On Mon, 5 Sep 2022 12:29:16 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> So looking at the first line:
>
> __entry->pfn != -1UL ? pfn_to_page(__entry->pfn) : NULL,
>
> The pfn_to_page() must be a macro expanded to that huge output.
>
> The thing is, there's no way that user space can know what the result of
> that pfn_to_page is, as that information is hidden inside the kernel.
>
> I do not see that expanding like the above in the latest kernel. I'm
> guessing the kernel you have has that crazy expansion of pfn_to_page() though.
>
> Probably the best thing that user space can do is to just do what it does
> now and simply output the event fields. We do not want to have the output
> showing all that builtin_constant_p() and size_of() callers.
Yeah, on 5.14 it looks like this:
#define pfn_to_page __pfn_to_page
#define __pfn_to_page(pfn) (vmemmap + (pfn))
#define vmemmap ((struct page *)VMEMMAP_START - (memstart_addr >> PAGE_SHIFT))
#define VMEMMAP_START (-(UL(1) << (VA_BITS - VMEMMAP_SHIFT)))
#define VA_BITS (CONFIG_ARM64_VA_BITS)
#define VMEMMAP_SHIFT (PAGE_SHIFT - STRUCT_PAGE_MAX_SHIFT)
#define PAGE_SHIFT CONFIG_ARM64_PAGE_SHIFT
#define STRUCT_PAGE_MAX_SHIFT (order_base_2(sizeof(struct page)))
#define order_base_2(n) \
( \
__builtin_constant_p(n) ? ( \
((n) == 0 || (n) == 1) ? 0 : \
ilog2((n) - 1) + 1) : \
__order_base_2(n) \
)
#define ilog2(n) \
( \
__builtin_constant_p(n) ? \
((n) < 2 ? 0 : \
63 - __builtin_clzll(n)) : \
(sizeof(n) <= 4) ? \
__ilog2_u32(n) : \
__ilog2_u64(n) \
)
and so on.
Thus, the pfn_to_page() macro gets expanded to some God awful expression.
There's not much we can do about this from the libtraceevent perspective :-/
-- Steve
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