Re: [PATCH V5 13/21] riscv: compat: process: Add UXL_32 support in start_thread

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On Tue, 01 Feb 2022 07:05:37 PST (-0800), guoren@xxxxxxxxxx wrote:
From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>

If the current task is in COMPAT mode, set SR_UXL_32 in status for
returning userspace. We need CONFIG _COMPAT to prevent compiling
errors with rv32 defconfig.

Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
---
 arch/riscv/kernel/process.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 03ac3aa611f5..1a666ad299b4 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -97,6 +97,11 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
 	}
 	regs->epc = pc;
 	regs->sp = sp;
+
+#ifdef CONFIG_COMPAT
+	if (is_compat_task())
+		regs->status |= SR_UXL_32;

Not sure if I'm just misunderstanding the bit ops here, but aren't we trying to set the UXL field to 1 (for UXL=32)? That should be a bit field set op, not just an OR.

+#endif
 }

 void flush_thread(void)

Additionally: this isn't really an issue so much with this patch, but it does bring up that we're relying on someone else to have set UXL=64 on CONFIG_COMPAT=n systems. I don't see that in any spec anywhere, so we should really be setting UXL in Linux for all systems (ie, not just those with
COMPAT=y).



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