[ELF] Produce DT_RISCV_VARIANT_CC

riscv-non-isa/riscv-elf-psabi-doc#190 introduced STO_RISCV_VARIANT_CC.
The linker should:

* Copy the STO_RISCV_VARIANT_CC bit to .symtab/.dynsym: already fulfilled after
  82ed93e
* Produce DT_RISCV_VARIANT_CC if at least one R_RISCV_JUMP_SLOT relocation
  references a symbol with the STO_RISCV_VARIANT_CC bit. Done by this patch.

Reviewed By: kito-cheng

Differential Revision: https://reviews.llvm.org/D107951

lld/ELF/SyntheticSections.cpp

@@ -1420,6 +1420,14 @@ DynamicSection<ELFT>::computeContents() {
                   r.sym->stOther & STO_AARCH64_VARIANT_PCS;
           }) != in.relaPlt->relocs.end())
         addInt(DT_AARCH64_VARIANT_PCS, 0);
+      addInSec(DT_PLTGOT, *in.gotPlt);
+      break;
+    case EM_RISCV:
+      if (llvm::any_of(in.relaPlt->relocs, [](const DynamicReloc &r) {
+            return r.type == target->pltRel &&
+                   (r.sym->stOther & STO_RISCV_VARIANT_CC);
+          }))
+        addInt(DT_RISCV_VARIANT_CC, 0);
       [[fallthrough]];
     default:
       addInSec(DT_PLTGOT, *in.gotPlt);

lld/docs/ReleaseNotes.rst

@@ -33,6 +33,9 @@ ELF Improvements
   (`D133548 <https://reviews.llvm.org/D133548>`_)
 * ``--no-warnings``/``-w`` is now available to suppress warnings.
   (`D136569 <https://reviews.llvm.org/D136569>`_)
+* ``DT_RISCV_VARIANT_CC`` is now produced if at least one ``R_RISCV_JUMP_SLOT``
+  relocation references a symbol with the ``STO_RISCV_VARIANT_CC`` bit.
+  (`D107951 <https://reviews.llvm.org/D107951>`_)
 
