[PATCH] D39021: [llvm-objcopy] Add support for --only-keep/-j and --keep

[Jake Ehrlich via Phabricator via llvm-commits]

jakehehrlich added a comment.

> --only-keep + --strip-sections. Test that the kept section contents are still in the ELF, but not those of .shstrtab. This is to show that the if statement at line 267 does not prevent stripping of the section header strings.

Good idea. This also made me think of a funny case. If you were to run "llvm-objcopy --only-keep=.shstrtab --strip-sections" I think it would produce a file with an elf header and a bit of data containing "\0.shstrtab\0" and nothing else. This is a silly case and that behavior doesn't seem too bad but I found it funny nevertheless.

> I was also going to suggest the following test. However, I realise that with the current behaviour of llvm-objcopy, it's not necessary, because IIRC, --strip-sections does not strip the .shstrtab contents, unless explicitly asked to do so. Is this correct? If so, I suspect that this behaviour needs to change. objcopy rebuilds the section header string table from scratch (and if necessary, splits it from the symbol string table, if the two are merged, like they are in clang's output), removing any redundant entries as it goes. If the section headers have been removed (e.g. via --strip-all), then it completely strips .shstrtab's contents. This is important, because in some cases, leaving the section header strings in the ELF could leak sensitive data to an end user.
> 
> --keep .shstrtab + --strip-sections. Test that the section header strings are still present in the ELF somewhere, even though the section headers have been removed.

--strip-sections removes .shstrtab and sets the flag to indicate that no section headers should be output. Unless --strip-sections is used the section header string table is rebuilt from scratch.  The --keep .shstrtab + --strip-sections would include the string table in the output file but there would be no section header table. If --strip-sections is used then nothing from the string table should make it out. I'll defintl add the --keep .shstrtab + --strip-sections test case but should I also add a test to make sure that --strip-sections doesn't leak section names? Also why should we need to split string table and section header string table?


Repository:
  rL LLVM

https://reviews.llvm.org/D39021