No libc.sym.__libc_start_main_ret while libcdb reports it

[tesuji]

> libcdb file /lib/x86_64-linux-gnu/libc.so.6
[*] libc.so.6
    Version:     2.41
    BuildID:     beada22c75281a7e3ed0847c8ba3b2a28bddfe6c
    MD5:         56507c022fb7bd983d49e9e704db4aa1
    SHA1:        b6f98582f06859632f750cbcfd1b95d884ca8b19
    SHA256:      826b5033b9ad60b026cc7fce0d6eacb48de13aaa950f5f5d3a6711aba9ef224a
    Symbols:
        __libc_start_main_ret = 0x29ca8
                         dup2 = 0xff840
                       printf = 0x59880
                         puts = 0x80520
                         read = 0x103e90
                   str_bin_sh = 0x1a7ea4
                       system = 0x530d0
                        write = 0x104920

However, using ELF(libc_path).sym.__libc_start_main_ret raises a not-found exception.
It would be nice if we could automatically set this for ELF(libc).

[tesuji]

LMAO. I found this in the doc: https://docs.pwntools.com/en/stable/elf/elf.html#pwnlib.elf.elf.ELF.libc_start_main_return
However, I still feel that automatically setting this on ELF(libc).sym is really nice to have.

[peace-maker]

I didn't add it to the ELF.symbols by default since disassembling some code potentially twice takes time and I didn't want to slow down the average case of not using that symbol.

Some heuristic if the ELF is a libc could be cheap, so maybe lazily adding that symbol to the symbols dotdict somehow could work? To only look up the actual value if the code requests it.

[tesuji]

What about raising an exception when accessing that virtual index to guide user towards ELF.libc_start_main_return ?

[peace-maker]

That's a good start to make this more discoverable. Would you be willing to submit a PR for this against stable please?

We can add lazy calculating the property later.