RFR(XS): 8248878: SA: Implement simple workaround for JDK-8248876

[Chris Plummer]

Hello,

Can I get a second reviewer please. Yasumasa has done the first review. 
The discussion below was all about how to possibly fix JDK-8248876, but 
for now we're sticking with this workaround.

http://cr.openjdk.java.net/~cjplummer/8248878/webrev.00/index.html
https://bugs.openjdk.java.net/browse/JDK-8248878

The explanation of the fix is in the CR. The parent CR, JDK-8248876 [1], 
explains the issue being addressed.

There's no test for this fix yet. It requires the changes I'm making for 
JDK-8247514 [2], which include changes to "findpc" support and the 
ClhsdbFindPC.java test that trigger this issue.

[1] https://bugs.openjdk.java.net/browse/JDK-8248876
[2] https://bugs.openjdk.java.net/browse/JDK-8247514

thanks,

Chris

On 7/13/20 4:48 PM, Yasumasa Suenaga wrote:
> Sure, I reviewed for this workaround (JDK-8248878).
>
> I'm still think we can use note section in the core for JDK-8248876 as 
> I said, but I'm not sure.
>
>
> Thanks,
>
> Yasumasa
>
>
> On 2020/07/14 3:12, Chris Plummer wrote:
>> Hi Yasumasa,
>>
>> If you have no further suggestions on how to fix JDK-8248876, I'd 
>> like to proceed with this work around. Can I considered it reviewed 
>> by you?
>>
>> thanks,
>>
>> Chris
>>
>> On 7/7/20 7:29 PM, Chris Plummer wrote:
>>> Hi Yasumasa,
>>>
>>> The executable is not opened with pathmap_open:
>>>
>>>   if ((ph->core->exec_fd = open(exec_file, O_RDONLY)) < 0) {
>>>
>>> I think pathmap_open() is just used for libraries.
>>>
>>> thanks,
>>>
>>> Chris
>>>
>>> On 7/7/20 6:18 PM, Yasumasa Suenaga wrote:
>>>> Hi Chris,
>>>>
>>>> SA would use `link_map` to decide to load address, but it does not 
>>>> seem to contain executable.
>>>> I set breakpoint to pathmap_open() and I watched the argument of 
>>>> it, then I didn't see any executable (`java`) on it.
>>>> Maybe current implementation is broken.
>>>>
>>>> I guess we can use note section in the core for deciding loading 
>>>> address.
>>>> I can see valid address (includes executable) from `readelf -n`.
>>>> Of course it might be big change for SA...
>>>>
>>>>
>>>> Thanks,
>>>>
>>>> Yasumasa
>>>>
>>>>
>>>> On 2020/07/07 15:38, Chris Plummer wrote:
>>>>> Hi Yasumasa,
>>>>>
>>>>> Thanks for the review. I tried the following for line 188:
>>>>>
>>>>>      if ((phdr->p_type == PT_LOAD || phdr->p_type == PT_INTERP) && 
>>>>> phdr->p_vaddr < baseaddr) {
>>>>>
>>>>> However, "base" still ended up being 0. I added some printfs. For 
>>>>> the exec file there is both a PT_INTER with p_vaddr of 0x238 and a 
>>>>> PT_LOAD with p_vaddr 0. I'm not sure which to use, but in either 
>>>>> case that won't be the proper base when added to 0:
>>>>>
>>>>>    if (add_lib_info_fd(ph, exec_file, ph->core->exec_fd,
>>>>>                        (uintptr_t)0 + 
>>>>> find_base_address(ph->core->exec_fd, &exec_ehdr)) == NULL) {
>>>>>      goto err;
>>>>>    }
>>>>>
>>>>> So maybe it's the (uintptr_t)0 that is the problem here. For 
>>>>> shared libs instead of 0 it computes the value to add:
>>>>>
>>>>>                 if (lib_base_diff == ZERO_LOAD_ADDRESS ) {
>>>>>                   lib_base_diff = calc_prelinked_load_address(ph, 
>>>>> lib_fd, &elf_ehdr, link_map_addr);
>>>>>                   if (lib_base_diff == INVALID_LOAD_ADDRESS) {
>>>>>                     close(lib_fd);
>>>>>                     return false;
>>>>>                   }
>>>>>                 }
>>>>>
>>>>>                 lib_base = lib_base_diff + 
>>>>> find_base_address(lib_fd, &elf_ehdr);
>>>>>
>>>>> So in this case we've actually computed lib_base_diff rather than 
>>>>> just assumed 0.
>>>>>
>>>>> Chris
>>>>>
>>>>> On 7/6/20 10:46 PM, Yasumasa Suenaga wrote:
>>>>>> Hi Chris,
>>>>>>
>>>>>> Your change looks good.
>>>>>>
>>>>>>
>>>>>> BTW I saw JDK-8248876. I'm not sure, but I guess we can fix this 
>>>>>> issue if we allow PT_INTERP in L118:
>>>>>>
>>>>>> ```
>>>>>> 105 uintptr_t find_base_address(int fd, ELF_EHDR* ehdr) {
>>>>>>                   :
>>>>>> 115   // the base address of a shared object is the lowest vaddr of
>>>>>> 116   // its loadable segments (PT_LOAD)
>>>>>> 117   for (phdr = phbuf, cnt = 0; cnt < ehdr->e_phnum; cnt++, 
>>>>>> phdr++) {
>>>>>> 118     if (phdr->p_type == PT_LOAD && phdr->p_vaddr < baseaddr) {
>>>>>> 119       baseaddr = phdr->p_vaddr;
>>>>>> 120     }
>>>>>> 121   }
>>>>>> ```
>>>>>>
>>>>>> /proc/<PID>/maps shows top of `java` is 0x56543b9df000:
>>>>>>
>>>>>> 56543b9df000-56543b9e0000 r--p 00000000 08:10 55770 
>>>>>> /usr/lib/jvm/java-11-openjdk-amd64/bin/java
>>>>>>
>>>>>>
>>>>>> `i target` on GDB shows 0x56543b9df000 is .interp section:
>>>>>>
>>>>>> Local exec file:
>>>>>>         `/usr/lib/jvm/java-11-openjdk-amd64/bin/java', file type 
>>>>>> elf64-x86-64.
>>>>>>         Entry point: 0x56543b9e0330
>>>>>>         0x000056543b9df318 - 0x000056543b9df334 is .interp
>>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>> Yasumasa
>>>>>>
>>>>>>
>>>>>> On 2020/07/07 13:18, Chris Plummer wrote:
>>>>>>> Hello,
>>>>>>>
>>>>>>> Please help review the following:
>>>>>>>
>>>>>>> http://cr.openjdk.java.net/~cjplummer/8248878/webrev.00/index.html
>>>>>>> https://bugs.openjdk.java.net/browse/JDK-8248878
>>>>>>>
>>>>>>> The explanation of the fix is in the CR. The parent CR, 
>>>>>>> JDK-8248876 [1], explains the issue being addressed.
>>>>>>>
>>>>>>> There's no test for this fix yet. It requires the changes I'm 
>>>>>>> making for JDK-8247514 [2], which include changes to "findpc" 
>>>>>>> support and the ClhsdbFindPC.java test that trigger this issue.
>>>>>>>
>>>>>>> [1] https://bugs.openjdk.java.net/browse/JDK-8248876
>>>>>>> [2] https://bugs.openjdk.java.net/browse/JDK-8247514
>>>>>>>
>>>>>>> thanks,
>>>>>>>
>>>>>>> Chris
>>>>>
>>>
>>
>>