`--shuffle-sections=<seed>` applies to all sections. The new
`--shuffle-sections=<section-glob>=<seed>` makes shuffling selective. To the
best of my knowledge, the option is only used as debugging, so just drop the
original form.
`--shuffle-sections '.init_array*=-1'` `--shuffle-sections '.fini_array*=-1'`.
reverses static constructors/destructors of the same priority.
Useful to detect some static initialization order fiasco.
`--shuffle-sections '.data*=-1'`
reverses `.data*` sections. Useful to detect unfunded pointer comparison results
of two unrelated objects.
If certain sections have an intrinsic order, the old form cannot be used.
Differential Revision: https://reviews.llvm.org/D98679
If the number of sections changes, which is common for re-links after
incremental updates, the section order may change drastically.
Special case -1 to reverse input sections. This is a stable transform.
The section order is more resilient to incremental updates. Usually the
code issue (e.g. Static Initialization Order Fiasco, assuming pointer
comparison result of two unrelated objects) is due to the relative order
between two problematic input files A and B. Checking the regular order
and the reversed order is sufficient.
Differential Revision: https://reviews.llvm.org/D98445
With this --shuffle-sections=seed produces the same result in every
host.
Reviewed By: grimar, MaskRay
Differential Revision: https://reviews.llvm.org/D74971
Summary:
This option causes lld to shuffle sections by assigning different
priorities in each run.
The use case for this is to introduce randomization in benchmarks. The
idea is inspired by the paper "Producing Wrong Data Without Doing
Anything Obviously Wrong!"
(https://www.inf.usi.ch/faculty/hauswirth/publications/asplos09.pdf). Unlike
the paper, we shuffle individual sections, not just input files.
Doing this in lld is particularly convenient as the --reproduce option
makes it easy to collect all the necessary bits for relinking the
program being benchmarked. Once that it is done, all that is needed is
to add --shuffle-sections=0 to the response file and relink before each
run of the benchmark.
Differential Revision: https://reviews.llvm.org/D74791
Fangrui Song