Re: [PATCH v2] genksyms: Support arm64 CRC32 hardware acceleration1~

["Wentao Guan" <guanwentao@uniontech.com>]

Hello Petr,

> On 5/25/26 3:41 PM, Wentao Guan wrote:
>>> On 5/25/26 10:02 AM, Wentao Guan wrote:
>>>>> Additionally, many distributions already switched to gendwarfksyms last
>>>>> year. Unless someone provides a good reason to keep genksyms around,
>>>>> I expect it will be deprecated soon and eventually removed. It would be
>>>>> more valuable to show whether the same optimization is worthwhile for
>>>>> gendwarfksyms.
>>>> I see gendwarfksyms use crc32 from <zlib.h>, which from zlib1g-dev and zlib1g.
>>>
>>> Ah, I forgot about this, so gendwarfksyms should already be well
>>> optimized. I think that is the most important thing.
>>
>> Which way do you prefer? There are two ways now:
>> 1. this work,
>> 2. import zlib like gendwarfksyms and remove the huge crctab,
>> but need make sure any arch do not cause performance regression?
>> (Assert the user libs precompile with +crc32 is right?)
>> I do some early tests show that:
>> 1) zlib in x86 fast than genksym software
>> 2) zlib in arm64 debian precompile slow than genksym software(crc32 not in armv8)
>> 3) zlib in arm64 recompile with +crc32 same speed with genksyms hardware
> 
> I think it would be useful to first have more data showing that the CRC
> calculation in genksyms is a hot path and contributes significantly to
> the overall kernel build time.
You are right.
1. genksyms contributes significantly to the overall kernel build time.
Test with arm64 defconfig and enable/disable CONFIG_GENKSYMS (11m50s/9m48s)
2. crc32 shows ~10% affect in perf record w/o patch.
3. but this patch w/o doesn`t affect the overall kernel build time 11m50s(+-1s).
4. so try to use zlib and delete the hard code crctab32 table?

BRs
Wentao Guan

RFC PATCH:
From f8f1c2301ddb70fb42a56fd7228db3dbd248e2b4 Mon Sep 17 00:00:00 2001
From: Wentao Guan <guanwentao@uniontech.com>
Date: Mon, 25 May 2026 20:02:03 +0800
Subject: [PATCH] genksyms: use crc32 from zlib

Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
---
 scripts/genksyms/Makefile   |  1 +
 scripts/genksyms/genksyms.c | 70 +++++--------------------------------
 2 files changed, 9 insertions(+), 62 deletions(-)

diff --git a/scripts/genksyms/Makefile b/scripts/genksyms/Makefile
index 4350311fb7b39..068e79626ffe7 100644
--- a/scripts/genksyms/Makefile
+++ b/scripts/genksyms/Makefile
@@ -7,6 +7,7 @@ genksyms-objs   := genksyms.o parse.tab.o lex.lex.o
 # -I needed for generated C source to include headers in source tree
 HOSTCFLAGS_parse.tab.o := -I $(src)
 HOSTCFLAGS_lex.lex.o := -I $(src)
+HOSTLDLIBS_genksyms :=  -lz
 
 # dependencies on generated files need to be listed explicitly
 $(obj)/lex.lex.o: $(obj)/parse.tab.h
diff --git a/scripts/genksyms/genksyms.c b/scripts/genksyms/genksyms.c
index 83e48670c2fcf..40d25dd898874 100644
--- a/scripts/genksyms/genksyms.c
+++ b/scripts/genksyms/genksyms.c
@@ -20,6 +20,7 @@
 #include <getopt.h>
 
 #include <hashtable.h>
+#include <zlib.h>
 
 #include "genksyms.h"
 /*----------------------------------------------------------------------*/
@@ -61,78 +62,23 @@ static void print_type_name(enum symbol_type type, const char *name);
 
