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

Shile Zhang
2019-11-15T09:43:54Z

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.