Help Resolving Compiler Errors With enable-dtrace Flag
Hey folks,
I'm working on a custom version of Postgres that is roughly in line with
16.4 but has customizations in it. I'm trying to compile this custom
version (on Linux) with `--enable-dtrace` but I'm running into an issue
during the linker stage. I've done a clean and full rebuild but that
doesn't help fix the problem. I get these errors for all probes:
access/transam/xact.o(.note.stapsdt+0x24): error: undefined reference
to 'postgresql_transaction__start_semaphore'
access/transam/xact.o(.note.stapsdt+0x78): error: undefined reference
to 'postgresql_transaction__commit_semaphore'
access/transam/xact.o(.note.stapsdt+0xcc): error: undefined reference
to 'postgresql_transaction__abort_semaphore'
I can see the probes.h file gets generated what looks to be correctly,
specifically these:
__extension__ extern unsigned short
postgresql_transaction__commit_semaphore __attribute__ ((unused))
__attribute__ ((section (".probes")));
I have compiled vanilla pg16.4 with the same flags and the probes got
created and linked as expected with no issues so I'm assuming there is some
difference in the custom version that is causing the errors but I'm having
a hard time tracking it down. I'm wondering if anyone here has any
experience with this error or has any hints as to why the linker can't find
these definitions or even just where the actual definitions for these
probes should live so I can try to work backwards and see if there is any
differences in the custom version that is messing with the linker.
Thanks!
Re: Help Resolving Compiler Errors With enable-dtrace Flag
> Now you tell us? > > If that's the case, I wonder whether probes.o is getting built > correctly and included in the link. The relevant bits are in > src/backend/Makefile ... they don't look that easy to mess up, > but maybe. I thought I mentioned it in my original message but it wasn't super clear. I just checked and you're right, the probes.o is not getting built for some reason. I don't even see it attempting to in the build output and when I add a debug print statement to the utils/probes.o rule I don't see that in the output. Either way that most certainly explains why I'm getting that error and gives me something to dig in to more. Thanks for the help!
Re: Help Resolving Compiler Errors With enable-dtrace Flag
>I'd read > > https://www.postgresql.org/docs/current/dynamic-trace.html#DEFINING-TRACE-POINTS > > >and then go see if those tracepoints are fully conforming to the >coding rules in the modified version. A plausible bet is that >their entries in probes.d don't entirely match up with the calls >in the source code. You could compare the relevant bits of code >between vanilla and modified 16.4 if the problem isn't immediately >obvious. > >regards, tom lane I've taken a look at the probes.d file and there are no changes between the modified and vanilla versions of the file, and the probes are called with the same args. This is happening for every probe in the probes.d file. Since I'm getting those errors it looks like the generated probes.h file is also properly being used. Do you know where the postgresql_transaction__commit_semaphore symbol should be defined?
Re: Help Resolving Compiler Errors With enable-dtrace Flag
> Was the customization done under version control? Yes it was. My thinking though is that I am getting this error with every probe, not just the ones in xact.c so I suspect there is something more than just a code change to the file. I compared the common makefiles and don't see any changes that would cause the linker error. In any case I'll try to go back through some of the commit history to see if anything stands out. Thanks for the input!
Re: Help Resolving Compiler Errors With enable-dtrace Flag
Unfortunately the people remaining are just as lost as me. No one has attempted to build with dtrace so I'm in uncharted territory. A diff of the object file doesn't give any useful information, the custom version has a lot of differences since there have been a number of changes from stock. postgresql_transaction__commit_semaphore does exist in the symbol table of both .o files though when compared with objdump. On Sun, Oct 20, 2024 at 1:50 PM Adrian Klaver wrote: > On 10/20/24 09:30, Barry Walker wrote: > > Hey folks, > > > I have compiled vanilla pg16.4 with the same flags and the probes got > > created and linked as expected with no issues so I'm assuming there is > > some difference in the custom version that is causing the errors but I'm > > having a hard time tracking it down. I'm wondering if anyone here has > > any experience with this error or has any hints as to why the linker > > can't find these definitions or even just where the actual definitions > > for these probes should live so I can try to work backwards and see if > > there is any differences in the custom version that is messing with > > the linker. > > Talking to the folks that created the custom version is not possible? > > If you do a diff on: > > access/transam/xact.o > > between the stock and custom version does it shed any light? > > > > > Thanks! > > -- > Adrian Klaver > adrian.kla...@aklaver.com > >
