【android9.0】system/core下的usbhost模块无法输出log到logcat

现象：原生android9.0 sdk，system/core/libusbhost是usb模块用来和驱动通信的模块，在调试时希望能输出log到logcat，打开调试开关重新编译代码，报“undefined reference to '__android_log_print'”错误

FAILED: out/soong/.intermediates/system/core/libusbhost/libusbhost/linux_glibc_x86_64_shared/libusbhost.so 
prebuilts/clang/host/linux-x86/clang-4691093/bin/clang++  @out/soong/.intermediates/system/core/libusbhost/libusbhost/linux_glibc_x86_64_shared/libusbhost.so.rsp out/soong/.intermediates/external/compiler-rt/libcompiler_rt-extras/linux_glibc_x86_64_static/libcompiler_rt-extras.a out/soong/.intermediates/external/libcxx/libc++/linux_glibc_x86_64_shared/libc++.so  -o out/soong/.intermediates/system/core/libusbhost/libusbhost/linux_glibc_x86_64_shared/libusbhost.so -shared -Wl,-soname,libusbhost.so -target x86_64-linux-gnu -Bprebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/x86_64-linux/bin  -Wl,--no-undefined -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now -Wl,--no-undefined-version --gcc-toolchain=prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8 --sysroot prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot -m64 -Bprebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/lib/gcc/x86_64-linux/4.8 -Lprebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/lib/gcc/x86_64-linux/4.8 -Lprebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/x86_64-linux/lib64 -ldl -lpthread -lm -lrt -Wl,-rpath,\$ORIGIN/../lib64 -Wl,-rpath,\$ORIGIN/lib64  -nodefaultlibs -lgcc_s -lgcc -lc -lgcc_s -lgcc
system/core/libusbhost/usbhost.c:211: error: undefined reference to '__android_log_print'
system/core/libusbhost/usbhost.c:278: error: undefined reference to '__android_log_print'
system/core/libusbhost/usbhost.c:301: error: undefined reference to '__android_log_print'
system/core/libusbhost/usbhost.c:305: error: undefined reference to '__android_log_print'
clang-6.0: error: linker command failed with exit code 1 (use -v to see invocation)
[ 16% 97/605] Construct recovery from boot
ninja: build stopped: subcommand failed.
11:04:39 ninja failed with: exit status 1

问题原因：

此问题的根本原因是，编译系统在链接时找不到相应的函数实现体，与头文件缺失无关，即函数实现体所在的liblog库无法被找到

解决办法：修改Android.bp，将liblog共享库声明放在target外面，暂不清楚放target里边为什么会链接不到

diff --git a/libusbhost/Android.bp b/libusbhost/Android.bp
old mode 100644
new mode 100755
index fc6f305..43076eb
--- a/libusbhost/Android.bp
+++ b/libusbhost/Android.bp
@@ -24,13 +24,16 @@ cc_library {
     srcs: ["usbhost.c"],
     cflags: ["-Werror"],
     export_include_dirs: ["include"],
+    shared_libs: [
+       "liblog",
+    ],
     target: {
         android: {
             cflags: [
                 "-g",
                 "-DUSE_LIBLOG",
             ],
-            shared_libs: ["liblog"],
+            //shared_libs: ["liblog"],
         },
         darwin: {
             enabled: false,