[llvm-dev] llvm-objcopy round-table summary (original) (raw)

James Henderson via llvm-dev llvm-dev at lists.llvm.org
Mon Oct 22 04:34:53 PDT 2018

Action: James Henderson to provide results of feature comparison versus GNU objcopy.

A couple of weeks ago, I did an analysis of the GNU objcopy command-line switches versus the llvm-objcopy ones. I did not go into depth to compare behaviour of the individual switches - I only verified that such switches exist. Following are my results. It's worth noting that a number of missing features are for file formats that llvm-objcopy does not currently support (especially COFF).

GNU feature/option | llvm-objcopy feature/ | Notes | option | ===========================+============================+=========

objcopy | llvm-objcopy | objcopy | llvm-objcopy | | | -I/--input-target | -I--input-target | "binary" only -O/--output-target | -O/--output-target | "binary"/ELF only -B/--binary-architecture | -B/--binary-architecture | -F/--target | -F/--target | --debugging | None available | -p/--preserve-dates | -p/--preserve-dates | -j/--only-section | -j/--only-section | --add-gnu-debuglink | --add-gnu-debuglink | -R/--remove-section | -R/--remove-section | -S/--strip-all | -S/--strip-all | --strip-all-gnu is | | closer to GNU objcopy -g/--strip-debug | --strip-debug | '-g' not supported --strip-unneeded | --strip-unneeded | -N/--strip-symbol | -N/--strip-symbol | --strip-unneeded-symbol | None available | --only-keep-debug | --only-keep-debug | --extract-symbol | None available | -K/--keep-symbol | -K/--keep-symbol | --keep-file-symbols | --keep-file-symbols | --localize-hidden | --localize-hidden | -L/--localize-symbol | -L/--localize-symbol | --globalize-symbol | --globalize-symbol | -G/--keep-global-symbol | -G/--keep-global-symbol | -W/--weaken-symbol | -W/--weaken-symbol | --weaken | --weaken | -w/--wildcard | None available | -x/--discard-all | -x/--discard-all | -X/--discard-locals | None available | -i/--interleave | None available | --interleave-width | None available | -b/--byte | None available | --gap-fill | None available | --pad-to | None available | --set-start | None available | --change-start | None available | --adjust-start | None available | --change-addresses | None available | --adjust-vma | None available | --change-section-address | None available | --adjust-section-vma | None available | --change-section-lma | None available | --change-section-vma | None available | --[no-]change-warnings | None available | --[no-]adjust-warnings | None available | --set-section-flags | None available | Use --rename-section --add-section | --add-section | --rename-section | --rename-section | --long-section-names | None available | COFF only --change-leading-char | None available | --remove-leading-char | None available | --reverse-bytes | None available | --redefine-sym | --redefine-sym | --redefine-syms | None available | --srec-len | None available | --srec-forceS3 | None available | --strip-symbols | None available | --strip-unneeded-symbols | None available | --keep-symbols | None available | --localize-symbols | None available | --globalize-symbols | None available | --keep-global-symbols | --keep-global-symbols | --weaken-symbols | None available | --alt-machine-code | None available | --writable-text | None available | --readonly-text | None available | --pure | None available | --impure | None available | --prefix-symbols | --prefix-symbols | --prefix-sections | None available | --prefix-alloc-sections | None available | --file-alignment | None available | --heap | None available | --image-base | None available | --section-alignment | None available | --stack | None available | --subsystem | None available | --compress-debug-sections | --compress-debug-sections | --decompress-debug-sections| --decompress-debug-sections| --verbose | None available | objcopy @ | None available |

On Mon, 22 Oct 2018 at 11:00, James Henderson <jh7370.2008 at my.bristol.ac.uk> wrote:

Hi,

On Thursday of the recent developers meeting, we had a round-table discussing llvm-objcopy. Below are some notes I took from that meeting. The discussion was fairly free-flowing, so the notes are not particularly in depth. If anybody has any other comments relating to this meeting, feel free to add to this! Feature request: converting from 32-bit ELF to 64-bit ELF: -- Size in sections broken, needs updating to not just be a public member variable. Making llvm-objcopy into a library: -- Errors need to be non-fatal (return llvm::Error). -- Would be nice to provide this as a writable portion of libObject. Action: James Henderson to provide results of feature comparison versus GNU objcopy. Multiple file formats: -- Don't try to use a common intermediate representation for all object file formats! -- Separate backends for different file formats. ---- Would like to avoid people "forgetting" to implement some switches when implementing a new backend, leading to silent ignoring of switches (maybe use subclasses etc). ---- Shouldn't need to implement each option, beyond an "unsupported" message or similar. Output should be stable: -- Currently not the case for section header table (is deterministic, but might be unnecessarily different to input). -- No need to go to heroic efforts, if not realistic, or a better alternative is possible. Discussion on being able to modify the program header table: -- Jake reluctant to. -- But if real use case presents itself, should be okay. -- Some requirements to add segments post-link. -- Embedded use-cases may well break the immutable program header table requirement. File bugs upstream for visibility: -- Action: Jake Ehrlich to request himself, James Henderson, Jordan Rupprecht, and Alexander Shaposhnikov (four current main upstream developers/reviewers of llvm-objcopy) added as default-CC for llvm-objcopy bugs. Compatibility with GNU objcopy is a top concern: -- Where diverged, believed that GNU behaviour doesn't make sense, but open to alternative. -- File bugs/propose changes if issues encountered. Regards, James -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20181022/4116bee6/attachment.html> -------------- next part -------------- A non-text attachment was scrubbed... Name: ObjcopyFeatureAnalysis.xlsx Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet Size: 11227 bytes Desc: not available URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20181022/4116bee6/attachment.xlsx>

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