format_datum debugging function
Hi Hackers,
Often in a debugger I've wanted to way to print Datums, in particular non-trivial ones like range
types. This came up a lot when I was working on multiranges, and I've wished for it lately while
working on UPDATE/DELETE FOR PORTION OF. But all the obvious approaches are inlined functions or
preprocessor macros, so they aren't available. Usually I wind up giving up on gdb and adding elog
statements. Once or twice I've copy/pasted from the three or four levels of nested macros to make
gdb do what I wanted, but it's a pain.
I assumed printing a Datum was easy, and I was the only one who didn't know how to do it. But
perhaps not. The conversation about print.c [1]/messages/by-id/7d023c20-6679-44bd-b5f7-44106659bd5a@eisentraut.org made me think I should propose a way to make it
easier. This function takes a Datum and the appropriate out function, and returns a char *. So you
can do this:
(gdb) call format_datum(range_out, $1)
$2 = 0x59162692d938 "[1,4)"
I assume a patch like this doesn't need documentation. Does it need a test? Anything else?
[1]: /messages/by-id/7d023c20-6679-44bd-b5f7-44106659bd5a@eisentraut.org
Yours,
--
Paul ~{:-)
pj@illuminatedcomputing.com
Hi Paul,
[...] This function takes a Datum and the appropriate out function, and returns a char *. So you
can do this:(gdb) call format_datum(range_out, $1)
$2 = 0x59162692d938 "[1,4)"I assume a patch like this doesn't need documentation. Does it need a test? Anything else?
I think you forgot to attach the patch. Or is it just a proposal?
--
Best regards,
Aleksander Alekseev
On 8/12/24 04:32, Aleksander Alekseev wrote:
[...] This function takes a Datum and the appropriate out function, and returns a char *. So you
can do this:(gdb) call format_datum(range_out, $1)
$2 = 0x59162692d938 "[1,4)"I assume a patch like this doesn't need documentation. Does it need a test? Anything else?
I think you forgot to attach the patch. Or is it just a proposal?
Sorry, patch attached here.
Yours,
--
Paul ~{:-)
pj@illuminatedcomputing.com
Attachments:
v1-0001-Add-format_datum-debugging-function.patchtext/x-patch; charset=UTF-8; name=v1-0001-Add-format_datum-debugging-function.patchDownload+20-1
On Mon, 12 Aug 2024 at 23:15, Paul Jungwirth
<pj@illuminatedcomputing.com> wrote:
On 8/12/24 04:32, Aleksander Alekseev wrote:
(gdb) call format_datum(range_out, $1)
$2 = 0x59162692d938 "[1,4)"I assume a patch like this doesn't need documentation. Does it need a test? Anything else?
I think you forgot to attach the patch. Or is it just a proposal?
Sorry, patch attached here.
+1 for the idea. And the code looks trivial enough. I think this
should also contain a print_datum function too though.
On 12.08.24 23:15, Paul Jungwirth wrote:
On 8/12/24 04:32, Aleksander Alekseev wrote:
[...] This function takes a Datum and the appropriate out function,
and returns a char *. So you
can do this:(gdb) call format_datum(range_out, $1)
$2 = 0x59162692d938 "[1,4)"I assume a patch like this doesn't need documentation. Does it need a
test? Anything else?I think you forgot to attach the patch. Or is it just a proposal?
Sorry, patch attached here.
I don't think it's safe to call output functions at arbitrary points
from a debugger. But if you're okay with that during development, say,
then I think you could just call OidOutputFunctionCall(F_RANGE_OUT, $1)?
On 8/14/24 02:16, Peter Eisentraut wrote:
On 12.08.24 23:15, Paul Jungwirth wrote:
On 8/12/24 04:32, Aleksander Alekseev wrote:
[...] This function takes a Datum and the appropriate out function, and returns a char *. So you
can do this:(gdb) call format_datum(range_out, $1)
$2 = 0x59162692d938 "[1,4)"I assume a patch like this doesn't need documentation. Does it need a test? Anything else?
I think you forgot to attach the patch. Or is it just a proposal?
Sorry, patch attached here.
I don't think it's safe to call output functions at arbitrary points from a debugger. But if you're
okay with that during development, say, then I think you could just call
OidOutputFunctionCall(F_RANGE_OUT, $1)?
I assumed it wasn't safe everywhere (e.g. there is potentially a TOAST lookup), but for debugging a
patch that's okay with me.
Are you doing something to get macro expansion? I've never gotten my gdb to see #defines, although
in theory this configure line should do it, right?:
./configure 'CFLAGS=-ggdb -Og -g3 -fno-omit-frame-pointer' --enable-tap-tests --enable-cassert
--enable-debug --prefix=${HOME}/local
I also tried -gdwarf and -gdwarf-4 and -gdwarf-5 (all still with -Og -g3).
If it makes a difference, I'm attaching to a process:
paul@tal:~/src/postgresql$ gdb -p 1175735
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Attaching to process 1175735
Reading symbols from /home/paul/local/bin/postgres...
