[fpc-pascal] Reproducible code: DLL calling Firebird crashes
Mark Morgan Lloyd
markMLl.fpc-pascal at telemetry.co.uk
Tue Sep 30 11:27:10 CEST 2014
Reinier Olislagers wrote:
> On 29/09/2014 19:30, Reinier Olislagers wrote:
>> Re bug report: agreed. I'll raise it.
Jonas has already closed it, noting
The entry-point function should perform only simple initialization or
termination tasks. It must not call the LoadLibrary or LoadLibraryEx
function (or a function that calls these functions), because this may
create dependency loops in the DLL load order. This can result in a DLL
being used before the system has executed its initialization code.
"I.e., what you are doing is unsupported ("must not call the LoadLibrary
or LoadLibraryEx function"). I think that on most unix platforms, trying
to load libraries from other the init function of other libraries is not
However I'd precede that by a thought based on what Jose said. In your
example, you're opening the database in the initialisation block of
businesslayer.pas, which is invoked at an arbitrary position in the init
sequence of the DLL/so. If that operation were moved instead to the
initialisation block of testdbdll.lpr, which in the context of the
DLL/so is analogous to a program's main block, it might work.
If having the open operation in testdbdll.lpr works but having it in
businesslayer.pas doesn't, then it's fair to ask why in the context of
FPC (hence my suggestion of a bug report). If neither works, then it's
presumably explained by Jonas's note i.e. it's a "feature" in the
context of the library loader.
In practice, I still think it's best for the main program to tell the
database when and how to initialise, since there's things that it might
know about the user's intentions or environment that aren't known by the
dynamically-loaded libraries (crude example: you might want to know the
compile-time name of the project of which the main program was a part).
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
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