他多个编译的程序，发现差值总是0x120，所以，我定义了一个常量，增加到程序计算的地址上。但是我不知道原因，如果你知道，请告诉我。

func (gc *GoTLSConfig) findPieSymbolAddr(lfunc string) (uint64, error) {
	f := gc.goSymTab.LookupFunc(lfunc)
	if f == nil {
		return 0, errors.New("Cant found symbol address on pie model.")
		// f.Value - prog.Vaddr + prog.Off + IdaProOffset
	}
	var err error
	var address uint64
	for _, prog := range gc.goElf.Progs {
		if prog.Type != elf.PT_LOAD || (prog.Flags&elf.PF_X) == 0 {
			continue
		}
		// For more info on this calculation: stackoverflow.com/a/40249502
		address = f.Value
		if prog.Vaddr <= f.Value && f.Value < (prog.Vaddr+prog.Memsz) {
			funcLen := f.End - f.Entry
			data := make([]byte, funcLen)
			address = f.Value - prog.Vaddr + prog.Off + IdaProOffset
			_, err = prog.ReadAt(data, int64(address))
			if err != nil {
				return 0, fmt.Errorf("search function return: %w", err)
			}
			return address, nil
		}
	}
	return 0, ErrorNoRetFoundFromSymTabFun
}

[sancppp]

Why do I get a could not find magic number error in my test environment?
This error does not occur in the master branch.

As you can see in the picture, my order of operation is right before left.

[cfc4n]

is tests not a ELF file? The pie mode requires enabling CGO.

please use command :

CGO_ENABLED=1 go build -buildmode=pie  -o test main.go

ps:
This PR is not yet complete, I am in the process of optimizing it.

[sancppp]

is tests not a ELF file? The pie mode requires enabling CGO.

please use command :

CGO_ENABLED=1 go build -buildmode=pie  -o test main.go

ps: This PR is not yet complete, I am in the process of optimizing it.

It looks the same as before.

I'm going to wait until this PR is complete before I run these tests, in order to understand what's changed in this PR.

[cfc4n]

reviewed.