 /*----------------------------------------------------------------------*/
 
-static const uint32_t crctab32[] = {
-       0x00000000U, 0x77073096U, 0xee0e612cU, 0x990951baU, 0x076dc419U,
-       0x706af48fU, 0xe963a535U, 0x9e6495a3U, 0x0edb8832U, 0x79dcb8a4U,
-       0xe0d5e91eU, 0x97d2d988U, 0x09b64c2bU, 0x7eb17cbdU, 0xe7b82d07U,
-       0x90bf1d91U, 0x1db71064U, 0x6ab020f2U, 0xf3b97148U, 0x84be41deU,
-       0x1adad47dU, 0x6ddde4ebU, 0xf4d4b551U, 0x83d385c7U, 0x136c9856U,
-       0x646ba8c0U, 0xfd62f97aU, 0x8a65c9ecU, 0x14015c4fU, 0x63066cd9U,
-       0xfa0f3d63U, 0x8d080df5U, 0x3b6e20c8U, 0x4c69105eU, 0xd56041e4U,
-       0xa2677172U, 0x3c03e4d1U, 0x4b04d447U, 0xd20d85fdU, 0xa50ab56bU,
-       0x35b5a8faU, 0x42b2986cU, 0xdbbbc9d6U, 0xacbcf940U, 0x32d86ce3U,
-       0x45df5c75U, 0xdcd60dcfU, 0xabd13d59U, 0x26d930acU, 0x51de003aU,
-       0xc8d75180U, 0xbfd06116U, 0x21b4f4b5U, 0x56b3c423U, 0xcfba9599U,
-       0xb8bda50fU, 0x2802b89eU, 0x5f058808U, 0xc60cd9b2U, 0xb10be924U,
-       0x2f6f7c87U, 0x58684c11U, 0xc1611dabU, 0xb6662d3dU, 0x76dc4190U,
-       0x01db7106U, 0x98d220bcU, 0xefd5102aU, 0x71b18589U, 0x06b6b51fU,
-       0x9fbfe4a5U, 0xe8b8d433U, 0x7807c9a2U, 0x0f00f934U, 0x9609a88eU,
-       0xe10e9818U, 0x7f6a0dbbU, 0x086d3d2dU, 0x91646c97U, 0xe6635c01U,
-       0x6b6b51f4U, 0x1c6c6162U, 0x856530d8U, 0xf262004eU, 0x6c0695edU,
-       0x1b01a57bU, 0x8208f4c1U, 0xf50fc457U, 0x65b0d9c6U, 0x12b7e950U,
-       0x8bbeb8eaU, 0xfcb9887cU, 0x62dd1ddfU, 0x15da2d49U, 0x8cd37cf3U,
-       0xfbd44c65U, 0x4db26158U, 0x3ab551ceU, 0xa3bc0074U, 0xd4bb30e2U,
-       0x4adfa541U, 0x3dd895d7U, 0xa4d1c46dU, 0xd3d6f4fbU, 0x4369e96aU,
-       0x346ed9fcU, 0xad678846U, 0xda60b8d0U, 0x44042d73U, 0x33031de5U,
-       0xaa0a4c5fU, 0xdd0d7cc9U, 0x5005713cU, 0x270241aaU, 0xbe0b1010U,
-       0xc90c2086U, 0x5768b525U, 0x206f85b3U, 0xb966d409U, 0xce61e49fU,
-       0x5edef90eU, 0x29d9c998U, 0xb0d09822U, 0xc7d7a8b4U, 0x59b33d17U,
-       0x2eb40d81U, 0xb7bd5c3bU, 0xc0ba6cadU, 0xedb88320U, 0x9abfb3b6U,
-       0x03b6e20cU, 0x74b1d29aU, 0xead54739U, 0x9dd277afU, 0x04db2615U,
-       0x73dc1683U, 0xe3630b12U, 0x94643b84U, 0x0d6d6a3eU, 0x7a6a5aa8U,
-       0xe40ecf0bU, 0x9309ff9dU, 0x0a00ae27U, 0x7d079eb1U, 0xf00f9344U,
-       0x8708a3d2U, 0x1e01f268U, 0x6906c2feU, 0xf762575dU, 0x806567cbU,
-       0x196c3671U, 0x6e6b06e7U, 0xfed41b76U, 0x89d32be0U, 0x10da7a5aU,
-       0x67dd4accU, 0xf9b9df6fU, 0x8ebeeff9U, 0x17b7be43U, 0x60b08ed5U,
-       0xd6d6a3e8U, 0xa1d1937eU, 0x38d8c2c4U, 0x4fdff252U, 0xd1bb67f1U,
-       0xa6bc5767U, 0x3fb506ddU, 0x48b2364bU, 0xd80d2bdaU, 0xaf0a1b4cU,
-       0x36034af6U, 0x41047a60U, 0xdf60efc3U, 0xa867df55U, 0x316e8eefU,
-       0x4669be79U, 0xcb61b38cU, 0xbc66831aU, 0x256fd2a0U, 0x5268e236U,
-       0xcc0c7795U, 0xbb0b4703U, 0x220216b9U, 0x5505262fU, 0xc5ba3bbeU,
-       0xb2bd0b28U, 0x2bb45a92U, 0x5cb36a04U, 0xc2d7ffa7U, 0xb5d0cf31U,
-       0x2cd99e8bU, 0x5bdeae1dU, 0x9b64c2b0U, 0xec63f226U, 0x756aa39cU,
-       0x026d930aU, 0x9c0906a9U, 0xeb0e363fU, 0x72076785U, 0x05005713U,
-       0x95bf4a82U, 0xe2b87a14U, 0x7bb12baeU, 0x0cb61b38U, 0x92d28e9bU,
-       0xe5d5be0dU, 0x7cdcefb7U, 0x0bdbdf21U, 0x86d3d2d4U, 0xf1d4e242U,
-       0x68ddb3f8U, 0x1fda836eU, 0x81be16cdU, 0xf6b9265bU, 0x6fb077e1U,
-       0x18b74777U, 0x88085ae6U, 0xff0f6a70U, 0x66063bcaU, 0x11010b5cU,
-       0x8f659effU, 0xf862ae69U, 0x616bffd3U, 0x166ccf45U, 0xa00ae278U,
-       0xd70dd2eeU, 0x4e048354U, 0x3903b3c2U, 0xa7672661U, 0xd06016f7U,
-       0x4969474dU, 0x3e6e77dbU, 0xaed16a4aU, 0xd9d65adcU, 0x40df0b66U,
-       0x37d83bf0U, 0xa9bcae53U, 0xdebb9ec5U, 0x47b2cf7fU, 0x30b5ffe9U,
-       0xbdbdf21cU, 0xcabac28aU, 0x53b39330U, 0x24b4a3a6U, 0xbad03605U,
-       0xcdd70693U, 0x54de5729U, 0x23d967bfU, 0xb3667a2eU, 0xc4614ab8U,
-       0x5d681b02U, 0x2a6f2b94U, 0xb40bbe37U, 0xc30c8ea1U, 0x5a05df1bU,
-       0x2d02ef8dU
-};
 
