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

[Chris Plummer]

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
>>>
>