tree 9f609fa8736a0f1346848642288a8b915ef94f23
parent 6fda5d4c5996775eb54c07116b9410145a4c1daa
author Fangrui Song <i@maskray.me> 1618600725 -0700
committer Copybara-Service <copybara-worker@google.com> 1618601124 -0700

[ELF] Default to -z start-stop-gc with a glibc "__libc_" special case

Change the default to facilitate GC for metadata section usage, so that they
don't need SHF_LINK_ORDER or SHF_GROUP just to drop the unhelpful rule (if they
want to be unconditionally retained, use SHF_GNU_RETAIN
(`__attribute__((retain))`) or linker script `KEEP`).

The dropped SHF_GROUP special case makes the behavior of -z start-stop-gc and -z
nostart-stop-gc closer to GNU ld>=2.37 (https://sourceware.org/PR27451).

However, we default to -z start-stop-gc (which actually matches more closely to
GNU ld before 2015-10 https://sourceware.org/PR19167), which is different from
modern GNU ld (which has the unhelpful rule to work around glibc). As a
compensation, we special case `__libc_` sections as a workaround for glibc<2.34
(https://sourceware.org/PR27492).

Since -z start-stop-gc as the default actually matches the traditional GNU ld
behavior, there isn't much to be aware of. There was a systemd usage which has
been fixed by https://github.com/systemd/systemd/pull/19144

GitOrigin-RevId: 6d2d3bd0a61f5fc7fd9f61f48bc30e9ca77cc619