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Re: Question about the ldd output

On 2019-07-05 12:28, Lavrentiev, Anton (NIH/NLM/NCBI) [C] via cygwin wrote:
> Here's the output from ldd, of an executable built just recently on Cygwin:
>         ntdll.dll => /cygdrive/c/WINDOWS/SYSTEM32/ntdll.dll (0x7ffc339d0000)
>         KERNEL32.DLL => /cygdrive/c/WINDOWS/System32/KERNEL32.DLL (0x7ffc31a00000)
>         KERNELBASE.dll => /cygdrive/c/WINDOWS/System32/KERNELBASE.dll (0x7ffc30090000)
>         cygwin1.dll => /cygdrive/u/2.4.0/release/Cygwin-64/bin/cygwin1.dll (0x180040000)
>         cygiconv-2.dll => /usr/bin/cygiconv-2.dll (0x3ec980000)
>         cygcom_err-2.dll => /usr/bin/cygcom_err-2.dll (0x3ef750000)
>         cygbz2-1.dll => /usr/bin/cygbz2-1.dll (0x3f6a40000)
>         cyggcc_s-seh-1.dll => /usr/bin/cyggcc_s-seh-1.dll (0x3ee3a0000)
>         cyggssapi_krb5-2.dll => /usr/bin/cyggssapi_krb5-2.dll (0x3eceb0000)
>         cygz.dll => /cygdrive/u/2.4.0/release/Cygwin-64/bin/cygz.dll (0x3aba30000)
>         cygpcre-1.dll => /usr/bin/cygpcre-1.dll (0x3eb1a0000)
>         cygk5crypto-3.dll => /usr/bin/cygk5crypto-3.dll (0x3ec300000)
>         cygintl-8.dll => /usr/bin/cygintl-8.dll (0x3ec8d0000)
>         cygkrb5support-0.dll => /usr/bin/cygkrb5support-0.dll (0x3ec150000)
>         ??? => ??? (0x90000)
> My question would be, how to read the last line? It'd be quite suspicious if 
> ldd is unable to figure out what library (name) is required (the left side
> of the =>), but I understand that the library itself might be missing (so
> it's logical to put "???" on the right side in that case).
> Any insight is appreciated.

I found many Cygwin exes that display zero to multiple lines like that,
depending on the run, but it was flakey and inconsistent, and could not find any
common factors across builds.
Across 1684 /bin/exes, about 400 exes displayed about 600 lines with '???'.

That looks like it might be a limitation of how ldd works under Cygwin.
If you compare ldd output to cygcheck output from the same exe, ldd always omits
and cygcheck always includes the following on my W10 Home:


so what we are seeing may be an artifact of Windows dll load table entries, as
Windows programs can not be built with unresolved dll links, but Cygwin
dynamically autoloads dlls when functions are called.

Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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