W + E load segments are not allowed

在進行android O的相容性驗證中，我們發現有應用force close，檢視log會有W + E load segments are not allowed。

08-10 15:37:30.616  3148  3148 W linker  : "/data/app/com.sxiaoao.fatpebble.clayjam.OPPO-Zwf5LGb1adpUq7SRfo8wvw==/lib/arm/libDexHelperUtil.so": W + E load segments are not allowed

08-10 15:37:30.629  3148  3148 W linker  : "/data/data/com.sxiaoao.fatpebble.clayjam.OPPO/.seccache/libDexHelper.so": W + E load segments are not allowed

08-10 15:37:30.646  3148  3148 F libc    : Fatal signal 11 (SIGSEGV), code 1, fault addr 0x0 in tid 3148 (le.clayjam.OPPO)

08-10 15:37:30.739  3175  3175 I crash_dump32: obtaining output fd from tombstoned

08-10 15:37:30.702  3175  3175 W crash_dump32: type=1400 audit(0.0:6583): avc: denied { search } for name="com.sxiaoao.fatpebble.clayjam.OPPO" dev="dm-0" ino=278577 scontext=u:r:crash_dump:s0:c512,c768 tcontext=u:object_r:app_data_file:s0:c512,c768 tclass=dir permissive=0

08-10 15:37:30.740  1290  1290 I /system/bin/tombstoned: received crash request for pid 3148

08-10 15:37:30.702  3175  3175 W crash_dump32: type=1400 audit(0.0:6584): avc: denied { search } for name="com.sxiaoao.fatpebble.clayjam.OPPO" dev="dm-0" ino=278577 scontext=u:r:crash_dump:s0:c512,c768 tcontext=u:object_r:app_data_file:s0:c512,c768 tclass=dir permissive=0

08-10 15:37:30.739  3175  3175 I crash_dump32: obtaining output fd from tombstoned

08-10 15:37:30.740  1290  1290 I /system/bin/tombstoned: received crash request for pid 3148

08-10 15:37:30.743  3175  3175 I crash_dump32: performing dump of process 3148 (target tid = 3148)

08-10 15:37:30.743  3175  3175 F DEBUG   : *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***

08-10 15:37:30.743  3175  3175 F DEBUG   : Build fingerprint: 'Android/msm8998/msm8998:8.0.0/OPR1.170623.011/lnxbui08040516:userdebug/test-keys'

08-10 15:37:30.743  3175  3175 F DEBUG   : Revision: '0'

08-10 15:37:30.743  3175  3175 F DEBUG   : ABI: 'arm'

08-10 15:37:30.743  3175  3175 F DEBUG   : pid: 3148, tid: 3148, name: le.clayjam.OPPO  >>> com.sxiaoao.fatpebble.clayjam.OPPO <<<

08-10 15:37:30.743  3175  3175 F DEBUG   : signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x0

08-10 15:37:30.743  3175  3175 F DEBUG   : Cause: null pointer dereference

08-10 15:37:30.743  3175  3175 F DEBUG   :     r0 00000006  r1 00004001  r2 00000000  r3 00000000

08-10 15:37:30.743  3175  3175 F DEBUG   :     r4 00000000  r5 0000287e  r6 edbfec50  r7 dbc7f800

08-10 15:37:30.743  3175  3175 F DEBUG   :     r8 ffc582a8  r9 00000099  sl eaa7615c  fp ead31230

08-10 15:37:30.744  3175  3175 F DEBUG   :     ip 00000000  sp ffc58180  lr cedb084f  pc cedb0850  cpsr 000d0030

08-10 15:37:30.744  3175  3175 F DEBUG   : 

08-10 15:37:30.744  3175  3175 F DEBUG   : backtrace:

08-10 15:37:30.744  3175  3175 F DEBUG   :     #00 pc 00027850  /data/data/com.sxiaoao.fatpebble.clayjam.OPPO/.seccache/libDexHelper.so (offset 0x8000)

08-10 15:37:30.744  3175  3175 F DEBUG   :     #01 pc 0002784d  /data/data/com.sxiaoao.fatpebble.clayjam.OPPO/.seccache/libDexHelper.so (offset 0x8000)

08-10 15:37:31.632  3175  3175 W crash_dump32: type=1400 audit(0.0:6589): avc: denied { search } for name="com.sxiaoao.fatpebble.clayjam.OPPO" dev="dm-0" ino=278577 scontext=u:r:crash_dump:s0:c512,c768 tcontext=u:object_r:app_data_file:s0:c512,c768 tclass=dir permissive=0

08-10 15:37:31.882  1290  1290 E /system/bin/tombstoned: Tombstone written to: /data/tombstones//tombstone_06

結合源碼其實很容易分析，

In the bionic/linker/linker_phdr.cpp,

 boolElfReader::LoadSegments() {

      int prot =PFLAGS_TO_PROT(phdr->p_flags);

      if ((prot& (PROT_EXEC | PROT_WRITE)) == (PROT_EXEC | PROT_WRITE)) {

        // W + EPT_LOAD segments are not allowed in O.

        if(get_application_target_sdk_version() >= __ANDROID_API_O__) {

         DL_ERR_AND_LOG("\"%s\": W + E load segments are not allowed",name_.c_str());

          return false;

        }

       DL_WARN("\"%s\": W + E load segments are notallowed", name_.c_str());

       add_dlwarning(name_.c_str(), "W+E load segments");

      }

So the flag in the so file segment should be not be W + E,or W + E PT_LOAD segments are not allowed in O

More details should refer the format information of so (ELFformat)