[all-commits] [llvm/llvm-project] 4286f4: [AArch64][GCS][LLD] Introduce -zgcs-report-dynamic...

[Jack Styles via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 4286f4dccee9140eef3ef7d059619eaab73fc392
      https://github.com/llvm/llvm-project/commit/4286f4dccee9140eef3ef7d059619eaab73fc392
  Author: Jack Styles <jack.styles at arm.com>
  Date:   2025-03-15 (Sat, 15 Mar 2025)

  Changed paths:
    M lld/ELF/Config.h
    M lld/ELF/Driver.cpp
    M lld/ELF/InputFiles.cpp
    M lld/ELF/InputFiles.h
    M lld/docs/ReleaseNotes.rst
    M lld/test/ELF/aarch64-feature-gcs.s

  Log Message:
  -----------
  [AArch64][GCS][LLD] Introduce -zgcs-report-dynamic Command Line Option (#127787)

When GCS was introduced to LLD, the gcs-report option allowed for a user
to gain information relating to if their relocatable objects supported
the feature. For an executable or shared-library to support GCS, all
relocatable objects must declare that they support GCS.

The gcs-report checks were only done on relocatable object files,
however for a program to enable GCS, the executable and all shared
libraries that it loads must enable GCS. gcs-report-dynamic enables
checks to be performed on all shared objects loaded by LLD, and in cases
where GCS is not supported, a warning or error will be emitted.

It should be noted that only shared files directly passed to LLD are
checked for GCS support. Files that are noted in the `DT_NEEDED` tags
are assumed to have had their GCS support checked when they were
created.

The behaviour of the -zgcs-dynamic-report option matches that of GNU ld.
The behaviour is as follows unless the user explicitly sets the value:
* -zgcs-report=warning or -zgcs-report=error implies
-zgcs-report-dynamic=warning.

This approach avoids inheriting an error level if the user wishes to
continue building a module without rebuilding all the shared libraries.
The same approach was taken for the GNU ld linker, so behaviour is
identical across the toolchains.

This implementation matches the error message and command line interface
used within the GNU ld Linker. See here:

https://github.com/bminor/binutils-gdb/commit/724a8341f6491283cf90038260c83a454b7268ef

To support this option being introduced, two other changes are included
as part of this PR. The first converts the -zgcs-report option to
utilise an Enum, opposed to StringRef values. This enables easier
tracking of the value the user defines when inheriting the value for the
gas-report-dynamic option. The second is to parse the Dynamic Objects
program headers to locate the GNU Attribute flag that shows GCS is
supported. This is needed so, when using the gcs-report-dynamic option,
LLD can correctly determine if a dynamic object supports GCS.

---------

Co-authored-by: Fangrui Song <i at maskray.me>



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