Re: [PATCH V2] riscv: set trap vector earlier

From: Alexandre Ghiti
Date: Tue May 07 2024 - 01:29:16 EST


Hi Yang,

On 06/05/2024 04:22, yang.zhang wrote:
From: "yang.zhang" <yang.zhang@xxxxxxxxxxxx>

If trap earlier, trap vector doesn't yet set properly, current
value maybe set by previous firmwire, typically it's the _start of kernel,
it's confused and difficult to debuge, so set it earlier.


What about:

"The exception vector of the booting hart is not set before enabling the mmu and then still points to the value of the previous firmware, typically _start_kernel. That makes it hard to debug setup_vm() when bad things happen. So fix that by setting the exception vector earlier."


---
v1 -> v2:
As Alex commented, remove the patch for supporting hugesize kernek image
Add the omissive logic of set trap vector earlier

Signed-off-by: yang.zhang <yang.zhang@xxxxxxxxxxxx>
---
arch/riscv/kernel/head.S | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index 4236a69c35cb..03dc440e643e 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -300,6 +300,9 @@ SYM_CODE_START(_start_kernel)
#else
mv a0, a1
#endif /* CONFIG_BUILTIN_DTB */
+ /* Set trap vector to spin forever to help debug */
+ la a3, .Lsecondary_park
+ csrw CSR_TVEC, a3
call setup_vm
#ifdef CONFIG_MMU
la a0, early_pg_dir

Note that this patch will allow to catch any exception happening in setup_vm() but as we reset stvec in relocate_enable_mmu. But that's ok, it will help catching weird bugs more easily :)

With the commit message fixed, you can add:

Reviewed-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>

Thanks,

Alex