4 ms·

Don't do this, it's ugly and relies on assumptions that aren't true. I haven't checked each spec, but it is very unlikely that your ELF/mach-O/PE/... is still v

by anyfoo 4y ago

Don't do this, it's ugly and relies on assumptions that aren't true. I haven't checked each spec, but it is very unlikely that your ELF/mach-O/PE/... is still valid with added junk at the end. You may try it out and it may work, but that is true for many things that may come back to bite you (or others) in spectacular ways.

fabian2k 4y ago
I'd be interested in any example where this approach would produce an invalid executable. I have used this without issues, but of course I have certainly not tried this in every possible environment.
- anyfoo 4y ago
  Computing history is chock full of examples where something "seems to work" but is actually invalid (and a mach-O treated that way would be invalid [EDIT: or just "not accepted" by some parts of the system, see below], whether it runs or not), and then Raymond Chen has to write a blog post about it decades later. Here's just one out of many as a random example: https://devblogs.microsoft.com/oldnewthing/20041026-00/?p=37473 https://devblogs.microsoft.com/oldnewthing/20041026-00/?p=37... Back to this particular case, the binary will fail strict code signing validation on macOS. It may still run because the kernel does not access the binary past the coverage of the code signature (and all the bits there are still intact), similar to how multiarch binaries work, but you will at least severely be hampered to distribute your binary, since Gatekeeper won't be happy either.
dmitrygr 4y ago
> it is very unlikely that your ELF/mach-O/PE/... is still valid with added junk at the end. I've written loaders for all of the executable formats you mentioned, and maybe a dozen more. I know of none where this would violate the strict interpretation of the word of the spec. That being said, valid file != happy OS
- anyfoo 4y ago
  Agreed. As above: It may for example run, but not be accepted by other parts of the OS (as evidenced).

by anyfoo 4y ago

fabian2k 4y ago

I'd be interested in any example where this approach would produce an invalid executable. I have used this without issues, but of course I have certainly not tried this in every possible environment.

anyfoo 4y ago
Computing history is chock full of examples where something "seems to work" but is actually invalid (and a mach-O treated that way would be invalid [EDIT: or just "not accepted" by some parts of the system, see below], whether it runs or not), and then Raymond Chen has to write a blog post about it decades later. Here's just one out of many as a random example: https://devblogs.microsoft.com/oldnewthing/20041026-00/?p=37473 https://devblogs.microsoft.com/oldnewthing/20041026-00/?p=37... Back to this particular case, the binary will fail strict code signing validation on macOS. It may still run because the kernel does not access the binary past the coverage of the code signature (and all the bits there are still intact), similar to how multiarch binaries work, but you will at least severely be hampered to distribute your binary, since Gatekeeper won't be happy either.

dmitrygr 4y ago

> it is very unlikely that your ELF/mach-O/PE/... is still valid with added junk at the end. I've written loaders for all of the executable formats you mentioned, and maybe a dozen more. I know of none where this would violate the strict interpretation of the word of the spec. That being said, valid file != happy OS

anyfoo 4y ago
Agreed. As above: It may for example run, but not be accepted by other parts of the OS (as evidenced).