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Surely they could use a disassembler and from that (and monitoring the i/o of a live system) infer a test suite from which they could rebuild the API. The new s

Surely they could use a disassembler and from that (and monitoring the i/o of a live system) infer a test suite from which they could rebuild the API. The new system could be tested to have the same outputs of the live system, and eventually swapped in, fixing bugs and making it more reliable in the process. But I guess that was more expensive than the FPGA emulator

richwater 5y ago
When you have government representatives that don't understand technology, it doesn't get funded. It's no wonder everything is emulated/old/never-replaced.
- h0l0cube 5y ago
  In defense of government, they need to have an audit trail and (in functioning democracies) can be held accountable when things go seriously wrong, so it means they only have a select few orgs to choose from that have passed all the certifications/due diligence. Connex (the company running the show at the time) were a private operator who has lease of the rail system for probably long enough to justify modernizing some of the systems, but maybe not enough to justify a full rewrite. Rewrites of systems with big safety implications, like civil transport, would have a different risk profile to upgrades of less consequential legacy systems Edit: Apparently it did eventually get replaced https://news.ycombinator.com/item?id=29158255 https://news.ycombinator.com/item?id=29158255
ajxs 5y ago
Reverse-engineering of even simple binaries tends to be difficult enough, without the stakes being as high as the program safely running the train control system of a major city. I can't pretend to know what conditions this was originally engineered under, but these kind of systems today are subject to intensely rigorous testing, and sometimes formal analysis. In a safety-critical system it's just not going to be worth doing that. Plus, if the original source code has been misplaced, the original requirement documents are probably gone too.
- h0l0cube 5y ago
  I sort-of kind-of agree with this. It is certainly why most of these systems aren't worth upgrading. But reasons why it might be desirable to wear this cost is if the original system is already showing signs of bugs, which may be true if it's being operated in new conditions (e.g., interop with new systems, increasing workload), or there are safety features that could be added but not without refactoring. But, yes, if it ain't broke, surely there's no need to fix it Edit: Also worth pointing out that formal verification was likely not a component of building the original software, and it likely has bugs it's kept since inception. Updating the API to a language more conducive to formal verification might be an option that improves safety over the legacy system Edit: Apparently they did replace it all eventually https://news.ycombinator.com/item?id=29158255 https://news.ycombinator.com/item?id=29158255

richwater 5y ago

When you have government representatives that don't understand technology, it doesn't get funded. It's no wonder everything is emulated/old/never-replaced.

h0l0cube 5y ago
In defense of government, they need to have an audit trail and (in functioning democracies) can be held accountable when things go seriously wrong, so it means they only have a select few orgs to choose from that have passed all the certifications/due diligence. Connex (the company running the show at the time) were a private operator who has lease of the rail system for probably long enough to justify modernizing some of the systems, but maybe not enough to justify a full rewrite. Rewrites of systems with big safety implications, like civil transport, would have a different risk profile to upgrades of less consequential legacy systems Edit: Apparently it did eventually get replaced https://news.ycombinator.com/item?id=29158255 https://news.ycombinator.com/item?id=29158255

ajxs 5y ago

Reverse-engineering of even simple binaries tends to be difficult enough, without the stakes being as high as the program safely running the train control system of a major city. I can't pretend to know what conditions this was originally engineered under, but these kind of systems today are subject to intensely rigorous testing, and sometimes formal analysis. In a safety-critical system it's just not going to be worth doing that. Plus, if the original source code has been misplaced, the original requirement documents are probably gone too.

h0l0cube 5y ago
I sort-of kind-of agree with this. It is certainly why most of these systems aren't worth upgrading. But reasons why it might be desirable to wear this cost is if the original system is already showing signs of bugs, which may be true if it's being operated in new conditions (e.g., interop with new systems, increasing workload), or there are safety features that could be added but not without refactoring. But, yes, if it ain't broke, surely there's no need to fix it Edit: Also worth pointing out that formal verification was likely not a component of building the original software, and it likely has bugs it's kept since inception. Updating the API to a language more conducive to formal verification might be an option that improves safety over the legacy system Edit: Apparently they did replace it all eventually https://news.ycombinator.com/item?id=29158255 https://news.ycombinator.com/item?id=29158255