commit 6f1ceccf1443005248bec27bb24003124213a350
author Motomu Utsumi <motomuman@google.com> Wed Mar 19 19:49:08 2025 +0900
committer Motomu Utsumi <motomuman@google.com> Wed Mar 19 19:49:08 2025 +0900
tree fad099ae2a494e7daaf5744d82c7538203177e52
parent 0613620f404ce34afd39b12b53a962f3d71d2935

Skip enabling BTF on kernel older than 4.18

BPF_BTF_LOAD command was introduced in 4.18

Bug: 403381101
Test: boot on 4.9 kernel
Change-Id: Ibf2070750334417bd1052486c1f59a5d3f7fc20c

bpf/loader/NetBpfLoad.cpp

diff --git a/bpf/loader/NetBpfLoad.cpp b/bpf/loader/NetBpfLoad.cpp
index f11b9a3..d70a2c8 100644
--- a/bpf/loader/NetBpfLoad.cpp
+++ b/bpf/loader/NetBpfLoad.cpp
@@ -856,20 +856,24 @@
     ret = getSectionSymNames(elfFile, "maps", mapNames);
     if (ret) return ret;
 
-    ret = readSectionByName(".BTF", elfFile, btfData);
-    if (ret) {
-        ALOGE("Failed to read .BTF section, ret:%d", ret);
-        return ret;
-    }
-    struct btf *btf = btf__new(btfData.data(), btfData.size());
-    if (btf == NULL) {
-        ALOGE("btf__new failed, errno: %d", errno);
-        return -errno;
-    }
-    auto scopeGuard = base::make_scope_guard([btf] { btf__free(btf); });
+    struct btf *btf = NULL;
+    auto scopeGuard = base::make_scope_guard([btf] { if (btf) btf__free(btf); });
+    if (isAtLeastKernelVersion(4, 18, 0)) {
+        // On Linux Kernels older than 4.18 BPF_BTF_LOAD command doesn't exist.
+        ret = readSectionByName(".BTF", elfFile, btfData);
+        if (ret) {
+            ALOGE("Failed to read .BTF section, ret:%d", ret);
+            return ret;
+        }
+        struct btf *btf = btf__new(btfData.data(), btfData.size());
+        if (btf == NULL) {
+            ALOGE("btf__new failed, errno: %d", errno);
+            return -errno;
+        }
 
-    ret = loadBtf(elfFile, btf);
-    if (ret) return ret;
+        ret = loadBtf(elfFile, btf);
+        if (ret) return ret;
+    }
 
     unsigned kvers = kernelVersion();
 
@@ -997,7 +1001,7 @@
             if (isAtLeastKernelVersion(4, 15, 0))
                 strlcpy(req.map_name, mapNames[i].c_str(), sizeof(req.map_name));
 
-            bool haveBtf = isBtfSupported(type);
+            bool haveBtf = btf && isBtfSupported(type);
             if (haveBtf) {
                 uint32_t kTid, vTid;
                 ret = getKeyValueTids(btf, mapNames[i].c_str(), md[i].key_size,