[llvm-dev] [RFC] better link error messages
Hal Finkel via llvm-dev
llvm-dev at lists.llvm.org
Sat Mar 25 06:56:04 PDT 2017
On 03/24/2017 11:42 PM, Sean Silva via llvm-dev wrote:
>
>
> On Mar 24, 2017 5:22 PM, "Reid Kleckner" <rnk at google.com
> <mailto:rnk at google.com>> wrote:
>
> I figured you might consider moving the basenames of the filename
> earlier in the diagnostic, something like:
>
> bin/ld.lld: *error:* duplicate symbol:
> lld::elf::MipsGotSection::addEntry(lld::elf::SymbolBody&, long,
> lld::elf::RelExpr)
> *>>> defined at* Writer.cpp:38 in
> /home/buildslave/buildslave/clang-cmake-aarch64-39vma/llvm/tools/lld/ELF/
> *>>>* Writer.cpp.o in archive lib/liblldELF.a
> *>>> defined at* SyntheticSections.cpp:673 in
> /home/buildslave/buildslave/clang-cmake-aarch64-39vma/llvm/tools/lld/ELF/
> *>>>* SyntheticSections.cpp.o in archive lib/liblldELF.a
>
Please don't do this (split the base name from the path). Tools that
match file names, grep, etc. won't be able to locate the files easily.
I've worked with projects that, especially when all library dependencies
are included, have lots of files with generic names (e.g. Writer.cpp).
This is convenient for relatively self-contained projects where you can
recognize the file names. We work on one such project. This is not the
general case.
If you'd like to make the base name easier to visually differentiate, I
recommend just repeating it:
bin/ld.lld: *error:* duplicate symbol:
lld::elf::MipsGotSection::addEntry(lld::elf::SymbolBody&, long,
lld::elf::RelExpr)
*>>> defined at* Writer.cpp:38
(/home/buildslave/buildslave/clang-cmake-aarch64-39vma/llvm/tools/lld/ELF/Writer.cpp:38)
*>>>* Writer.cpp.o in archive lib/liblldELF.a
*>>> defined at* SyntheticSections.cpp:673
(/home/buildslave/buildslave/clang-cmake-aarch64-39vma/llvm/tools/lld/ELF/SyntheticSections.cpp:673)
*>>>* SyntheticSections.cpp.o in archive lib/liblldELF.a
I'd be happy with that.
Thanks again,
Hal
>
> Oftentimes filenames are unique enough that it tells you where to
> go immediately. Maybe it's a bad idea for the source location
> info, though. You want that to be copy-pastable or clickable in an
> IDE.
>
>
> I really like this.
>
> I'm on mobile right now which is a worst case, but this is pretty
> readable even there. I've attached a screenshot. One nit is that we
> want it to be clear that Writer.cpp.o is in an archive before reading
> "Writer.cpp.o". Maybe something like "archive member Writer.cpp.o in ...".
>
> I also think we might want some bold text for the input file lines to
> clarify better what they are. Maybe ">>> *from* *input* *file*:
> archive member ..." instead of just a blank ">>> archive member ..."
>
> -- Sean Silva
>
>
> On Fri, Mar 24, 2017 at 4:07 PM, Rui Ueyama via llvm-dev
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>
> On Fri, Mar 24, 2017 at 2:04 PM, Sean Silva
> <chisophugis at gmail.com <mailto:chisophugis at gmail.com>> wrote:
>
> I lile the idea of having it more structured and I think
> your suggested format is the right direction.
>
> I think one principle should be that we assume that file
> names and symbol names are "really long" (possibly wrapped
> by the terminal etc.).
>
>
> Right. That's what we should expect.
>
> I believe the current error message format for the existing
> linkers were set more than 30 years ago when path names and
> symbol names were much shorter than they are today. If they
> are short, error messages become something like
> "src/libfoo/bar.o: undefined symbol: strbar", which is quite
> easy to read. That is unfortunately no longer the case because
> we are creating significantly larger programs than a few
> decades ago and C++ name mangling makes symbol names
> significantly longer than before.
>
> So I would modify your suggested format to use the "note"
> color for the strings like "Object 1" so that even if
> those lines are wrapped by the terminal then they can
> still be easily visually parsed. We may also want to do
> something like ">>> Object 1:" so that places without
> color (like google's internal web ui for build logs, or if
> users are piping the build system's output into `less` or
> `tee`) are still a bit easier to parse in the presence of
> wrapped lines.
