Author Topic: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited) (Read 20223 times)

chief1983 · **Reply #40 on:** December 01, 2019, 10:35:14 pm

Well the good news is the performance gain alone may be enough incentive for a mass effort to fix all the old models floating around.

ShivanSpS · **Reply #41 on:** December 01, 2019, 10:42:15 pm

That is on ARM, i dont think x86 will have any performance gain im afraid. But i will check just to be sure.

At any rate, ARM is becoming more and more powerfull and common.

ShivanSpS · **Reply #42 on:** December 02, 2019, 10:43:07 am

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taylor · **Reply #43 on:** December 02, 2019, 11:28:52 am

ARM is little endian so that code is unused in this case. But yeah, that 1 byte at the start is

. Even if that swapping code is unused, that 1 byte means the shield collision data is going to be unaligned.

INTEL_INT/INTEL_FLOAT are for byte swapping.

ShivanSpS · **Reply #44 on:** December 02, 2019, 11:50:35 am

Then disabling SLDC data loading on archs that are not x86 is the way to go, because the workaround i came out with in fvi.cpp with all those memcpy that are done at every shild hit is in no way faster and fixing SLDC for non x86 archs would mean having to do it again, chaging that char for an int, making models incompatible.

Maybe there is some other way, but no other comes to mind right now. Dealing with it would need to do an unaligned access at some point or the other, that you can never be sure that the kernel is going to be able to fix or not.

Now if i can only figure out what bit of data is causing the release build to crash at model load on bsp_collide_tree...

Goober5000 · **Reply #45 on:** December 02, 2019, 04:51:26 pm

Why would the model alignment affect FPS? Aren't models completely loaded into memory before the mission starts? So during the mission they should be referenced from their FSO data structure, not from the POF file.

ShivanSpS · **Reply #46 on:** December 02, 2019, 05:58:12 pm

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Col. Fishguts · **Reply #47 on:** December 03, 2019, 05:10:17 am

Quote from: ShivanSpS on December 02, 2019, 11:50:35 am

Maybe there is some other way, but no other comes to mind right now. Dealing with it would need to do an unaligned access at some point or the other, that you can never be sure that the kernel is going to be able to fix or not.

This thread triggers PTSD flashbacks from when I was trying to get a Doom sourceport working on a Sparc workstation (sparc64 doesn't take a performance hit with unaligned memory access, it just goes lolnope SIGBUS).

Unaligned POF data needs to be fixed externally, but the unaligned structs in FSO code you should be able to fix by telling gcc to enforce alignment during compile time:

https://gcc.gnu.org/onlinedocs/gcc-3.1/gcc/Type-Attributes.html

Sprinkle in "__attribute__ ((aligned (4)))"
(or 8) where needed.

I know other compilers (like the Sun CC) have command line flags to enforce that globally during compilation, but gcc seems to be missing such a feature?

ShivanSpS · **Reply #48 on:** December 03, 2019, 07:33:28 am

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ShivanSpS · **Reply #49 on:** December 03, 2019, 07:57:16 pm

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ShivanSpS · **Reply #50 on:** December 04, 2019, 07:14:45 pm

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Goober5000 · **Reply #51 on:** December 04, 2019, 09:10:25 pm

This is part of the scripting system. There have been several fixes to that over the years; it's entirely possible that this is related. See these PRs for example:
https://github.com/scp-fs2open/fs2open.github.com/pull/2119
https://github.com/scp-fs2open/fs2open.github.com/pull/1960

You may be stuck with coding up an alignment-fixer-loader, unless you want to be restricted to only a subset of mods. There are literally thousands of POFs that have been released for FreeSpace -- perhaps tens of thousands -- and it would be impractical to fix them all.

chief1983 · **Reply #52 on:** December 04, 2019, 09:36:59 pm

Perhaps, but starting with ones released on Knossos would be a big win and a much smaller subset.

ShivanSpS · **Reply #53 on:** December 04, 2019, 10:00:50 pm

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ShivanSpS · **Reply #54 on:** December 05, 2019, 09:13:25 pm

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ShivanSpS · **Reply #55 on:** December 08, 2019, 08:23:22 pm

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chief1983 · **Reply #56 on:** December 08, 2019, 08:25:48 pm

I wonder if we could integrate this conversion into knossos/nebula if it ever gets stable enough...

ShivanSpS · **Reply #57 on:** December 08, 2019, 08:52:42 pm

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ShivanSpS · **Reply #58 on:** December 09, 2019, 05:45:08 pm

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chief1983 · **Reply #59 on:** December 09, 2019, 05:47:35 pm

Just compile it default disabled on ARM maybe. Just like SLDC. Solved!

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Author Topic: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited) (Read 20223 times)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)

Re: [3.7.2-ARM] Unaligned Memory Access at modeloctant.cpp:28 (title edited)