SYSV vs. Linux/GNU ELF formats

Question

The question is in the context of the following question: Why are libraries not found, even though they are clearly on the -L path? . It seems that my libraries and my object file have a different ELF format, which might cause the linker to not "find" the libraries.

Now, this leads to a couple of questions:

It seems that my compiler normally generates SYSV ELF files. (Checked with file). However, for that particular C++ source, it generates a Linux/GNU ELF object file. I wonder why, so I reduced that source to an empty main method - and suddenly I get a SYSV object file. What inside a C++ source file can cause the compiler to switch the ELF format?
Is it true or false that I can not link Linux/GNU together with SYSV ELF?
Is there an option to force the compiler to create a certain ELF format?

I'm working with a Cray g++ (GCC) 5.3.0 20151204.

@DustinOprea: Not really. The problem had a completely different cause. But since it finally worked without solving the SYSV issue, I conclude that it's probably possible to link the formats together. — Michael
– Michael, Commented Nov 12, 2017 at 9:33
I was going down this path as well, having a loader 'symbol lookup error' though the symbol is plainly in the right .so and the 'linkee' is showing the right file per ldd — Geof Sawaya
– Geof Sawaya, Commented Feb 8, 2018 at 7:27
6 yrs past no upvoted answer, somebody call some binutils guy to help. — Michaelzh
– Michaelzh, Commented Nov 29, 2023 at 9:09

Volker Simonis · Accepted Answer · 2018-09-24 09:52:33Z

0

Regarding question 1: one of the answer seems to be that functions of type STT_GNU_IFUNC will cause the compiler/linker to switch the ELF file format of the corresponding object file from SYSV to GNU/Linux.

However, I still couldn't find out how I can identify functions in an object file which have type STT_GNU_IFUNC. Looking at object files which are GNU/Linux with objdump, readelf and nm still don't show a single function of type STT_GNU_IFUNC.

Some more information on STT_GNU_IFUNC can be found at https://www.airs.com/blog/archives/403 and in the following related question: How do I compile on linux to share with all distributions?

answered Sep 24, 2018 at 9:52

Volker Simonis

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