[LLD] Add CLASS syntax to SECTIONS (#95323)

This allows the input section matching algorithm to be separated from
output section descriptions. This allows a group of sections to be
assigned to multiple output sections, providing an explicit version of
--enable-non-contiguous-regions's spilling that doesn't require altering
global linker script matching behavior with a flag. It also makes the
linker script language more expressive even if spilling is not intended,
since input section matching can be done in a different order than
sections are placed in an output section.

The implementation reuses the backend mechanism provided by
--enable-non-contiguous-regions, so it has roughly similar semantics and
limitations. In particular, sections cannot be spilled into or out of
INSERT, OVERWRITE_SECTIONS, or /DISCARD/. The former two aren't
intrinsic, so it may be possible to relax those restrictions later.

1 files changed, 2 insertions, 0 deletions

diff --git a/lld/ELF/MapFile.cpp b/lld/ELF/MapFile.cpp
index c4f3fdd..1bad529 100644
--- a/lld/ELF/MapFile.cpp
+++ b/lld/ELF/MapFile.cpp
@@ -167,6 +167,8 @@ static void writeMapFile(raw_fd_ostream &os) {
       os << assign->commandString << '\n';
       continue;
     }
+    if (isa<SectionClassDesc>(cmd))
+      continue;
 
     osec = &cast<OutputDesc>(cmd)->osec;
     writeHeader(os, osec->addr, osec->getLMA(), osec->size, osec->addralign);