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
