[lld] [lld][LoongArch] Support the R_LARCH_{ADD, SUB}6 relocation type (PR #72190)

[Jinyang He via llvm-commits]

https://github.com/MQ-mengqing created https://github.com/llvm/llvm-project/pull/72190

The R_LARCH_{ADD,SUB}6 relocation type are usually used by DwarfCFA to calculate a tiny offset. They appear after binutils 2.41, with GAS enable relaxation by default.

>From b489a3c9853fefef12af8511a3d473e96053f2ff Mon Sep 17 00:00:00 2001
From: Jinyang He <hejinyang at loongson.cn>
Date: Mon, 9 Oct 2023 09:18:45 +0800
Subject: [PATCH] [lld][LoongArch] Support the R_LARCH_{ADD,SUB}6 relocation
 type

The R_LARCH_{ADD,SUB}6 relocation type are usually used by DwarfCFA to
calculate a tiny offset. They appear after binutils 2.41, with GAS
enable relaxation by default.
---
 lld/ELF/Arch/LoongArch.cpp       | 8 ++++++++
 lld/test/ELF/loongarch-add-sub.s | 6 +++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/lld/ELF/Arch/LoongArch.cpp b/lld/ELF/Arch/LoongArch.cpp
index 04ddb4682917b4b..d3a538577a59a5d 100644
--- a/lld/ELF/Arch/LoongArch.cpp
+++ b/lld/ELF/Arch/LoongArch.cpp
@@ -444,10 +444,12 @@ RelExpr LoongArch::getRelExpr(const RelType type, const Symbol &s,
   case R_LARCH_TLS_LE64_LO20:
   case R_LARCH_TLS_LE64_HI12:
     return R_TPREL;
+  case R_LARCH_ADD6:
   case R_LARCH_ADD8:
   case R_LARCH_ADD16:
   case R_LARCH_ADD32:
   case R_LARCH_ADD64:
+  case R_LARCH_SUB6:
   case R_LARCH_SUB8:
   case R_LARCH_SUB16:
   case R_LARCH_SUB32:
@@ -650,6 +652,9 @@ void LoongArch::relocate(uint8_t *loc, const Relocation &rel,
     write32le(loc, setK12(read32le(loc), extractBits(val, 63, 52)));
     return;
 
+  case R_LARCH_ADD6:
+    *loc = (*loc & 0xc0) | ((*loc + val) & 0x3f);
+    return;
   case R_LARCH_ADD8:
     *loc += val;
     return;
@@ -662,6 +667,9 @@ void LoongArch::relocate(uint8_t *loc, const Relocation &rel,
   case R_LARCH_ADD64:
     write64le(loc, read64le(loc) + val);
     return;
+  case R_LARCH_SUB6:
+    *loc = (*loc & 0xc0) | ((*loc - val) & 0x3f);
+    return;
   case R_LARCH_SUB8:
     *loc -= val;
     return;
diff --git a/lld/test/ELF/loongarch-add-sub.s b/lld/test/ELF/loongarch-add-sub.s
index 63a3f7de179e6b8..35f8a053d69cef3 100644
--- a/lld/test/ELF/loongarch-add-sub.s
+++ b/lld/test/ELF/loongarch-add-sub.s
@@ -6,7 +6,7 @@
 # RUN: llvm-readelf -x .rodata %t.la64 | FileCheck --check-prefix=CHECK %s
 # CHECK:      section '.rodata':
 # CHECK-NEXT: 0x9876543210 10325476 98badcfe 804602be 79ffffff
-# CHECK-NEXT: 0x9876543220 804602be 804680
+# CHECK-NEXT: 0x9876543220 804602be 80468097
 
 .text
 .global _start
@@ -34,3 +34,7 @@ quux:
     .byte 0
     .reloc quux, R_LARCH_ADD8, 1b
     .reloc quux, R_LARCH_SUB8, 2b
+qux:
+    .byte 0b10000000
+    .reloc qux, R_LARCH_ADD6, qux
+    .reloc qux, R_LARCH_SUB6, 2b