8000 Fix kernel stack pointer save on LoongArch64 (again) by AsakuraMizu · Pull Request #14 · arceos-org/axcpu · GitHub
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Fix kernel stack pointer save on LoongArch64 (again) #14

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Merged
merged 1 commit into from
Jul 15, 2025
Merged

Fix kernel stack pointer save on LoongArch64 (again) #14

merged 1 commit into from
Jul 15, 2025

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AsakuraMizu
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Description

The fix proposed previously at 7152ea5 is wrong. next_ctx.sp, which is saved in the previous context_switch, is never the top of kernel stack.

This PR fixs this by porting oscomp/arceos#18.

Comparison

As said in arceos-org/arceos#229, the previous fix tried to take a similar approach to x86_64. But x86_64's TaskContext has a fixed kstack_top field, so this is correct.

I believe there is no need to reduce the times to save kernel sp on LoongArch64 since on x86_64 each save and load involves a memory operation but here we just read and write registers, which is the same way sscratch is used on RISC-V.

@equation314
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next_ctx.sp, which is saved in the previous context_switch, is never the top of kernel stack.

What does this mean? The sp field in TaskContext is set to the top of kernel stack during initialization and will not be modified.

TaskContext has a fixed kstack_top field, so this is correct.

You mean the sp field in TaskContext is not fixed?

@AsakuraMizu
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The sp field in TaskContext is set to the top of kernel stack during initialization and will not be modified.

It will be modified here:

axcpu/src/aarch64/context.rs

Lines 186 to 188 in 92fd534

mov x19, sp
mrs x20, tpidr_el0
stp x19, x20, [x0]

@equation314
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You are right, I confused sp with the top of kernel stack.

@equation314 equation314 merged commit d2544fe into arceos-org:main Jul 15, 2025
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@AsakuraMizu AsakuraMizu deleted the fix/la-ksp branch July 16, 2025 06:48
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@AsakuraMizu @equation314
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