Re: [Qemu-devel] Single stepping & GDB on ARM

[Richard Henderson <rth@twiddle.net>]

On 09/17/2013 03:02 AM, Emmanuel Blot wrote:
> There is a piece of code I'm not sure to understand, in
>    get_page_addr_code(CPUArchState *env1, target_ulong addr)
> 
> …
>     if (unlikely(env1->tlb_table[mmu_idx][page_index].addr_code !=
>                  (addr & TARGET_PAGE_MASK))) {
>         cpu_ldub_code(env1, addr);
>     }
>     pd = env1->iotlb[mmu_idx][page_index] & ~TARGET_PAGE_MASK;
>     mr = iotlb_to_region(pd);
>     if (memory_region_is_unassigned(mr))
> …
> 
> cpu_ldub_code() leads to call io_mem_read() which may trigger a
> unassigned_mem_read().
> In this case, the invalid mem access is always considered as a data
> access, whereas it is an execution access if I'm not mistaken.
> 
> In other words, before
> get_page_addr_code:memory_region_is_unassigned() is tested and
> get_page_addr_code:do_unassigned_access() gets a "chance" to be called
> as an "instruction" invalid access, another unsigned access is
> triggered with a "data" invalid access.
> 
> Did I miss something here?

No miss.  That cpu_ldub_code ought to be just a straight tlb fill,
rather than a read with discarded result.  E.g. the

  tlb_fill(env, addr, READ_ACCESS_TYPE, mmu_idx, retaddr);

line from exec/softmmu_template.h.


r~