[RFC PATCH v2] ld: Optionally nullify default PIE in all linker tests

[Hans-Peter Nilsson]

On Fri, 28 Mar 2025, Jens Remus wrote:

> Some distributions configure GCC with --enable-default-pie [1]. LLVM
> defaults Clang to CLANG_DEFAULT_PIE_ON_LINUX=ON [2].  This causes
> compiles to default to -fPIE and links to default to -pie, unless other
> options are explicitly given.  As a consequence several linker tests
> are compiled and linked in unexpected ways and may even unexpectedly
> fail or pass.
> 
> Add the configuration variable "NULLIFY_DEFAULT_PIE" to the linker test
> suite to optionally nullify default PIE, by prepending $NOPIE_CFLAGS to
> the compile flags and $NOPIE_LDFLAGS to the link flags for all linker
> tests.  These are then overridden by any deviating compiler flags
> (e.g. -fPIC or -fPIE) and linker flags (e.g -pie or -shared) explicitly
> specified by the tests.  Possible values of NULLIFY_DEFAULT_PIE are:
> 
>   0: Do not nullify default PIE. (default)
>   1: Unconditionally prefix $NOPIE_CLFAGS and $NOPIE_LDFLAGS.
>   auto: Prefix $NOPIE_CLFAGS and $NOPIE_LDFLAGS if compiler configured
>     to default to PIE.
> 
> NULLIFY_DEFAULT_PIE can for instance be specified via RUNTESTFLAGS:
> 
>   $ make check RUNTESTFLAGS="NULLIFY_DEFAULT_PIE=1"
> 
> or in ~/.dejagnurc:
> 
>   # Prefix $NOPIE_CLFAGS and $NOPIE_LDFLAGS if compiler defaults to PIE.
>   set nullify_default_pie "auto"

I can't help but thinking this is overthinking or 
overengineering, sorry.

Why not keep it simple: for each test creating an executable and 
that lacks an option mentioning specifying -pie -no-pie or 
-static, add "-no-pie"?  No $NOPIE_*.  (And subsequently make 
sure new tests mention such an option.)  IIRC, that's the way 
this (systems-having-different-pie-defaults) had been handled in 
the past.

For extra credit, for those tests with the new specified option, 
add an extra test with the inverted option, but as a separate 
patch.

brgds, H-P