[lld/ELF] Hint if R_X86_64_PC32 overflows and references a SHF_X86_64_LARGE section

[aeubanks]

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.

[llvmbot]

@llvm/pr-subscribers-lld-elf

@llvm/pr-subscribers-lld

Author: Arthur Eubanks (aeubanks)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/73045.diff

2 Files Affected:

• (modified) lld/ELF/Relocations.cpp (+6)
• (added) lld/test/ELF/x86-64-pc32-overflow-large.s (+25)

diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
index fe3d7f419e84aa6..37a2363094020d0 100644
--- a/lld/ELF/Relocations.cpp
+++ b/lld/ELF/Relocations.cpp
@@ -105,6 +105,12 @@ 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 (rel.type == R_X86_64_PC32 && rel.sym->getOutputSection() &&
+        (rel.sym->getOutputSection()->flags & SHF_X86_64_LARGE)) {
+      hint += "; a R_X86_64_PC32 relocation 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 000000000000000..54c20eddfd04c33
--- /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: {{.*}}; a R_X86_64_PC32 relocation 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) }
+}

[MaskRay]

In the diagnostic the sentence can be more precise. Perhaps ; R_X86_64_PC32 should not reference a section marked . In other messages we do use R_* to refer to a relocation of the type.