rdar://186556339
Resolves https://github.com/swiftlang/swift/issues/91943
setTrueConstGlobal pins metadata into .rodata on ELF, but LLVM still derives
the section flags from the initializer. Two cases produced a writable
.rodata ("aw"), which GNU ld folds into the text segment, yielding an RWX
LOAD segment on AArch64 Linux (where it defaults to -z noseparate-code):
- Mangled-name references are tagged by setting the low bit with a
non-inbounds GEP. Constant::getRelocationInfo only recognizes a relative
reference as a link-time constant if it can strip the operands' offsets
with stripInBoundsConstantOffsets, so these were classified as needing a
dynamic relocation. This hit every conformance descriptor with an
associated/base conformance entry (Hashable, Comparable, the synthesized
CodingKeys: CodingKey, ...). Use inbounds GEPs instead. +1 into a string of
at least two bytes is in bounds.
- Key path patterns were created as non-constant globals. The pattern is
never written at runtime (the once cache is the separate keypath_once
global, and on Darwin the pattern already lives in __TEXT,__const), so
mark it constant.
Also assert in setTrueConstGlobal that the global is constant.
Adds a cross-target test checking that the object file has no writable
.rodata, and an AArch64 Linux executable test checking that linking with
the default linker produces no RWX segment.
Dario Rexin
f6268ecd88