[fpc-devel] Fix for an annoying error

J. Gareth Moreton gareth at moreton-family.com
Tue Nov 30 17:49:42 CET 2021


Well, running the program on the target system isn't a guaranteed 
success even if there's no error on the compilation system because the 
DLL in question may be different (or missing).

If it turns out that common.dll is not required, then the maintainer of 
the package should probably remove the $linklib line, otherwise I'm not 
sure.  If I'm right in thinking, if the DLL is missing or incompatible, 
it won't read the exports table and so even if just a warning is raised, 
it may cause a cascade error if any of its functions are used in the 
unit because they're not declared.

Gareth aka. Kit

On 30/11/2021 16:22, Michael Van Canneyt via fpc-devel wrote:
>
>
> On Tue, 30 Nov 2021, J. Gareth Moreton via fpc-devel wrote:
>
>> That was a conundrum I was trying to answer when making the patch.  
>> What is a warning and what is an error?
>>
>> A lot of the verification code is dependent on compile-time constants 
>> whose values depend on the compiler's target platform, including 
>> header sizes, so any mismatch is an error case, and the checking of 
>> header sizes and the COFF magic number are done together, since the 
>> correct header size is dependent on the magic number's value.
>>
>> I didn't look too much further beyond the verification code, but if 
>> it's able to detect if a DLL is 32-bit on a 64-bit system and vice 
>> versa, I feel that's a warning rather than error because, in my 
>> experience, it's down to a default system configuration (I got the 
>> error on a freshly-installed machine) rather than something 
>> untoward.  If the DLL is missing, that should probably be a warning 
>> too and I'll see if I can make that change.  A corrupted DLL is 
>> definitely an error though.
>>
>> I didn't do a verification to see if the DLL is for AArch64, for 
>> example, since that situation is more unlikely.  It also starts to 
>> bloat the compiler code.
>>
>> Either way, using a DLL for a different build of Windows is a warning 
>> at the very least because the project will probably break when you 
>> try to run it.
>
> Personally, I think that reverting to a warning was a mistake.
>
> You have no guarantee that the resulting program will run if you 
> ignore the
> "error":
>
> Not on the system where you compiled, not on the system where you will 
> run the program.
>
> For your particular problem: I looked at the source code of the oracle 
> unit.
> As far as I can see there is no need to include the common.dll in the
> linklib statements, all that should be linked is the oracle dll. It 
> may be a better solution simply to remove that line.
>
> Michael.
>
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