Error handling in SharedCLibrary in ROM
Stuart Swales (8827) 1323 posts |
Before I raise a bug issue, I wonder if someone else could have a gander and see if I’m being an idiot. https://croftnuisk.co.uk/coltsoft-downloads/other/error-bug.zip Tiny C test program which installs a signal handler and raises an error for that to catch (yes, I tried three ways). When it’s compiled and linked with Stubs (DDE 31a) and uses the SharedCLibrary in ROM1, the signal handler is not called as the SharedCLibrary’s own error handler seems to trap. But link the object file with AnsiLib, and the executable behaves as expected. And if SharedCLibrary is RMLoad’ed, the Stubs-linked executable works fine too. 1. Pi 4, RO 5.29 (13 Dec 2022) |
Stuart Swales (8827) 1323 posts |
Oh, it’s been that way for 20 years! [Edit: potentially – see Jeffrey’s reply below] ADD r14, r0, #O_registerDumphas got lumped into just the SASTMhatbroken branch, so on the other branch the regs are just being dumped at the address given by the error number.
https://gitlab.riscosopen.org/RiscOS/Sources/Lib/RISC_OSLib/-/blame/master/kernel/s/k_body#L1614 |
djp (9726) 54 posts |
From RPCEmu *FX0 RISC OS 4.39 (28 Apr 2004) [Kernel 6.80] *help SharedCLibrary ==> Help on keyword SharedCLibrary Module is: C Library 6.15 (21 Sep 2022) *err Aha! An Error: &00000001/1 Ooh Err * *fx0 RISC OS 5.29 (15 Dec 2022) *help sharedclibrary ==> Help on keyword SharedCLibrary Module is: C Library 6.15 (21 Sep 2022) *err Aha! An Error: &00000001/1 Ooh Err * |
Julie Stamp (8365) 467 posts |
I compiled it with cc 5.39 (DDE31) and ran it fine under RO 5.29 (04 Dec 2022).
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Stuart Swales (8827) 1323 posts |
Thanks
I surmise that the RISC OS 5 IOMD target has And RISC OS 4.xx was forked off before the offending implementation. |
Stuart Swales (8827) 1323 posts |
I can’t see a good reason why the error handler in the SCL immediately goes into SVC mode to dump the USR mode registers as it is in USR mode. OK, ‘nowadays’ it needs to load the error number to decide whether to overwrite the current register dump, so it could just lob R14 into one of the unused words of R0-addressed static data, decide whether it is going to dump registers (R0-R13,no-hat) and if so stick the stashed R14 in the register dump. No STM^ / SA bugs to worry about. |
Jeffrey Lee (213) 6048 posts |
The good news is, it looks like the buggy code path would have only been enabled a few months ago, when the SASTMhatbroken switch was rationalised to only be TRUE when targeting older CPUs (previously it was on for all builds). |
Stuart Swales (8827) 1323 posts |
Aha! |
Jean-Michel BRUCK (3009) 333 posts |
Small question, I just did the tests, for the SharedCLibrary it only works if I Rmload this library and unplug the one in ROM. The example of error handling is interesting, on my side I use OSLibSupport. Thanks. |
Stuart Swales (8827) 1323 posts |
The SharedCLibrary that’s in the ROM is optimised for your system (and statically linked to its build location as far as I can tell, so RMFaster is no help to try to patch it). It’s not useful to try to save out the SharedCLibrary (or many other ROM modules these days).
I think OSLibSupport is more for displaying error messages from your application; this particular issue is dealing with the problem of errors returned by the OS to the application via the Error interface. e.g. exceptions raised from the floating point support code will stick their head up and surprise you there! |
Rick Murray (539) 13747 posts |
Somewhere there’s a Gerph hitting his head on the table and mumbling something about tests…
As Stuart says, they’re not identical. While the code is the same, if the target is known then some things can be optimised, different build flags, etc. Plus, since it’s in “ROM”, it can hard link to bits of itself because nothing is expected to move. The latter is something that caught people out back in the day when magazine cover discs used to include frequent CLib updates. I’m of the opinion that a softloaded C Library should refuse to die (just install the new one and reboot), but for whatever reason this was never done. Anyway, the tl;dr is that a ROM build won’t match a softload, even if it claims to be the same. |
Rick Murray (539) 13747 posts |
Yeah, the environment is a bit simplistic at times. When I discovered the borked versions of AcornHTTP, it was because my app was crashing. Perhaps there ought to be some sort of layer in between so the OS can correctly report what raised an important error (especially if it’s in module code) rather than slaughtering whatever the foreground task happens to be…? |
Stuart Swales (8827) 1323 posts |
Perhaps nobody got the memo about not generating errors in non-application module code. I’d go as far as to say the OS ought to detect such things and just bloody well Unplug the miscreant. |
Jeffrey Lee (213) 6048 posts |
Merge request created. https://gitlab.riscosopen.org/RiscOS/Sources/Lib/RISC_OSLib/-/merge_requests/26 |
Stuart Swales (8827) 1323 posts |
Ah, thanks – was just doing something else and about to get round to that! But best done by the Maestro. :-) |
Stuart Swales (8827) 1323 posts |
And the fix is in today’s ROM build – thanks! |
André Timmermans (100) 648 posts |
I don’t know exactly what Gerph implemented in the Select versions of RISC OS to handle background errors but it was nice to see an error box reporting the error and disabling(?) the faulty module/callback/interrupt handler instead of killing of the current foreground application. I know that it involved using some extra bytes near the stack limit to store some context on entry of handlers be able to recover safely to the current foreground task, because AMPlayer’s seeking seemed to corrupt that data. |
Steve Pampling (1551) 8125 posts |
Much (all?) of the error logging and reporting was run through a version of syslog that went somewhat beyond the v0.20 available to non-Select versions of the OS |
Charles Ferguson (8243) 427 posts |
https://www.riscos.com/support/developers/riscos6/diagnostics/backgrounderror.html https://www.riscos.com/support/developers/riscos6/diagnostics/bts.html |