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

[Chris Plummer]

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