The C compiler on some platforms (such as s390x) assumes that the
data pointed to by symbols meets certain alignment requirements.
The swift sections do not necessarily meet these alignment
requirements so this change adds alignment attributes to them to
force the compiler to emit the instruction sequences and relocations
required to address unaligned data.
This fixes a 'R_390_PC32DBL target misaligned' warning issued by
gold on s390x.
Search through the new section containing Swift protocol descriptor
references to resolve protocols by mangled name. Use this
functionality to support protocol composition types within
_typeForMangledName.
The separate section of type references uses the same type reference format
as in protocol conformance records. As with protocol conformance records,
mangle the type reference kind into the lower two bits. Then, eliminate the
separate "flags" field from the type metadata record. Finally, rename
the section because the Swift 5 stable format for this section is
different from prior formats, and the two runtimes need to be able to
coexist.
The format of protocol conformance records will be changing in Swift 5, so
rename the segment (from, e.g., __swift2_proto to __swift5_proto) to allow
Swift < 5 and Swift 5+ runtimes to coexist.
Restructure the ELF handling to be completely agnostic to the OS.
Rather than usng the loader to query the section information, use the
linker to construct linker tables and synthetic markers for the
beginning and of the table. Save off the values of these pointers and
pass them along through the constructor to the runtime for registration.
This removes the need for the begin/end objects. Remove the special
construction of the begin/end objects through the special assembly
constructs, preferring to do this in C with a bit of inline assembly to
ensure that the section is always allocated.
Remove the special handling for the various targets, the empty object
file can be linked on all the targets.
The new object file has no requirements on the ordering. It needs to
simply be injected into the link.
Name the replacement file `swiftrt.o` mirroring `crt.o` from libc. Merge
the constructor and the definition into a single object file.
This approach is generally more portable, overall simpler to implement,
and more robust.
Thanks to Orlando Bassotto for help analyzing some of the odd behaviours
when switching over.
