Re: [PATCH bpf-next v4] selftests/bpf: trace_helpers.c: optimize kallsyms cache

On 8/16/23 3:36 AM, Rong Tao wrote:

From: Rong Tao rongtao@cestc.cn

Static ksyms often have problems because the number of symbols exceeds the MAX_SYMS limit. Like changing the MAX_SYMS from 300000 to 400000 in commit e76a014334a6("selftests/bpf: Bump and validate MAX_SYMS") solves the problem somewhat, but it's not the perfect way.

This commit uses dynamic memory allocation, which completely solves the problem caused by the limitation of the number of kallsyms.

Acked-by: Stanislav Fomichev sdf@google.com Signed-off-by: Rong Tao rongtao@cestc.cn

---

v4: Make sure most cases we don't need the realloc() path to begin with, and check strdup() return value. v3: https://lore.kernel.org/lkml/tencent_50B4B2622FE7546A5FF9464310650C008509@qq... Do not use structs and judge ksyms__add_symbol function return value. v2: https://lore.kernel.org/lkml/tencent_B655EE5E5D463110D70CD2846AB3262EED09@qq... Do the usual len/capacity scheme here to amortize the cost of realloc, and don't free symbols. v1: https://lore.kernel.org/lkml/tencent_AB461510B10CD484E0B2F62E3754165F2909@qq...

---

tools/testing/selftests/bpf/trace_helpers.c | 46 ++++++++++++++++----- 1 file changed, 36 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c index f83d9f65c65b..a1461508925e 100644 --- a/tools/testing/selftests/bpf/trace_helpers.c +++ b/tools/testing/selftests/bpf/trace_helpers.c @@ -18,10 +18,35 @@ #define TRACEFS_PIPE "/sys/kernel/tracing/trace_pipe" #define DEBUGFS_PIPE "/sys/kernel/debug/tracing/trace_pipe" -#define MAX_SYMS 400000 -static struct ksym syms[MAX_SYMS]; +static struct ksym *syms; +static int sym_cap; static int sym_cnt; +static int ksyms__add_symbol(const char *name, unsigned long addr) +{

• void *tmp;
• unsigned int new_cap;
• if (sym_cnt + 1 > sym_cap) {

• new_cap = sym_cap * 4 / 3;
  

• tmp = realloc(syms, sizeof(struct ksym) * new_cap);
  

• if (!tmp)
  

• 	return -ENOMEM;
  

• syms = tmp;
  

• sym_cap = new_cap;
  

• }
• tmp = strdup(name);
• if (!tmp)

• return -ENOMEM;
  

• syms[sym_cnt].addr = addr;
• syms[sym_cnt].name = tmp;
• sym_cnt++;
• return 0;

+}

Since this patch is about improving the load_kallsyms_refresh(), I mentioned in the v3 that it would also be good to have the counterpart to release the allocated memory once the test concluded or upon error given it's dynamically allocated.

static int ksym_cmp(const void *p1, const void *p2) { return ((struct ksym *)p1)->addr - ((struct ksym *)p2)->addr; @@ -33,9 +58,14 @@ int load_kallsyms_refresh(void) char func[256], buf[256]; char symbol; void *addr;

• int i = 0;

• int ret;

• /* Make sure most cases we don't need the realloc() path to begin with */
• sym_cap = 400000; sym_cnt = 0;
• syms = malloc(sizeof(struct ksym) * sym_cap);
• if (!syms)

• return -ENOMEM;
  

f = fopen("/proc/kallsyms", "r"); if (!f) @@ -46,15 +76,11 @@ int load_kallsyms_refresh(void) break; if (!addr) continue;

• if (i >= MAX_SYMS)
  

• 	return -EFBIG;
  

• syms[i].addr = (long) addr;
  

• syms[i].name = strdup(func);
  

• i++;
  

• ret = ksyms__add_symbol(func, (unsigned long)addr);
  

• if (ret)
  

• 	return ret;
  

  } fclose(f);

• sym_cnt = i; qsort(syms, sym_cnt, sizeof(struct ksym), ksym_cmp); return 0; }

Thanks, Daniel