[Bug ld/18801] PIE binary with STT_GNU_IFUNC symbol and TEXTREL segfaults on x86_64

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18801

--- Comment #12 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Sriraman Tallam from comment #10)
> 
> Isnt this similar to execstack in some sense?  I presume SELinux
> disallows that too but that we do not completely ban that on
> non-secure OS.

Since ld.so isn't changed, there is no run-time behavior change.

> I dont understand this as much as you do but I like Paul's idea here:
> 
> "I think it would be nice to have behavior other than what's currently
> happening. Either ld.so should support TEXTREL binaries with IFUNCs,
> or it should refuse to run them.

ld.so isn't responsible for user errors.

> I guess it could also try to make W+E page, and IF that fails, issue a
> warning and change to current behavior. That way, a TEXTREL+IFUNC
> binary will run correctly outside SELinux, will warn, then crash under
> SELinux. A TEXTREL without IFUNC will also run correctly outside
> SELinux, and will warn but still work under SELinux (i.e. almost same
> as current behavior)."

My ld patch issues an error:

./ld: read-only segment has dynamic IFUNC relocations; recompile with -fPIC or
link with -z execstack

Take your pick for workaround.

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