From 1d4c0092a82aa351c5a6e9e501cc5edbc6c0477f Mon Sep 17 00:00:00 2001
From: Arthur Eubanks <aeubanks@google.com>
Date: Wed, 17 Jan 2024 16:38:59 -0700
Subject: [PATCH] [lld/ELF] Hint if R_X86_64_PC32 overflows and references a
 SHF_X86_64_LARGE section (#73045)

Makes it clearer what the issue is when hand-written assembly doesn't
follow medium code model assumptions in a medium code model build.

Alternative to #71248 by only hinting on an overflow.
---
 lld/ELF/Relocations.cpp                   |  7 +++++++
 lld/test/ELF/x86-64-pc32-overflow-large.s | 25 +++++++++++++++++++++++
 2 files changed, 32 insertions(+)
 create mode 100644 lld/test/ELF/x86-64-pc32-overflow-large.s

diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
index af974d0f90e1d..59b0220795871 100644
--- a/lld/ELF/Relocations.cpp
+++ b/lld/ELF/Relocations.cpp
@@ -105,6 +105,13 @@ void elf::reportRangeError(uint8_t *loc, const Relocation &rel, const Twine &v,
       hint = "; references '" + lld::toString(*rel.sym) + '\'';
     else if (auto *d = dyn_cast<Defined>(rel.sym))
       hint = ("; references section '" + d->section->name + "'").str();
+
+    if (config->emachine == EM_X86_64 && rel.type == R_X86_64_PC32 &&
+        rel.sym->getOutputSection() &&
+        (rel.sym->getOutputSection()->flags & SHF_X86_64_LARGE)) {
+      hint += "; R_X86_64_PC32 should not reference a section marked "
+              "SHF_X86_64_LARGE";
+    }
   }
   if (!errPlace.srcLoc.empty())
     hint += "\n>>> referenced by " + errPlace.srcLoc;
diff --git a/lld/test/ELF/x86-64-pc32-overflow-large.s b/lld/test/ELF/x86-64-pc32-overflow-large.s
new file mode 100644
index 0000000000000..fb8f3e4480c40
--- /dev/null
+++ b/lld/test/ELF/x86-64-pc32-overflow-large.s
@@ -0,0 +1,25 @@
+# REQUIRES: x86
+# RUN: split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/a.s -o %t/a.o
+# RUN: not ld.lld %t/a.o -T %t/lds -o /dev/null 2>&1 | FileCheck %s
+
+# CHECK: error: {{.*}}a.o:(.text+{{.*}}): relocation R_X86_64_PC32 out of range: {{.*}}; R_X86_64_PC32 should not reference a section marked SHF_X86_64_LARGE
+
+#--- a.s
+.text
+.globl _start
+.type _start, @function
+_start:
+  movq hello(%rip), %rax
+
+.section ldata,"awl",@progbits
+.type   hello, @object
+.globl  hello
+hello:
+.long   1
+
+#--- lds
+SECTIONS {
+  .text 0x100000 : { *(.text) }
+  ldata 0x80200000 : { *(ldata) }
+}