linux-kernel - Re: [PATCH 16/20] ARC: entry: Add more common chores to EXCEPTION

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Date:   Fri, 18 Aug 2023 16:56:52 +0400
From:   Pavel.Kozlov@...opsys.com
To:     Vineet Gupta <vgupta@...nel.org>,
        linux-snps-arc@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org,
        Shahab Vahedi <Shahab.Vahedi@...opsys.com>,
        Alexey Brodkin <Alexey.Brodkin@...opsys.com>
Subject: Re: [PATCH 16/20] ARC: entry: Add more common chores to EXCEPTION_PROLOGUE

Hi Vineet,

> Subject: [PATCH 16/20] ARC: entry: Add more common chores to
>         EXCEPTION_PROLOGUE
> 
> THe high level structure of most ARC exception handlers is
>  1. save regfile with EXCEPTION_PROLOGUE
>  2. setup r0: EFA (not part of pt_regs)
>  3. setup r1: pointer to pt_regs (SP)
>  4. drop down to pure kernel mode (from exception)
>  5. call the Linux "C" handler
> 
> Remove the boiler plate code by moving #2, #3, #4 into #1.
> 
> The exceptions to most exceptions are syscall Trap and Machine check
> which don't do some of above for various reasons, so call a newly
> introduced variant EXCEPTION_PROLOGUE_KEEP_AE (same as original
> EXCEPTION_PROLOGUE)

I'm observing the ARC700 (nSIM) system freeze after this patch.

...
f0000000.serial: ttyS0 at MMIO 0xf0000000 (irq = 24, base_baud = 3125000) is a 16550A
printk: console [ttyS0] enabled
printk: console [ttyS0] enabled
printk: bootconsole [uart8250] disabled
printk: bootconsole [uart8250] disabled
NET: Registered PF_PACKET protocol family
NET: Registered PF_KEY protocol family
clk: Disabling unused clocks
Freeing unused kernel image (initmem) memory: 2856K
This architecture does not have kernel memory protection.
Run /init as init process

> @@ -128,11 +123,6 @@ ENTRY(EV_PrivilegeV)
> 
>          EXCEPTION_PROLOGUE
> 
> -       lr  r0, [efa]
> -       mov r1, sp
> -
> -       FAKE_RET_FROM_EXCPN
> -
>          bl  do_privilege_fault
>          b   ret_from_exception

The same update is also required for the call_do_page_fault wrapper for ARcompact. 

Regards,
Pavel