[RISCV] Make mapping symbols SF_FormatSpecific

[jobnoorman]

Summary

This ensures that llvm-symbolizer ignores them for symbolization.

Note: unlike aarch64-mapping-symbol.s, the test included here does not
test if the mapping symbols are actually in the symbol table. The reason
is that llvm-mc support for RISC-V mapping symbols (D153260) has not
landed yet, so the mapping symbols simply aren't there. However, D153260
would like to depend on this patch together with D156190 to avoid having
to update a large amount of tests.

[MaskRay]

llvm/test/DebugInfo/Symbolize/ELF/riscv-mapping-symbol.s

5

llvm-nm verification for other architectures is useful.

[MaskRay]

Due to how the llvm-nm code is currently constructed, consider adding tools/llvm-nm/special-syms-riscv.test as well.

[jhenderson]

llvm/test/DebugInfo/Symbolize/ELF/riscv-mapping-symbol.s

3

[jobnoorman]

Fix typo

[jobnoorman]

In D156236#4541112, @MaskRay wrote:

Due to how the llvm-nm code is currently constructed, consider adding tools/llvm-nm/special-syms-riscv.test as well.

I've opened D156514 for this as some changes to llvm-nm were needed.

llvm/test/DebugInfo/Symbolize/ELF/riscv-mapping-symbol.s

5

I'm not entirely sure what you mean by this. Are you talking about the special-syms test for llvm-nm?

llvm/include/llvm/Object/ELFObjectFile.h

if (Expected<StringRef> NameOrErr = getSymbolName(Sym)) {
       if (Name.startswith("$d") || Name.startswith("$t"))
         Result |= SymbolRef::SF_FormatSpecific;
     } else {
       // TODO: Actually report errors helpfully.
       consumeError(NameOrErr.takeError());
     }
   } else if (EF.getHeader().e_machine == ELF::EM_RISCV) {
     if (Expected<StringRef> NameOrErr = getSymbolName(Sym)) {
-      // Mark empty name symbols used for label differences.
-      if (NameOrErr->empty())
+      StringRef Name = *NameOrErr;
+      // Mark empty name symbols (used for label differences) and mapping
+      // symbols.
+      if (Name.empty() || Name.startswith("$d") || Name.startswith("$x"))
         Result |= SymbolRef::SF_FormatSpecific;
     } else {
       // TODO: Actually report errors helpfully.
       consumeError(NameOrErr.takeError());
     }
   }
 
   if (ESym->st_shndx == ELF::SHN_UNDEF)

llvm/test/DebugInfo/Symbolize/ELF/riscv-mapping-symbol.s

+# REQUIRES: riscv-registered-target
+## Ignore RISC-V mapping symbols (with a prefix of $d or $x).
+
+# RUN: llvm-mc -filetype=obj -triple=riscv64 %s -o %t
+# RUN: llvm-symbolizer --obj=%t 0 4 0xc | FileCheck %s
+
+# CHECK:      foo
+# CHECK-NEXT: ??:0:0
+# CHECK-EMPTY:
+# CHECK:      foo
+# CHECK-NEXT: ??:0:0
+# CHECK-EMPTY:
+# CHECK:      foo
+# CHECK-NEXT: ??:0:0
+
+    .global foo
+foo:
+    .word 32
+    nop
+    nop
+    .word 42