[llvm-branch-commits] [lld] release/21.x: [lld][LoongArch] Check that the relocation addend is zero before applying relaxation to R_LARCH_GOT_PC_{HI20, LO12} (#151264) (PR #151470)

[via llvm-branch-commits]

https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/151470

Backport 4ec8503e4c480f52426ddd03619b017f19a2f452

Requested by: @ylzsx

>From c07bf0b385b77327d370c9c5b0673df4bebccc97 Mon Sep 17 00:00:00 2001
From: Zhaoxin Yang <yangzhaoxin at loongson.cn>
Date: Wed, 30 Jul 2025 16:40:59 +0800
Subject: [PATCH] [lld][LoongArch] Check that the relocation addend is zero
 before applying relaxation to R_LARCH_GOT_PC_{HI20,LO12} (#151264)

Linker relaxation to R_LARCH_GOT_PC_{HI20,LO12} is only possible when
the addend of the relocation is zero.

Note: For `ld.bfd`, GOT references with non-zero addends will trigger an
assert in LoongArch, but `lld` handles these cases without any errors.
```
ld.bfd: BFD (GNU Binutils) 2.44.0 assertion fail
/usr/src/debug/binutils/binutils-gdb/bfd/elfnn-loongarch.c:4248
```

(cherry picked from commit 4ec8503e4c480f52426ddd03619b017f19a2f452)
---
 lld/ELF/Arch/LoongArch.cpp                  |  9 ++--
 lld/test/ELF/loongarch-relax-pc-hi20-lo12.s | 59 ++++++++++++++++-----
 2 files changed, 51 insertions(+), 17 deletions(-)

diff --git a/lld/ELF/Arch/LoongArch.cpp b/lld/ELF/Arch/LoongArch.cpp
index 15dcddb13baf7..a14553018fc36 100644
--- a/lld/ELF/Arch/LoongArch.cpp
+++ b/lld/ELF/Arch/LoongArch.cpp
@@ -809,10 +809,13 @@ static void relaxPCHi20Lo12(Ctx &ctx, const InputSection &sec, size_t i,
   // address.
   // Meanwhile skip undefined, preemptible and STT_GNU_IFUNC symbols, because
   // these symbols may be resolve in runtime.
+  // Moreover, relaxation can only occur if the addends of both relocations are
+  // zero for GOT references.
   if (rHi20.type == R_LARCH_GOT_PC_HI20 &&
-      (!rHi20.sym->isDefined() || rHi20.sym->isPreemptible ||
-       rHi20.sym->isGnuIFunc() ||
-       (ctx.arg.isPic && !cast<Defined>(*rHi20.sym).section)))
+      (!rHi20.sym || rHi20.sym != rLo12.sym || !rHi20.sym->isDefined() ||
+       rHi20.sym->isPreemptible || rHi20.sym->isGnuIFunc() ||
+       (ctx.arg.isPic && !cast<Defined>(*rHi20.sym).section) ||
+       rHi20.addend != 0 || rLo12.addend != 0))
     return;
 
   uint64_t dest = 0;
diff --git a/lld/test/ELF/loongarch-relax-pc-hi20-lo12.s b/lld/test/ELF/loongarch-relax-pc-hi20-lo12.s
index a417d89e9fa2e..a33f866506e13 100644
--- a/lld/test/ELF/loongarch-relax-pc-hi20-lo12.s
+++ b/lld/test/ELF/loongarch-relax-pc-hi20-lo12.s
@@ -1,22 +1,23 @@
 # REQUIRES: loongarch
+# RUN: rm -rf %t && split-file %s %t && cd %t
 
-# RUN: llvm-mc --filetype=obj --triple=loongarch32 -mattr=+relax %s -o %t.32.o
-# RUN: llvm-mc --filetype=obj --triple=loongarch64 -mattr=+relax %s -o %t.64.o
+# RUN: llvm-mc --filetype=obj --triple=loongarch32 -mattr=+relax a.s -o a.32.o
+# RUN: llvm-mc --filetype=obj --triple=loongarch64 -mattr=+relax a.s -o a.64.o
 
-# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x14000 %t.32.o -o %t.32
-# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x14000 %t.64.o -o %t.64
-# RUN: llvm-objdump -td --no-show-raw-insn %t.32 | FileCheck --check-prefixes=RELAX %s
-# RUN: llvm-objdump -td --no-show-raw-insn %t.64 | FileCheck --check-prefixes=RELAX %s
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x14000 a.32.o -o a.32
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x14000 a.64.o -o a.64
+# RUN: llvm-objdump -td --no-show-raw-insn a.32 | FileCheck --check-prefixes=RELAX %s
+# RUN: llvm-objdump -td --no-show-raw-insn a.64 | FileCheck --check-prefixes=RELAX %s
 
-# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x14000 %t.32.o -shared -o %t.32s
-# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x14000 %t.64.o -shared -o %t.64s
-# RUN: llvm-objdump -td --no-show-raw-insn %t.32s | FileCheck --check-prefixes=RELAX %s
-# RUN: llvm-objdump -td --no-show-raw-insn %t.64s | FileCheck --check-prefixes=RELAX %s
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x14000 a.32.o -shared -o a.32s
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x14000 a.64.o -shared -o a.64s
+# RUN: llvm-objdump -td --no-show-raw-insn a.32s | FileCheck --check-prefixes=RELAX %s
+# RUN: llvm-objdump -td --no-show-raw-insn a.64s | FileCheck --check-prefixes=RELAX %s
 
-# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x410000 %t.32.o -o %t.32o
-# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x410000 %t.64.o -o %t.64o
-# RUN: llvm-objdump -td --no-show-raw-insn %t.32o | FileCheck --check-prefixes=NORELAX32 %s
-# RUN: llvm-objdump -td --no-show-raw-insn %t.64o | FileCheck --check-prefixes=NORELAX64 %s
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x410000 a.32.o -o a.32o
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x410000 a.64.o -o a.64o
+# RUN: llvm-objdump -td --no-show-raw-insn a.32o | FileCheck --check-prefixes=NORELAX32 %s
+# RUN: llvm-objdump -td --no-show-raw-insn a.64o | FileCheck --check-prefixes=NORELAX64 %s
 
 # RELAX-LABEL: <_start>:
 ## offset = 0x14000 - 0x10000 = 4096<<2
@@ -49,6 +50,25 @@
 # NORELAX64-NEXT:          pcalau12i     $a0, 1024
 # NORELAX64-NEXT:          ld.d          $a0, $a0, 8
 
+
+## GOT references with non-zero addends. No relaxation.
+# RUN: llvm-mc --filetype=obj --triple=loongarch32 -mattr=+relax nonzero.s -o nonzero.32.o
+# RUN: llvm-mc --filetype=obj --triple=loongarch64 -mattr=+relax nonzero.s -o nonzero.64.o
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x14000 nonzero.32.o -o nonzero.32
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.data=0x14000 nonzero.64.o -o nonzero.64
+# RUN: llvm-objdump -td --no-show-raw-insn nonzero.32 | FileCheck --check-prefixes=NONZERO32 %s
+# RUN: llvm-objdump -td --no-show-raw-insn nonzero.64 | FileCheck --check-prefixes=NONZERO64 %s
+
+# NONZERO32-LABEL: <_start>:
+# NONZERO32-NEXT:      10000:  pcalau12i $a0, 4
+# NONZERO32-NEXT:              ld.w      $a0, $a0, 8
+
+# NONZERO64-LABEL: <_start>:
+# NONZERO64-NEXT:      10000:  pcalau12i $a0, 4
+# NONZERO64-NEXT:              ld.d      $a0, $a0, 12
+
+
+#--- a.s
 .section .text
 .global _start
 _start:
@@ -60,3 +80,14 @@ _start:
 .section .data
 sym:
   .zero 4
+
+
+#--- nonzero.s
+.section .text
+.global _start
+_start:
+  la.got    $a0, sym+4
+
+.section .data
+sym:
+  .zero 4