On 22/09/17 15:00, Mike Looijmans wrote:
I think this remark in the referenced link is the best summary of "what
could be improved":
"""the biggest weakness of the sstate signature bits, in my opinion, is
that it only tracks inputs, not outputs. If task A depends on B, and the
metadata input to B changes, then A will be rebuilt, even if the
*output* of B didn't change as a result of the change to its metadata."""
For example, if someone fixes a bug in gcc that only applies to MIPS,
then builds that only target an ARM machine shouldn't be affected. Much
worse than that, I have a dependency like:
gcc -> ... -> python -> bitstream tool -> FPGA image
so this means that a change in gcc causes Python to rebuild, which
causes the bitstream tool to be rebuilt and produce idential output, and
that triggers a roughly 31-hour build of lots of FPGA images. These are
the ones we really want to break. A binary output compare would help a
lot, even if 80% of the libraries fail to create reproducible output, I
may still be spared those 31 hours...
I think tracking digital output is technically feasible, and won't
require any change to existing recipes.
Also think about "feed" setups. When I see my settop reporting "331
packages need updating"... It'd be great if that could be avoided.
That's what packagefeed-stability.bbclass is for. Work on binary
reproducibility will improve things here too.
Joshua
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