Support R_LARCH_CALL36

elf/arch-loongarch.cc

@@ -471,6 +471,20 @@ void InputSection<E>::apply_reloc_alloc(Context<E> &ctx, u8 *base) {
     case R_LARCH_64_PCREL:
       *(ul64 *)loc = S + A - P;
       break;
+    case R_LARCH_CALL36:
+      if (removed_bytes == 0) {
+        write_j20(loc, (S + A - P + 0x20000) >> 18);
+        write_k16(loc + 4, (S + A - P) >> 2);
+      } else {
+        // Rewrite PCADDU18I + JIRL to B or BL
+        assert(removed_bytes == 4);
+        if (get_rd(*(ul32 *)(contents.data() + rel.r_offset + 4)) == 0)
+          *(ul32 *)loc = 0x5000'0000; // B
+        else
+          *(ul32 *)loc = 0x5400'0000; // BL
+        write_k16(loc, (S + A - P) >> 2);
+      }
+      break;
     case R_LARCH_ADD_ULEB128:
       overwrite_uleb(loc, read_uleb(loc) + S + A);
       break;
@@ -626,6 +640,7 @@ void InputSection<E>::scan_relocations(Context<E> &ctx) {
       break;
     case R_LARCH_B26:
     case R_LARCH_PCALA_HI20:
+    case R_LARCH_CALL36:
       if (sym.is_imported)
         sym.flags |= NEEDS_PLT;
       break;
@@ -792,6 +807,21 @@ void shrink_section(Context<E> &ctx, InputSection<E> &isec, bool use_rvc) {
           delta += 4;
       }
       break;
+    case R_LARCH_CALL36:
+      // A CALL36 relocation referes to the following instruction pair
+      // to jump to PC ± 128 GiB.
+      //
+      //   pcaddu18i $t0,       0         # R_LARCH_CALL36
+      //   jirl      $zero/$ra, $t0, 0
+      //
+      // If the displacement is PC ± 128 MiB, we can use B or BL instead.
+      // Note that $zero is $r0 and $ra is $r1.
+      if (i64 dist = compute_distance(ctx, sym, isec, r);
+          -(1 << 27) <= dist && dist < (1 << 27))
+        if (u32 jirl = *(ul32 *)(isec.contents.data() + rels[i].r_offset + 4);
+            get_rd(jirl) == 0 || get_rd(jirl) == 1)
+          delta += 4;
+      break;
     }
   }
 

test/elf/loongarch64_relax-call36.sh

@@ -0,0 +1,47 @@
+#!/bin/bash
+. $(dirname $0)/common.inc
+
+cat <<'EOF' | $CC -o $t/a.o -c -xassembler -
+.globl foo, bar
+foo:
+  move      $s0,   $ra
+  .reloc ., R_LARCH_CALL36, foo2
+  .reloc ., R_LARCH_RELAX
+  pcaddu18i $t0,   0
+  jirl      $ra,   $t0, 0
+  move      $ra,   $s0
+  ret
+bar:
+  .reloc ., R_LARCH_CALL36, bar2
+  .reloc ., R_LARCH_RELAX
+  pcaddu18i $t0,   0
+  jirl      $zero, $t0, 0
+EOF
+
+cat <<EOF | $CC -o $t/b.o -c -xc -
+#include <stdio.h>
+void foo();
+void bar();
+void foo2() { printf("foo"); }
+void bar2() { printf("bar"); }
+
+int main() {
+  foo();
+  bar();
+  printf("\n");
+}
+EOF
+
+$CC -B. -o $t/exe1 $t/a.o $t/b.o -Wl,--no-relax
+$QEMU $t/exe1 | grep -q foobar
+
+$OBJDUMP -d $t/exe1 > $t/exe1.objdump
+grep -A2 '<foo>:' $t/exe1.objdump | grep -wq pcaddu18i
+grep -A2 '<bar>:' $t/exe1.objdump | grep -wq pcaddu18i
+
+$CC -B. -o $t/exe2 $t/a.o $t/b.o -Wl,--relax
+$QEMU $t/exe2 | grep -q foobar
+
+$OBJDUMP -d $t/exe2 > $t/exe2.objdump
+grep -A2 '<foo>:' $t/exe2.objdump | grep -wq bl
+grep -A2 '<bar>:' $t/exe2.objdump | grep -wq b