Emit all constant integers produced by SanitizerBinaryMetadata as
ULEB128 to further reduce binary space used. Increasing the version is
not necessary given this change depends on (and will land) along with
the bump to v2.
To support this, the !pcsections metadata format is extended to allow
for per-section options, encoded in the first MD operator which must
always be a string and contain the section: "<section>!<options>".
Reviewed By: dvyukov
Differential Revision: https://reviews.llvm.org/D143484
Optimize the encoding of "covered" metadata by:
1. Reducing feature mask from 4 bytes to 1 byte (needs increase once we
reach more than 8 features).
2. Only emitting UAR stack args size if it is non-zero, saving 4 bytes
in the common case.
One caveat is that the emitted metadata for function PC (offset), size,
and UAR size (if enabled) are no longer aligned to 4 bytes.
SanitizerBinaryMetadata version base is increased to 2, since the change
is backwards incompatible.
Reviewed By: dvyukov
Differential Revision: https://reviews.llvm.org/D143482
D130887 uses a dummy empty section `sanmd_covered` (with the SHF_GNU_RETAIN flag on
ELF) to prevent `undefined symbol: __start_sanmd_covered` if all `sanmd_covered`
are discarded by `ld --gc-sections` (in `-z start-stop-gc` mode).
The dummy `sanmd_covered` does not have the SHF_LINK_ORDER flag, so mixing it
with SHF_LINK_ORDER `sanmd_covered` causes an issue to GNU ld<2.36
(https://sourceware.org/bugzilla/show_bug.cgi?id=26256).
Similar to D98903 for SanitizerCoverage, let's make encapsulation symbols
undefined weak[1]. This additionally avoids size cost due to the dummy section and
symbol.
[1]: https://maskray.me/blog/2021-01-31-metadata-sections-comdat-and-shf-link-order
Reviewed By: melver
Differential Revision: https://reviews.llvm.org/D139276
Introduces the frontend flag -fexperimental-sanitize-metadata=, which
enables SanitizerBinaryMetadata instrumentation.
The first intended user of the binary metadata emitted will be a variant
of GWP-TSan [1]. The plan is to open source a stable and production
quality version of GWP-TSan. The development of which, however, requires
upstream compiler support.
[1] https://llvm.org/devmtg/2020-09/slides/Morehouse-GWP-Tsan.pdf
Until the tool has been open sourced, we mark this kind of
instrumentation as "experimental", and reserve the option to change
binary format, remove features, and similar.
Reviewed By: vitalybuka, MaskRay
Differential Revision: https://reviews.llvm.org/D130888
