preload-pass.test fails with glibc

[miller-alex]

preload-pass.test fails with glibc

[0-wiz-0]

Do you know a symbol we could use instead?
Does 'remove@@' work?

[miller-alex]

No, remove@@ doesn't help. The symbol versions have to match exactly, or the symbol from the preloaded library will not be considered.

In this case it gets a little complicated because different libcs (in case of glibc even different (sub)archs) use different symbol versions (or none). So I guess you have to check what version gets actually used:

• Link nihtest-file before libineffective-remove.so.
• List its dynamic symbols, e.g. with nm -D nihtest-file.
• Find the symbol you want to override (i.e. remove) and extract the symbol version, if any.
• If the symbol has a version suffix, then link libineffective-remove.so with a version script that sets the expected symbol version.

Alternatively, you could search for the default version of remove in libc, i.e. the one with @@ in the name (there is no other version in my libc, though). That is slightly more complicated (you have to find the correct libc) but could be done in the configure step.

The version script should look like @REMOVE_VER@ { global: remove; }; where @REMOVE_VER@ is to be replaced by the expected symbol version. For example, on my system, where nihtest-file has an undefind symbol remove@GLIBC_2.2.5,
the version script becomes GLIBC_2.2.5 { global: remove; };.
Pass the version script to the linker with -Wl,--version-script=libineffective-remove.map assuming the version script file name is libineffective-remove.map.

I don't know whether cmake provides support that can simplify the task.

See https://sourceware.org/binutils/docs/ld/VERSION.html for basic info on symbol versions and linker scripts or https://www.akkadia.org/drepper/dsohowto.pdf for more background.

[0-wiz-0]

I took a different route - in the test we're not really interested in if we can override a libc symbol, it's enough if we can override a symbol from a library. So I made a library and overrode its symbol.
Please verify that this fixes the problem for you too!

[miller-alex]

With 266c455 applied, tests work as expected here:

100% tests passed, 0 tests failed out of 54

Total Test time (real) =   4.01 sec

The following tests did not run:
         44 - preload-skip.test (Skipped)

Thanks for the quick fix.