 Breaking changes
 ----------------

lld/test/ELF/riscv-variant-cc.s

@@ -0,0 +1,128 @@
+# REQUIRES: riscv
+# RUN: rm -rf %t && split-file %s %t && cd %t
+
+# RUN: llvm-mc -filetype=obj -triple=riscv64 1.s -o 1.o
+# RUN: ld.lld 1.o --shared -o 1.so
+# RUN: llvm-readelf -d -s 1.so | FileCheck --check-prefix=CHECK1 %s
+
+# CHECK1:      Symbol table '.dynsym'
+# CHECK1:      0 NOTYPE GLOBAL DEFAULT [VARIANT_CC] [[#]] func_global_def
+# CHECK1:      Symbol table '.symtab'
+# CHECK1:      0 NOTYPE GLOBAL DEFAULT [VARIANT_CC] [[#]] func_global_def
+
+# RUN: llvm-mc -filetype=obj -triple=riscv64 2.s -o 2.o
+# RUN: ld.lld 2.o --shared -o 2.so
+# RUN: llvm-readelf -d -s 2.so | FileCheck --check-prefix=CHECK2 %s
+
+# CHECK2:      0x0000000070000001 (RISCV_VARIANT_CC) 0x0
+# CHECK2:      Symbol table '.dynsym'
+# CHECK2:      0 NOTYPE GLOBAL DEFAULT [VARIANT_CC] [[#]] func_global_def
+# CHECK2:      Symbol table '.symtab'
+# CHECK2:      0 NOTYPE GLOBAL DEFAULT [VARIANT_CC] [[#]] func_global_def
+
+# RUN: llvm-mc -filetype=obj -triple=riscv32 3.s -o 3.o
+# RUN: ld.lld 3.o --shared -o 3.so
+# RUN: llvm-readelf -d -s 3.so | FileCheck --check-prefix=CHECK3 %s
+
+# CHECK3:      0x70000001 (RISCV_VARIANT_CC) 0x0
+# CHECK3:      Symbol table '.dynsym'
+# CHECK3:      0 IFUNC  GLOBAL DEFAULT [VARIANT_CC] UND   ifunc_global_def
+# CHECK3:      0 NOTYPE GLOBAL DEFAULT               [[#]] func_global_def
+
+# RUN: llvm-mc -filetype=obj -triple=riscv32 4.s -o 4.o
+# RUN: ld.lld 4.o --shared -o 4.so
+# RUN: llvm-readelf -d -s 4.so | FileCheck --check-prefix=CHECK4 %s
+
+# CHECK4-NOT:  (RISCV_VARIANT_CC)
+# CHECK4:      Symbol table '.dynsym'
+# CHECK4:      0 IFUNC GLOBAL DEFAULT [VARIANT_CC]  [[#]] ifunc_global_def
+
+# RUN: llvm-mc -filetype=obj -triple=riscv64 5.s -o 5.o
+# RUN: ld.lld 5.o --shared -o 5.so
+# RUN: llvm-readelf -d -s 5.so | FileCheck --check-prefix=CHECK5 %s
+
+# CHECK5:      Symbol table '.dynsym' contains 4 entries:
+# CHECK5:      0 NOTYPE  GLOBAL DEFAULT [VARIANT_CC] UND   func_global_undef
+# CHECK5-NEXT: 0 NOTYPE  GLOBAL DEFAULT [VARIANT_CC] [[#]] func_global_def
+# CHECK5-NEXT: 0 IFUNC   GLOBAL DEFAULT [VARIANT_CC] [[#]] ifunc_global_def
+# CHECK5:      Symbol table '.symtab' contains 9 entries:
+# CHECK5:      0 NOTYPE  LOCAL  DEFAULT [VARIANT_CC] [[#]] func_local
+# CHECK5-NEXT: 0 IFUNC   LOCAL  DEFAULT [VARIANT_CC] [[#]] ifunc_local
+# CHECK5:      0 NOTYPE  LOCAL  HIDDEN  [VARIANT_CC] [[#]] func_global_hidden
+# CHECK5-NEXT: 0 IFUNC   LOCAL  HIDDEN  [VARIANT_CC] [[#]] ifunc_global_hidden
+# CHECK5:      0 NOTYPE  GLOBAL DEFAULT [VARIANT_CC] [[#]] func_global_def
+# CHECK5-NEXT: 0 NOTYPE  GLOBAL DEFAULT [VARIANT_CC] UND   func_global_undef
+# CHECK5-NEXT: 0 IFUNC   GLOBAL DEFAULT [VARIANT_CC] [[#]] ifunc_global_def
+
+#--- 1.s
+## An object with a variant_pcs symbol but without a R_RISCV_JMP_SLOT
+## should not generate a DT_RISCV_VARIANT_CC.
+.text
+.global func_global_def
+.variant_cc func_global_def
+
+func_global_def:
+  ret
+
+#--- 2.s
+## An object with a variant_cc symbol and with a R_RISCV_JMP_SLOT
+## should generate a DT_RISCV_VARIANT_CC.
+.text
+.global func_global_def
+.variant_cc func_global_def
+
+func_global_def:
+  call func_global_def
+
+#--- 3.s
+## Same as before, but targeting a GNU IFUNC.
+.text
+.global ifunc_global_def
+.global func_global_def
+.variant_cc ifunc_global_def
+.type ifunc_global_def, %gnu_indirect_function
+
+func_global_def:
+  call ifunc_global_def
+
+#--- 4.s
+## An object with a variant_cc symbol and with a R_RISCV_IRELATIVE
+## should not generate a DT_RISCV_VARIANT_CC.
+.text
+.global ifunc_global_def
+.global func_global_def
+.variant_cc ifunc_global_def
+.type ifunc_global_def, %gnu_indirect_function
+
+ifunc_global_def:
+  call func_global_def
+
+#--- 5.s
+## Check if STO_RISCV_VARIANT_CC is kept on symbol st_other for both undef,
+## local, and hidden visibility.
+.text
+.global func_global_def, func_global_undef, func_global_hidden
+.global ifunc_global_def, ifunc_global_hidden
+.local func_local
+
+.hidden func_global_hidden, ifunc_global_hidden
+
+.type ifunc_global_def, %gnu_indirect_function
+.type ifunc_global_hidden, %gnu_indirect_function
+.type ifunc_local, %gnu_indirect_function
+
+.variant_cc func_global_def
+.variant_cc func_global_undef
+.variant_cc func_global_hidden
+.variant_cc func_local
+.variant_cc ifunc_global_def
+.variant_cc ifunc_global_hidden
+.variant_cc ifunc_local
+
+func_global_def:
+func_global_hidden:
+func_local:
+ifunc_global_def:
+ifunc_global_hidden:
+ifunc_local:
+  ret