riscv: refine vector context layout on stack

[Saiiijchan]

Currently, vector registers are not placed continuously in the stack. Place v31 - v0 in order from high address to low address to facilitate debugger analysis of task stack context.

Vector general register layout:

Before:
+--------------+ <-- High Address
| v7 |
+--------------+
| v6 |
+--------------+
| ... |
+--------------+
| v0 |
+--------------+ <-- v0 - v7
| v15 |
+--------------+
| v14 |
+--------------+
| ... |
+--------------+
| v8 |
+--------------+ <-- v8 - v15
| ... |
+--------------+
| v24 |
+--------------+ <-- Low address

After:
+--------------+ <-- High Address
| v31 |
+--------------+
| v30 |
+--------------+
| ... |
+--------------+
| v1 |
+--------------+
| v0 |
+--------------+ <-- Low Address

Description

Test Steps

Checklist:

• I have tested my changes. No regression in existing tests.
• I have modified and/or added unit-tests to cover the code changes in this Pull Request.

Related Issue

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[aggarg]

facilitate debugger analysis of task stack context.

@Saiiijchan Would you please help us understand how does this change facilitate debugger analysis of task stack context?

[Saiiijchan]

facilitate debugger analysis of task stack context.

@Saiiijchan Would you please help us understand how does this change facilitate debugger analysis of task stack context?

Our debugger team is developing a GDB tool for FreeRTOS that can parse the task context from the stack. It would be easier to implement if the registers were arranged sequentially.

[aggarg]

@Saiiijchan Thank you for sharing!

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[aggarg]

@Saiiijchan I made a change to change the mstatus location in the context. I think it should not have any impact on this change, would you please double confirm that your change still works?

[Saiiijchan]

@aggarg I tested and no problems. However, there are not additional regs on my platfrom.

[aggarg]

@Saiiijchan Thank you for confirming!