Reading symbols from /lib/x86_64-linux-gnu/libz.so.1...
(No debugging symbols found in /lib/x86_64-linux-gnu/libz.so.1)
Reading symbols from /lib/x86_64-linux-gnu/libm.so.6...
Reading symbols from /usr/lib/debug/.build-id/a5/08ec5d8bf12fb7fd08204e0f87518e5cd0b102.debug...
Reading symbols from /lib/x86_64-linux-gnu/libicui18n.so.70...
(No debugging symbols found in /lib/x86_64-linux-gnu/libicui18n.so.70)
Reading symbols from /lib/x86_64-linux-gnu/libicuuc.so.70...
(No debugging symbols found in /lib/x86_64-linux-gnu/libicuuc.so.70)
Reading symbols from /lib/x86_64-linux-gnu/libc.so.6...
Reading symbols from /usr/lib/debug/.build-id/49/0fef8403240c91833978d494d39e537409b92e.debug...
Reading symbols from /lib64/ld-linux-x86-64.so.2...
Reading symbols from /usr/lib/debug/.build-id/41/86944c50f8a32b47d74931e3f512b811813b64.debug...
Reading symbols from /lib/x86_64-linux-gnu/libstdc++.so.6...
(No debugging symbols found in /lib/x86_64-linux-gnu/libstdc++.so.6)
Reading symbols from /lib/x86_64-linux-gnu/libgcc_s.so.1...
(No debugging symbols found in /lib/x86_64-linux-gnu/libgcc_s.so.1)
Reading symbols from /lib/x86_64-linux-gnu/libicudata.so.70...
(No debugging symbols found in /lib/x86_64-linux-gnu/libicudata.so.70)
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
0x000079878e325dea in epoll_wait (epfd=7, events=0x573f0e475820, maxevents=1, timeout=-1) at
../sysdeps/unix/sysv/linux/epoll_wait.c:30
30 ../sysdeps/unix/sysv/linux/epoll_wait.c: No such file or directory.
(gdb) b range_in
Breakpoint 1 at 0x573f0d9b5042: file rangetypes.c, line 91.
(gdb) c
Continuing.
Breakpoint 1, range_in (fcinfo=0x7fff6d8fea90) at rangetypes.c:91
91 {
(gdb) fin
Run till exit from #0 range_in (fcinfo=0x7fff6d8fea90) at rangetypes.c:91
0x0000573f0da8c87e in InputFunctionCall (flinfo=0x7fff6d8feb20, str=0x573f0e47a258 "[3,5)",
typioparam=3904, typmod=-1) at fmgr.c:1547
1547 result = FunctionCallInvoke(fcinfo);
Value returned is $1 = 95928334988456
(gdb) call OidOutputFunctionCall(F_RANGE_OUT, $1)
No symbol "F_RANGE_OUT" in current context.
If I know the oid, then this works:
(gdb) call OidOutputFunctionCall(3835, $1)
$2 = 0x5f9be16ca4d8 "[3,5)"
That is a big improvement, but still a little annoying.
Thanks,
--
Paul ~{:-)
pj@illuminatedcomputing.com
On 14.08.24 17:46, Paul Jungwirth wrote:
On 8/14/24 02:16, Peter Eisentraut wrote:
On 12.08.24 23:15, Paul Jungwirth wrote:
On 8/12/24 04:32, Aleksander Alekseev wrote:
[...] This function takes a Datum and the appropriate out function,
and returns a char *. So you
can do this:(gdb) call format_datum(range_out, $1)
$2 = 0x59162692d938 "[1,4)"I assume a patch like this doesn't need documentation. Does it need
a test? Anything else?I think you forgot to attach the patch. Or is it just a proposal?
Sorry, patch attached here.
I don't think it's safe to call output functions at arbitrary points
from a debugger. But if you're okay with that during development,
say, then I think you could just call
OidOutputFunctionCall(F_RANGE_OUT, $1)?I assumed it wasn't safe everywhere (e.g. there is potentially a TOAST
lookup), but for debugging a patch that's okay with me.Are you doing something to get macro expansion? I've never gotten my gdb
to see #defines, although in theory this configure line should do it,
right?:
Oh I see, you don't have the F_* constants available then. Maybe just
put in the OID manually then?
Peter Eisentraut <peter@eisentraut.org> writes:
On 14.08.24 17:46, Paul Jungwirth wrote:
Are you doing something to get macro expansion? I've never gotten my gdb
to see #defines, although in theory this configure line should do it,
right?:
Oh I see, you don't have the F_* constants available then. Maybe just
put in the OID manually then?
That's pretty illegible and error-prone. I agree that writing the
output function's C name is noticeably better. However, I would
call the result DirectOutputFunctionCall and put it near
OidOutputFunctionCall in fmgr.c. It's not like we don't already
have a naming convention and many instances of this.
(Also, now that I look at the code, I wonder why it looks so
little like any of the existing DirectFunctionCall functions.)
regards, tom lane