commit 311f8b325e31cfcb54e30678b54c60d303cfec39
author Patrick Rohr <prohr@google.com> Mon May 15 19:58:49 2023 -0700
committer Patrick Rohr <prohr@google.com> Wed May 17 15:39:38 2023 -0700
tree b7da8675ace7fb2ce82787e09617c1da21c759fc
parent 432291a3344db891dc776994995dd16c95582b62

BpfRingbuf: support 32 bit userspace

Both consumer and producer position are wrapped in an std::atomic and
extended to uint64_t to enforce atomic access.

See resulting assembly instructions for aosp_cf_x86_phone-userdebug:

frameworks/libs/net/common/native/bpf_headers/include/bpf/BpfRingbuf.h:212
  2d:   8b 41 18                mov    0x18(%ecx),%eax
external/libcxx/include/atomic:926 (discriminator 4)
  30:   f3 0f 7e 00             movq   (%eax),%xmm0

This will not work on a 32 bit kernel (so we might want to explicitly
check for that in the test).

Test: atest BpfRingbufTest
Change-Id: I7fec435cbe49d392363d05f7e702d82ecacb9e91

staticlibs/native/bpf_headers/BpfRingbufTest.cpp

diff --git a/staticlibs/native/bpf_headers/BpfRingbufTest.cpp b/staticlibs/native/bpf_headers/BpfRingbufTest.cpp
index d23afae..f348333 100644
--- a/staticlibs/native/bpf_headers/BpfRingbufTest.cpp
+++ b/staticlibs/native/bpf_headers/BpfRingbufTest.cpp
@@ -25,6 +25,7 @@
 #include "BpfSyscallWrappers.h"
 #include "bpf/BpfRingbuf.h"
 #include "bpf/BpfUtils.h"
+#include "bpf/KernelUtils.h"
 
 #define TEST_RINGBUF_MAGIC_NUM 12345
 
@@ -49,8 +50,8 @@
       GTEST_SKIP() << "BPF ring buffers not supported below 5.8";
     }
 
-    if (sizeof(unsigned long) != 8) {
-      GTEST_SKIP() << "BPF ring buffers not supported on 32 bit arch";
+    if (!isKernel64Bit()) {
+      GTEST_SKIP() << "BPF ring buffers not supported on 32 bit kernel";
     }
 
     errno = 0;