[lldb-dev] Various strange errors while debugging PostgreSQL
Hello
Here is what I do. In one terminal I connect to PostgreSQL using psql
command. In another terminal I determine pid of a new PostgreSQL
process (backend process that handles a new connection) and run:
```
lldb-3.7.1 -p (pid)
```
Then:
```
b heap_open
c
```
In first terminal:
```
create temporary table tt1(x int);
```
In second terminal:
```
1290 {
1291 Relationr;
1292
-> 1293 r = relation_open(relationId, lockmode);
1294
1295 if (r->rd_rel->relkind == RELKIND_INDEX)
1296 ereport(ERROR,
(lldb) p r
(Relation) $0 = 0x0002018a70c8
(lldb) p r->rd_rel
error: Couldn't apply expression side effects : Couldn't dematerialize
a result variable: couldn't read its memory
```
This is a first issue. The second issue is:
```
(lldb) process save-core /tmp/1.core
error: Failed to save core file for process: no ObjectFile plugins were
able to save a core for this process
```
LLDB was compiled manually from RELEASE_371/final tag using clang 3.6:
```
cmake ../llvm -G Ninja -DLLDB_DISABLE_CURSES:BOOL=TRUE \
-DCMAKE_C_COMPILER=/usr/bin/clang-3.6 \
-DCMAKE_CXX_COMPILER=/usr/bin/clang++-3.6 \
-DCMAKE_BUILD_TYPE=Release
ninja -j2
sudo ninja install
```
It's Ubuntu Linux 14.04 LTS:
```
$ uname -a
Linux pgsql-dev-ubuntu 3.13.0-83-generic #127-Ubuntu SMP Fri Mar 11
00:25:37 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
```
Same issues with lldb-3.6 installed using apt-get.
`process save-core` doesn't work in lldb-3.8 compiled using ports on
FreeBSD 10.2 as well. Unfortunately I can't tell if first bug reproduces
on FreeBSD because of another bug I reported previously:
https://llvm.org/bugs/show_bug.cgi?id=26924#c3
Anyway are these some sort of well-know issues that could be bypassed
somehow or brand new bugs? I can also provide any other debug
information you might need.
--
Best regards,
Aleksander Alekseev
http://eax.me/
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Re: [lldb-dev] Various strange errors while debugging PostgreSQL
> (lldb) p r->rd_rel > error: Couldn't apply expression side effects : Couldn't dematerialize >a result variable: couldn't read its memory OK, this issue is fixed in 3.8.0. Two others are not. -- Best regards, Aleksander Alekseev http://eax.me/ ___ lldb-dev mailing list lldb-dev@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
Re: [lldb-dev] Various strange errors while debugging PostgreSQL
> So I am guessing these are the only architectures that are supported.
> I am guessing you might be on an i386 system?
No I'm afraid it's x86_64. File RegisterContextPOSIXCore_x86_64.cpp is
present in source tree I used to build lldb.
This bug is very easy to reproduce.
0. You need Ubuntu 14.04 LTS x64 with latest updates
1. Create a new LXC container to exclude any possible side effects from
other installed applications
2. Build LLDB using this script: http://paste.ubuntu.com/15488691/
3. Run `sudo ninja install`
4. Create t.c:
```
#include
int main()
{
printf("Hello!\n");
return 0;
}
```
5. Run ` /usr/local/bin/clang-3.8 t.c -o t ` (or ... -g - it doesn't
matter)
6. Then:
$ ./t
Hello!
$ lldb ./t
(lldb) target create "./t"
Current executable set to './t' (x86_64).
(lldb) b main
Breakpoint 1: where = t`main, address = 0x00400530
(lldb) r
Process 24974 launching
Process 24974 launched: './t' (x86_64)
Process 24974 stopped
* thread #1: tid = 24974, 0x00400530 t`main, name = 't', stop
reason = breakpoint 1.1 frame #0: 0x00400530 t`main
-> 0x400530 : pushq %rbp
0x400531 : movq %rsp, %rbp
0x400534 : subq $0x10, %rsp
0x400538 : movabsq $0x4005e4, %rdi
(lldb) process save-core /tmp/1.core
error: Failed to save core file for process: no ObjectFile plugins were
able to save a core for this process
(lldb) ^D
--
Best regards,
Aleksander Alekseev
http://eax.me/
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