>
>
> Makes sense. I tried a few different formats based on
> suggestions from Mehdi, Hans and you, and come up with this
> one. What do you think?
>
> bin/ld.lld: *error:* undefined symbol:
> lld::elf::EhFrameSection<llvm::object::ELFType<(llvm::support::endianness)0,
> true> >::addSection(lld::elf::InputSectionBase*)
> *>>> referenced by*
> /home/buildslave/buildslave/clang-cmake-aarch64-39vma/llvm/tools/lld/ELF/Writer.cpp:207
> *>>>* lib/liblldELF.a(Writer.cpp.o)
>
>
> bin/ld.lld: *error:* duplicate symbol:
> lld::elf::MipsGotSection::addEntry(lld::elf::SymbolBody&,
> long, lld::elf::RelExpr)
> *>>> defined at*
> /home/buildslave/buildslave/clang-cmake-aarch64-39vma/llvm/tools/lld/ELF/Writer.cpp:38
> *>>>* lib/liblldELF.a(Writer.cpp.o)
> *>>> defined at*
> /home/buildslave/buildslave/clang-cmake-aarch64-39vma/llvm/tools/lld/ELF/SyntheticSections.cpp:673
> *>>>* lib/liblldELF.a(SyntheticSections.cpp.o)
>
>
> This format prints out source file names and object file names
> in different lines. I found that that is easier to read than
> print them in the same line, as error messages with some
> amount of whitespace are easier to find in dense build system
> outputs.
>
> This principle also suggests (and your suggested format
> does this) that to avoid having to parse past a
> symbol/file name to get to other information, there should
> be at most one symbol/file name on a given line and there
> should never be anything after it on the line. The ld64
> format violates this, for example.
>
> -- Sean Silva
>
> On Mar 23, 2017 4:18 PM, "Rui Ueyama via llvm-dev"
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>
> wrote:
>
> Folks,
>
> I'd like propose a new error message format for LLD so
> that error message for undefined or duplicated symbols
> are more informative and easy to read.
>
> Below are examples of the current error messages (note
> that characters in red are actually red on terminal):
>
> *Undefined symbols*
> /ssd/clang/bin/ld.lld: error:
> /ssd/llvm-project/lld/ELF/Writer.cpp:207:
> undefined symbol
> 'lld::elf::EhFrameSection<llvm::object::ELFType<(llvm::support::endianness)0,
> true> >::addSection(lld::elf::InputSectionBase*)'
>
> *Conflicting symbols*
> /ssd/clang/bin/ld.lld: error:
> /ssd/llvm-project/lld/ELF/Writer.cpp:38: duplicate
> symbol
> 'lld::elf::MipsGotSection::addEntry(lld::elf::SymbolBody&,
> long, lld::elf::RelExpr)'
> /ssd/clang/bin/ld.lld: error:
> /ssd/llvm-project/lld/ELF/SyntheticSections.cpp:673:
> previous definition was here
>
>
> For each error, we want to print out information about
> 1) symbol name, 2) source file name(s) and source
> location(s) if available and 3) source object file
> name(s) and archive file name(s) if available.
> Currently, these messages lack object file names, and
> I think the above error messages are a bit hard to
> grasp because too much information is packed into each
> line.
>
> I'm thinking of changing the format to something like
> the following:
>
> *Undefined symbols*
> /ssd/clang/bin/ld.lld: error: undefined symbol:
> lld::elf::EhFrameSection<llvm::object::ELFType<(llvm::support::endianness)0,
> true> >::addSection(lld::elf::InputSectionBase*)
> Source: /ssd/llvm-project/lld/ELF/Writer.cpp:207
> Object: lib/liblldELF.a(Writer.cpp.o)
>
> *Conflicting symbols*
> /ssd/clang/bin/ld.lld: error: duplicate symbol:
> lld::elf::MipsGotSection::addEntry(lld::elf::SymbolBody&,
> long, lld::elf::RelExpr)
> Source 1: /ssd/llvm-project/lld/ELF/Writer.cpp:38
> Source 2:
> /ssd/llvm-project/lld/ELF/SyntheticSections.cpp:673
> Object 1: lib/liblldELF.a(Writer.cpp.o)
> Object 2 : lib/liblldELF.a(SyntheticSections.cpp.o)
>
>
> The new error messages contain complete information
> that the linker is able to gather, and it uses more
> vertical space to improve readability.
>
> Thoughts?
>
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--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory
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