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Clear Cache before VBR call in default demo. #256

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terriblefire opened this issue Mar 21, 2024 · 1 comment · May be fixed by #267
Open

Clear Cache before VBR call in default demo. #256

terriblefire opened this issue Mar 21, 2024 · 1 comment · May be fixed by #267

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@terriblefire
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terriblefire commented Mar 21, 2024 •
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In your awesome example code, the code to get the VBR will crash on an 060 with Caches enabled because the data you specify as the instructions to execute in supervisor mode will never actually be written to ram. Its held purely on the stack (and in cache)

Please add...

CacheClearU();

immediately before

vbr = (APTR)Supervisor((ULONG (*)())getvbr);

and code will run even with 060 MMU+Caches enabled.
@terriblefire
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I guess another way to do it would be to declare it globally rather than as a local variable.

@yupferris yupferris mentioned this issue Dec 17, 2024
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yupferris added a commit to yupferris/vscode-amiga-debug that referenced this issue Dec 17, 2024
@yupferris
template: Fix GetVBR for systems with caches enabled
affac22 
Previously, the supervisor portion of `GetVBR` would be copied to the stack, but without then clearing caches, there would be no guarantee that the instruction cache would contain this data (it's most likely dirty in the data cache and not yet committed to memory). On my setup (060 fpu+mmu), this would consistently crash.

So, let's rewrite this code as inline asm in a function, which is cleaner (no more raw data words), avoids the unnecessary copy (to initialize a local variable which isn't actually required), and avoids an unnecessary cache clear (which would also work around the issue, but in an expensive way).

Fixes BartmanAbyss#256.
@yupferris yupferris linked a pull request Dec 17, 2024 that will close this issue
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template: Fix GetVBR for systems with caches enabled yupferris/vscode-amiga-debug
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@terriblefire