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

[Yasumasa Suenaga]

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
>