Re: [RFC PATCH v3 6/7] scripts/sorttable: Add ORC unwind tables sort concurrently

[Shile Zhang]

On 2019/11/15 17:07, Peter Zijlstra wrote:
> On Fri, Nov 15, 2019 at 02:47:49PM +0800, Shile Zhang wrote:
>
> > +#if defined(SORTTABLE_64) && defined(UNWINDER_ORC_ENABLED)
> > +/* ORC unwinder only support X86_64 */
> > +#include <errno.h>
> > +#include <pthread.h>
> > +#include <linux/types.h>
> > +
> > +#define ORC_REG_UNDEFINED	0
> > +#define ERRSTRING_MAXSZ		256
> > +
> > +struct orc_entry {
> > +	s16		sp_offset;
> > +	s16		bp_offset;
> > +	unsigned	sp_reg:4;
> > +	unsigned	bp_reg:4;
> > +	unsigned	type:2;
> > +	unsigned	end:1;
> > +} __attribute__((packed));
> > +
> > +struct orctable_info {
> > +	size_t	orc_size;
> > +	size_t	orc_ip_size;
> > +} orctable;
> There's ./arch/x86/include/asm/orc_types.h for this. Please don't
> duplicate. objtool uses that same header.
Good catch! Thanks for your kindly reminder! I'll remove it.
> > +/**
> > + * sort - sort an array of elements
> > + * @base: pointer to data to sort
> > + * @num: number of elements
> > + * @size: size of each element
> > + * @cmp_func: pointer to comparison function
> > + * @swap_func: pointer to swap function
> > + *
> > + * This function does a heapsort on the given array. You may provide a
> > + * swap_func function optimized to your element type.
> > + *
> > + * Sorting time is O(n log n) both on average and worst-case. While
> > + * qsort is about 20% faster on average, it suffers from exploitable
> > + * O(n*n) worst-case behavior and extra memory requirements that make
> > + * it less suitable for kernel use.
> > + *
> > + * This code token out of /lib/sort.c.
> > + */
> > +static void sort(void *base, size_t num, size_t size,
> > +	  int (*cmp_func)(const void *, const void *),
> > +	  void (*swap_func)(void *, void *, int size))
> > +{
> > +	/* pre-scale counters for performance */
> > +	int i = (num/2 - 1) * size, n = num * size, c, r;
> > +
> > +	/* heapify */
> > +	for ( ; i >= 0; i -= size) {
> > +		for (r = i; r * 2 + size < n; r  = c) {
> > +			c = r * 2 + size;
> > +			if (c < n - size &&
> > +					cmp_func(base + c, base + c + size) < 0)
> > +				c += size;
> > +			if (cmp_func(base + r, base + c) >= 0)
> > +				break;
> > +			swap_func(base + r, base + c, size);
> > +		}
> > +	}
> > +
> > +	/* sort */
> > +	for (i = n - size; i > 0; i -= size) {
> > +		swap_func(base, base + i, size);
> > +		for (r = 0; r * 2 + size < i; r = c) {
> > +			c = r * 2 + size;
> > +			if (c < i - size &&
> > +					cmp_func(base + c, base + c + size) < 0)
> > +				c += size;
> > +			if (cmp_func(base + r, base + c) >= 0)
> > +				break;
> > +			swap_func(base + r, base + c, size);
> > +		}
> > +	}
> > +}
> Do we really need to copy the heapsort implementation? That is, why not
> use libc's qsort() ? This is userspace after all.

Yes, I think qsort is better choice than copy-paste here. But qsort does 
not support customized swap func, which is needed for ORC unwind swap 
two tables together.
I think it's hard to do with qsort, so I used sort same with original 
orc unwind table sort.