[WebAssembly] Allow absolute symbols in the linking section (symbol table) (#67493)

Fixes a crash in `-Wl,-emit-relocs` where the linker was not able to
write linker-synthetic absolute symbols to the symbol table.

This change adds a new symbol flag (`WASM_SYMBOL_ABS`), which means that
the symbol's offset is absolute and not relative to a given segment.
Such symbols include `__stack_low` and `__stack_low`.

Note that wasm object files never contains such symbols, only binaries
linked with `-Wl,-emit-relocs`.

Fixes: #67111

1 files changed, 13 insertions, 9 deletions

diff --git a/llvm/lib/Object/WasmObjectFile.cpp b/llvm/lib/Object/WasmObjectFile.cpp
index e9471ad..0982c7e 100644
--- a/llvm/lib/Object/WasmObjectFile.cpp
+++ b/llvm/lib/Object/WasmObjectFile.cpp
@@ -723,17 +723,21 @@ Error WasmObjectFile::parseLinkingSectionSymtab(ReadContext &Ctx) {
       Info.Name = readString(Ctx);
       if (IsDefined) {
         auto Index = readVaruint32(Ctx);
-        if (Index >= DataSegments.size())
-          return make_error<GenericBinaryError>("invalid data segment index",
-                                                object_error::parse_failed);
         auto Offset = readVaruint64(Ctx);
         auto Size = readVaruint64(Ctx);
-        size_t SegmentSize = DataSegments[Index].Data.Content.size();
-        if (Offset > SegmentSize)
-          return make_error<GenericBinaryError>(
-              "invalid data symbol offset: `" + Info.Name + "` (offset: " +
-                  Twine(Offset) + " segment size: " + Twine(SegmentSize) + ")",
-              object_error::parse_failed);
+        if (!(Info.Flags & wasm::WASM_SYMBOL_ABSOLUTE)) {
+          if (static_cast<size_t>(Index) >= DataSegments.size())
+            return make_error<GenericBinaryError>(
+                "invalid data segment index: " + Twine(Index),
+                object_error::parse_failed);
+          size_t SegmentSize = DataSegments[Index].Data.Content.size();
+          if (Offset > SegmentSize)
+            return make_error<GenericBinaryError>(
+                "invalid data symbol offset: `" + Info.Name +
+                    "` (offset: " + Twine(Offset) +
+                    " segment size: " + Twine(SegmentSize) + ")",
+                object_error::parse_failed);
+        }
         Info.DataRef = wasm::WasmDataReference{Index, Offset, Size};
       }
       break;