In order to specify a build correctly, all input to each step needs to be considered in determining whether the step’s output is up to date. For linker input other than object files and libraries, there doesn’t appear to be any way to make GN aware that a dependency exists.

This happens when the linker uses additional input in the form of an exported symbols file, for example. https://chromium-review.googlesource.com/c/crashpad/crashpad/+/833408/3/snapshot/BUILD.gn#249 is an instance of this. elf/elf_image_reader_test.cc in the snapshot_test target requires an exported symbols list, which is presented to the linker via -Wl,--dynamic-list,elf/test_exported_symbols.sym. There’s no way to tell the linker that elf/test_exported_symbols.sym is relevant to the link step. If only elf/test_exported_symbols.sym changes, the library will not be relinked.

As a workaround, it’s possible to specify elf/test_exported_symbols.sym in “inputs”. Unfortunately, this isn’t quite as targeted as appropriate. With this, the entire target depends on the input, so not only will it be relinked if elf/test_exported_symbols.sym changes, each source file in the target will also be recompiled. This is not necessary, because there’s no true dependency relationship between compilation and this file, it’s strictly relevant to the link step. Furthermore, because of  bug 781858 , “inputs” have no effect in a “config”, so in this example, elf/test_exported_symbols.sym can change and nothing will be rebuilt. The build is incorrectly specified, and I can’t see a way to fix it.

https://chromium-review.googlesource.com/c/crashpad/crashpad/+/833408/3/tools/BUILD.gn#72 is another example. Here, the linker needs “-sectcreate __TEXT __info_plist mac/sectaskaccess_info.plist. The “inputs” do have an effect here because they’re written directly into the target, not into a config, so now, when mac/sectaskaccess_info.plist changes, not only is generate_dump relinked, but generate_dump.cc is also recompiled. The same thing happens in the exception_port_tool target. (In fact, it’d be better if the two shared a config, but  bug 781858  disallows “inputs” from working properly.)