Re: [PATCH 0/2] target/arm: Improve M-profile exception logging

["Philippe Mathieu-Daudé" <philippe.mathieu.daude@gmail.com>]

On 15/3/22 21:43, Peter Maydell wrote:
> Our current logging for M-profile exceptions has a couple of holes
> which are particularly confusing for the case of an exception taken
> immediately out of reset:
>   * we don't log the initial PC/SP loaded from the vector table
>   * we don't log the PC we load from the vector table when
>     we take an exception
>   * we don't log the address for i-side aborts
> 
> This case is quite common where the user has failed to provide a
> vector table in their ELF file and QEMU thus loads garbage for the
> initial PC. At the moment the logging looks like:
> 
> $ qemu-system-arm [...] -d in_asm,cpu,exec,int
> Taking exception 3 [Prefetch Abort] on CPU 0
> ...with CFSR.IACCVIOL
> ...BusFault with BFSR.STKERR
> ...taking pending nonsecure exception 3
> ----------------
> IN:
> 0x20000558:  08000079  stmdaeq  r0, {r0, r3, r4, r5, r6}
> 
> 
> After this patchset it looks like:
> 
> $ qemu-system-arm [...] -d in_asm,cpu,exec,int
> Loaded reset SP 0x0 PC 0x0 from vector table
> Loaded reset SP 0xd008f8df PC 0xf000bf00 from vector table
> Taking exception 3 [Prefetch Abort] on CPU 0
> ...at fault address 0xf000bf00
> ...with CFSR.IACCVIOL
> ...BusFault with BFSR.STKERR
> ...taking pending nonsecure exception 3
> ...loading from element 3 of non-secure vector table at 0xc
> ...loaded new PC 0x20000558
> ----------------
> IN:
> 0x20000558:  08000079  stmdaeq  r0, {r0, r3, r4, r5, r6}
> 
> and I think it is somewhat clearer that we loaded a bogus
> PC from the vector table at reset, faulted at that address,
> loaded the HardFault entry point which was bogus but at
> least readable, and started executing code from there.
> 
> The double-logging of the reset loads is the result of
> the way we currently reset the CPU twice on QEMU startup.
> If we ever manage to fix that silliness it'll go away.
> 
> 
> (Patchset inspired by a stackexchange question:
> https://stackoverflow.com/questions/71486314/loading-an-elf-file-into-qemu
> )
> 
> thanks
> -- PMM
> 
> Peter Maydell (2):
>    target/arm: Log M-profile vector table accesses
>    target/arm: Log fault address for M-profile faults

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>