[lld][LoongArch] Support the R_LARCH_CALL36 relocation type

R_LARCH_CALL36 was designed for function call on medium code model
where the 2 instructions (pcaddu18i + jirl) must be adjacent. This is
expected to replace current medium code model implementation, i.e.
R_LARCH_PCALA_{HI20,LO12} on pcalau12i + jirl.

See loongson/la-abi-specs#3 for more details.

Author: SixWeining

lld/ELF/Arch/LoongArch.cpp

@@ -463,6 +463,7 @@ RelExpr LoongArch::getRelExpr(const RelType type, const Symbol &s,
   case R_LARCH_B16:
   case R_LARCH_B21:
   case R_LARCH_B26:
+  case R_LARCH_CALL36:
     return R_PLT_PC;
   case R_LARCH_GOT_PC_HI20:
   case R_LARCH_GOT64_PC_LO20:
@@ -590,6 +591,20 @@ void LoongArch::relocate(uint8_t *loc, const Relocation &rel,
     write32le(loc, setD10k16(read32le(loc), val >> 2));
     return;
 
+  case R_LARCH_CALL36: {
+    // This relocation type is designed for the adjancent pcaddu18i+jirl pair,
+    // so patch these 2 instructions in one time.
+    checkInt(loc, val, 38, rel);
+    checkAlignment(loc, val, 4, rel);
+    // Since jirl performs sign extension on the offset immediate, adds (1<<17)
+    // to original val to get the correct hi20.
+    uint32_t hi20 = extractBits(val + (1 << 17), 37, 18);
+    uint32_t lo18 = val & (1 << 18) - 1;
+    write32le(loc, setJ20(read32le(loc), hi20));
+    write32le(loc + 4, setK16(read32le(loc + 4), lo18 >> 2));
+    return;
+  }
+
   // Relocs intended for `addi`, `ld` or `st`.
   case R_LARCH_PCALA_LO12:
     // We have to again inspect the insn word to handle the R_LARCH_PCALA_LO12

lld/test/ELF/loongarch-call36-shared.s

@@ -0,0 +1,41 @@
+# REQUIRES: loongarch
+# RUN: rm -rf %t && split-file %s %t
+# RUN: llvm-mc --filetype=obj --triple=loongarch64-unknown-elf %t/a.s -o %t/a.o
+# RUN: ld.lld %t/a.o -shared -T %t/a.t -o %t/a.so
+# RUN: llvm-readelf -x .got.plt %t/a.so | FileCheck --check-prefix=GOTPLT %s
+# RUN: llvm-objdump -d --no-show-raw-insn %t/a.so | FileCheck %s
+
+## PLT should be present in this case.
+# CHECK:       Disassembly of section .plt:
+# CHECK:       <.plt>:
+##             bar@plt:
+# CHECK:       1234520:  pcaddu12i $t3, 64{{$}}
+# CHECK-NEXT:            ld.d $t3, $t3, 536{{$}}
+# CHECK-NEXT:            jirl $t1, $t3, 0
+# CHECK-NEXT:            nop
+
+# CHECK:      Disassembly of section .text:
+# CHECK:      <foo>:
+## hi20 = bar@plt - pc + (1 << 17) >> 18 = 0x1234520 - 0x1274670 + 0x20000 >> 18 = -1
+## lo18 = bar@plt - pc & (1 << 18) - 1 = 0x1234520 - 0x1274670 & 0x3ffff = -336
+# CHECK-NEXT: pcaddu18i $t0, -1{{$}}
+# CHECK-NEXT: jirl $zero, $t0, -336{{$}}
+
+# GOTPLT:      section '.got.plt':
+# GOTPLT-NEXT: 0x01274728 00000000 00000000 00000000 00000000
+# GOTPLT-NEXT: 0x01274738 00452301 00000000
+
+#--- a.t
+SECTIONS {
+ .plt   0x1234500: { *(.plt) }
+ .text  0x1274670: { *(.text) }
+}
+
+#--- a.s
+.text
+.global foo
+.global bar
+foo:
+    pcaddu18i $t0, 0
+    jirl      $zero, $t0, 0
+    .reloc foo, R_LARCH_CALL36, bar

lld/test/ELF/loongarch-call36.s

@@ -0,0 +1,40 @@
+# REQUIRES: loongarch
+
+# RUN: llvm-mc --filetype=obj --triple=loongarch64-unknown-elf %s -o %t.o
+
+# RUN: ld.lld %t.o --section-start=.text=0x20010 --section-start=.sec.foo=0x60020 -o %t1
+# RUN: llvm-objdump --no-show-raw-insn -d %t1 | FileCheck --match-full-lines %s --check-prefix=CASE1
+## hi20 = target - pc + (1 << 17) >> 18 = 0x60020 - 0x20010 + 0x20000 >> 18 = 1
+## lo18 = target - pc & (1 << 18) - 1 = 0x60020 - 0x20010 & 0x3ffff = 16
+# CASE1:      20010: pcaddu18i $ra, 1
+# CASE1-NEXT: 20014: jirl $zero, $ra, 16
+
+# RUN: ld.lld %t.o --section-start=.text=0x20010 --section-start=.sec.foo=0x40020 -o %t2
+# RUN: llvm-objdump --no-show-raw-insn -d %t2 | FileCheck --match-full-lines %s --check-prefix=CASE2
+## hi20 = target - pc + (1 << 17) >> 18 = 0x40020 - 0x20010 + 0x20000 >> 18 = 1
+## lo18 = target - pc & (1 << 18) - 1 = 0x40020 - 0x20010 & 0x3ffff = -131056
+# CASE2:      20010: pcaddu18i $ra, 1
+# CASE2-NEXT: 20014: jirl $zero, $ra, -131056
+
+# RUN: not ld.lld %t.o --section-start=.text=0x20000 --section-start=.sec.foo=0x2000020000 -o /dev/null 2>&1 | \
+# RUN:   FileCheck -DFILE=%t.o --check-prefix=ERROR-RANGE %s
+# ERROR-RANGE: error: [[FILE]]:(.text+0x0): relocation R_LARCH_CALL36 out of range: 137438953472 is not in [-137438953472, 137438953471]; references 'foo'
+
+## Impossible case in reality becasue all LoongArch instructions are fixed 4-bytes long.
+# RUN: not ld.lld %t.o --section-start=.text=0x20000 --section-start=.sec.foo=0x40001 -o /dev/null 2>&1 | \
+# RUN:   FileCheck -DFILE=%t.o --check-prefix=ERROR-ALIGN %s
+# ERROR-ALIGN: error: [[FILE]]:(.text+0x0): improper alignment for relocation R_LARCH_CALL36: 0x20001 is not aligned to 4 bytes
+
+.text
+.global _start
+_start:
+1:
+  pcaddu18i $ra, 0
+  jirl $zero, $ra, 0
+  .reloc 1b, R_LARCH_CALL36, foo
+
+.section .sec.foo,"ax"
+.global foo
+foo:
+  nop
+  ret