[flang] [libunwind] [llvm] [clang] [lldb] [libc] [clang-tools-extra] [compiler-rt] [libcxx] [lld] [ELF] Implement R_RISCV_TLSDESC for RISC-V (PR #79239)

[Fangrui Song via cfe-commits]

================
@@ -0,0 +1,125 @@
+# REQUIRES: riscv
+# RUN: rm -rf %t && split-file %s %t && cd %t
+# RUN: llvm-mc -filetype=obj -triple=riscv64 -mattr=+c,+relax a.s -o a.64.o
+# RUN: llvm-mc -filetype=obj -triple=riscv64 -mattr=+c,+relax c.s -o c.64.o
+# RUN: ld.lld -shared -soname=c.64.so c.64.o -o c.64.so
+
+# RUN: ld.lld -shared -z now a.64.o c.64.o -o a.64.so -z separate-code
+# RUN: llvm-objdump --no-show-raw-insn -M no-aliases -h -d a.64.so | FileCheck %s --check-prefix=GD64
+
+# RUN: ld.lld -e 0 -z now a.64.o c.64.o -o a.64.le -z separate-code
+# RUN: llvm-objdump --no-show-raw-insn -M no-aliases -h -d a.64.le | FileCheck %s --check-prefix=LE64
+
+# RUN: ld.lld -e 0 -z now a.64.o c.64.so -o a.64.ie -z separate-code
+# RUN: llvm-objdump --no-show-raw-insn -M no-aliases -h -d a.64.ie | FileCheck %s --check-prefix=IE64
+
+# GD64:      .got     00000018 00000000000020c0
+# GD64-LABEL: <_start>:
+# GD64-NEXT:         jal     {{.*}} <foo>
+# GD64-LABEL: <foo>:
+## &.got[c]-. = 0x20c0+8 - 0x1004 = 0x10c4
+# GD64:        1004: auipc   a2, 0x1
+# GD64-NEXT:         ld      a3, 0xc4(a2)
+# GD64-NEXT:         addi    a0, a2, 0xc4
+# GD64-NEXT:         jalr    t0, 0x0(a3)
+# GD64-NEXT:         c.add   a0, tp
+# GD64-NEXT:         jal     {{.*}} <foo>
+# GD64-NEXT:         auipc   a4, 0x1
+# GD64-NEXT:         ld      a5, 0xae(a4)
+# GD64-NEXT:         addi    a0, a4, 0xae
+# GD64-NEXT:         jalr    t0, 0x0(a5)
+# GD64-NEXT:         c.add   a0, tp
+
+# LE64-LABEL: <_start>:
+# LE64-NEXT:         jal     {{.*}} <foo>
+# LE64-LABEL: <foo>:
+# LE64-NEXT:  11004: lui     a0, 0x0
+# LE64-NEXT:         addi    a0, zero, 0xc
+# LE64-NEXT:         c.add   a0, tp
+# LE64-NEXT:         jal     {{.*}} <foo>
+# LE64-NEXT:         addi    zero, zero, 0x0
+# LE64-NEXT:         lui     a0, 0x0
+# LE64-NEXT:         addi    a0, zero, 0xc
+# LE64-NEXT:         c.add   a0, tp
+# LE64-NEXT:         addi    zero, zero, 0x0
+# LE64-NEXT:         lui     a0, 0x0
+# LE64-NEXT:         addi    a0, zero, 0xc
+# LE64-NEXT:         c.add   a0, tp
+
+# IE64:       .got     00000010 00000000000120e0
+# IE64-LABEL: <_start>:
+# IE64-NEXT:         jal     {{.*}} <foo>
+# IE64-LABEL: <foo>:
+## &.got[c]-. = 0x120e0+8 - 0x11004 = 0x10e4
+# IE64-NEXT:  11004: auipc   a0, 0x1
+# IE64-NEXT:         ld      a0, 0xe4(a0)
+# IE64-NEXT:         c.add   a0, tp
+# IE64-NEXT:         jal     {{.*}} <foo>
+# IE64-NEXT:         addi    zero, zero, 0x0
+## &.got[c]-. = 0x120e0+8 - 0x11016 = 0x10d2
+# IE64-NEXT:  11016: auipc   a0, 0x1
+# IE64-NEXT:         ld      a0, 0xd2(a0)
+# IE64-NEXT:         c.add   a0, tp
+# IE64-NEXT:         addi    zero, zero, 0x0
+## &.got[c]-. = 0x120e0+8 - 0x11024 = 0x10c4
+# IE64-NEXT:  11024: auipc   a0, 0x1
+# IE64-NEXT:         ld      a0, 0xc4(a0)
+# IE64-NEXT:         c.add   a0, tp
+
+#--- a.s
+.globl _start
+_start:
+.balign 16
+  call foo
+
+foo:
+.Ltlsdesc_hi0:
+.option norelax
+## All 4 instructions have an R_RISCV_RELAX.
+  auipc a2, %tlsdesc_hi(c)
+  .reloc .-4, R_RISCV_RELAX, 0
+  ld    a3, %tlsdesc_load_lo(.Ltlsdesc_hi0)(a2)
+  .reloc .-4, R_RISCV_RELAX, 0
+  addi  a0, a2, %tlsdesc_add_lo(.Ltlsdesc_hi0)
+  .reloc .-4, R_RISCV_RELAX, 0
+  jalr  t0, 0(a3), %tlsdesc_call(.Ltlsdesc_hi0)
+  .reloc .-4, R_RISCV_RELAX, 0
+  add   a0, a0, tp
----------------
MaskRay wrote:

Thanks for noticing this. `i386-tlsdesc-gd.s` has `movl %edx, %ebx  # GCC -O0 may add an extra insn in between.` that I forgot to copy here. Done.

This requires the following code to handle it.
```
+      // For HI20/LOAD_LO12, disable NOP conversion in the presence of
+      // R_RISCV_RELAX, in case an unrelated instruction follows the current
+      // instruction.
+      if ((rel.type == R_RISCV_TLSDESC_HI20 ||
+           rel.type == R_RISCV_TLSDESC_LOAD_LO12) &&
+          i + 1 != relocs.size() && relocs[i + 1].type == R_RISCV_RELAX)
+        continue;
```

https://github.com/llvm/llvm-project/pull/79239