Thread: Conflicting function name in dynamically-loaded shared library
Hi: I am wanting to define some functions as described in section 35.9 of the manual, "C-Language Functions." I am compiling pre-existing files of c-code from another project into object files, and then linking those object files into a shared library along with my own functions that follow the posgresql calling convention, invoking other functions as desired. This pre-existing c-code I'm compiling happens to contain a function named "point_add()". I see the postgresql source file fmgrtab.c also has a function with the same name. When my code tries to invoke its version of point_add() I get a bus error, and when I changed the name of that function to something else the bus error went away. Of course, since I'm working with source code I can just keep the modified function name, but I would like to be able to keep my version of this c code updated with that project and so to use it unmodified. So my questions are: first, might I be wrong about the cause of this bus error? I cannot think of another reason why changing the name of a function would have this effect, but maybe there's some other reason besides the "point_add()" function in fmgrtab.c conflicting. If so, I'm interested to know. If, however, it is probable that this bus error is a result of this naming conflict, then do I have any options for working around it that would enable me to use the code from this other library without changing the name of its "point_add()" function? I know I could ask that project's developers to change the function's name, but that could break other code that currently uses it, and even if it didn't, I would prefer something less intrusive on that project. Thanks very much for any ideas about this, -- Adam Mackler
Adam Mackler wrote: > I am wanting to define some functions as described in section 35.9 of > the manual, "C-Language Functions." I am compiling pre-existing files > of c-code from another project into object files, and then linking > those object files into a shared library along with my own functions > that follow the posgresql calling convention, invoking other functions > as desired. > > This pre-existing c-code I'm compiling happens to contain a function > named "point_add()". I see the postgresql source file fmgrtab.c also > has a function with the same name. When my code tries to invoke its > version of point_add() I get a bus error, and when I changed the name > of that function to something else the bus error went away. > > Of course, since I'm working with source code I can just keep the > modified function name, but I would like to be able to keep my version > of this c code updated with that project and so to use it unmodified. > > So my questions are: first, might I be wrong about the cause of this > bus error? I cannot think of another reason why changing the name of > a function would have this effect, but maybe there's some other reason > besides the "point_add()" function in fmgrtab.c conflicting. If so, > I'm interested to know. > > If, however, it is probable that this bus error is a result of this > naming conflict, then do I have any options for working around it that > would enable me to use the code from this other library without > changing the name of its "point_add()" function? I know I could ask > that project's developers to change the function's name, but that > could break other code that currently uses it, and even if it didn't, > I would prefer something less intrusive on that project. If you are on Linux, you could try the following patch: http://www.postgresql.org/message-id/CA+CSw_tPDYgnzCYW0S4oU0mTUoUhZ9pc7MRBPXVD-3Zbiwni9w@mail.gmail.com Maybe that will make it work, then you know that your suspicion was correct. But what you describe should definitely cause a problem, though "bus error" sounds surprising to me. Renaming one of the functions seems like the best thing to do. It would need a convincing case (like, many people have that problem) to get the name changed in PostgreSQL. Yours, Laurenz Albe
On Wed, Jan 28, 2015 at 11:23:15AM +0000, Albe Laurenz wrote: > If you are on Linux, you could try the following patch: > > http://www.postgresql.org/message-id/CA+CSw_tPDYgnzCYW0S4oU0mTUoUhZ9pc7MRBPXVD-3Zbiwni9w@mail.gmail.com > > ... > Renaming one of the functions seems like the best thing to do. I am using FreeBSD, so RTLD_DEEPBIND is not supported by my dlopen(). However, your suggestion to rename the function seems at least as good. Patching PostgreSQL would just mean trading difficulties when upgrading the third-party library for difficulties when upgrading PostgreSQL. Thank you for the response and insight. -- Adam Mackler