1. Fixing page offset check in funcslower

2. Not using BPF_F_REUSE_STACKID in funcslower stack traces
3. Combining an ifdef check

tools/funcslower.py

@@ -109,13 +109,9 @@ struct data_t {
 BPF_HASH(entryinfo, u64, struct entry_t);
 BPF_PERF_OUTPUT(events);
 
-#ifdef USER_STACKS
-BPF_STACK_TRACE(stacks, 2048);
-#else
-#ifdef KERNEL_STACKS
+#if defined(USER_STACKS) || defined(KERNEL_STACKS)
 BPF_STACK_TRACE(stacks, 2048);
 #endif
-#endif
 
 static int trace_entry(struct pt_regs *ctx, int id)
 {
@@ -167,21 +163,34 @@ int trace_return(struct pt_regs *ctx)
     data.retval = PT_REGS_RC(ctx);
 
 #ifdef USER_STACKS
-    data.user_stack_id = stacks.get_stackid(ctx, BPF_F_REUSE_STACKID | BPF_F_USER_STACK);
+    data.user_stack_id = stacks.get_stackid(ctx, BPF_F_USER_STACK);
 #endif
 
 #ifdef KERNEL_STACKS
-    data.kernel_stack_id = stacks.get_stackid(ctx, 0 | BPF_F_REUSE_STACKID);
+    data.kernel_stack_id = stacks.get_stackid(ctx, 0);
 
     if (data.kernel_stack_id >= 0) {
         u64 ip = PT_REGS_IP(ctx);
+        u64 page_offset;
 
         // if ip isn't sane, leave key ips as zero for later checking
-#ifdef CONFIG_RANDOMIZE_MEMORY
-        if (ip > __PAGE_OFFSET_BASE) {
+#if defined(CONFIG_X86_64) && defined(__PAGE_OFFSET_BASE)
+        // x64, 4.16, ..., 4.11, etc., but some earlier kernel didn't have it
+        page_offset = __PAGE_OFFSET_BASE;
+#elif defined(CONFIG_X86_64) && defined(__PAGE_OFFSET_BASE_L4)
+        // x64, 4.17, and later
+#if defined(CONFIG_DYNAMIC_MEMORY_LAYOUT) && defined(CONFIG_X86_5LEVEL)
+        page_offset = __PAGE_OFFSET_BASE_L5;
+#else
+        page_offset = __PAGE_OFFSET_BASE_L4;
+#endif
 #else
-        if (ip > PAGE_OFFSET) {
+        // earlier x86_64 kernels, e.g., 4.6, comes here
+        // arm64, s390, powerpc, x86_32
+        page_offset = PAGE_OFFSET;
 #endif
+
+        if (ip > page_offset) {
             data.kernel_ip = ip;
         }
     }