 static uint32_t partial_crc32_one(uint8_t c, uint32_t crc)
 {
-       return crctab32[(crc ^ c) & 0xff] ^ (crc >> 8);
+       return crc32(crc ^ 0xffffffff, (const unsigned char *)&c, 1) ^ 0xffffffff;
 }
 
 static uint32_t partial_crc32(const char *s, uint32_t crc)
 {
-       while (*s)
-               crc = partial_crc32_one(*s++, crc);
-       return crc;
+       return crc32(crc ^ 0xffffffff, (const unsigned char *)s, strlen(s)) ^ 0xffffffff;
 }
 
-static uint32_t crc32(const char *s)
+static uint32_t crc32_name(const char *s)
 {
-       return partial_crc32(s, 0xffffffff) ^ 0xffffffff;
+       return crc32(0, (const unsigned char *)s, strlen(s));
 }
 
+
 /*----------------------------------------------------------------------*/
 
 static enum symbol_type map_to_ns(enum symbol_type t)
@@ -154,7 +100,7 @@ struct symbol *find_symbol(const char *name, enum symbol_type ns, int exact)
 {
        struct symbol *sym;
 
-       hash_for_each_possible(symbol_hashtable, sym, hnode, crc32(name)) {
+       hash_for_each_possible(symbol_hashtable, sym, hnode, crc32_name(name)) {
                if (map_to_ns(sym->type) == map_to_ns(ns) &&
                    strcmp(name, sym->name) == 0 &&
                    sym->is_declared)
@@ -238,7 +184,7 @@ static struct symbol *__add_symbol(const char *name, enum symbol_type type,
                        return NULL;
        }
 
-       h = crc32(name);
+       h = crc32_name(name);
        hash_for_each_possible(symbol_hashtable, sym, hnode, h) {
                if (map_to_ns(sym->type) != map_to_ns(type) ||
                    strcmp(name, sym->name))
-- 
2.30.2