fix: error on R_X86_64_32/32S relocations in shared objects (#2074)

R_X86_64_32 and R_X86_64_32S cannot be used when making a shared
object because the dynamic linker has no way to patch 32-bit absolute
relocations at runtime. Wild was silently emitting R_X86_64_64 instead
of erroring, producing a broken shared object.

Add an early check in apply_relocation to error when these relocation
types are encountered while building a shared object, matching the
behavior of GNU ld and lld.

Also add ExpectErrorWild test directive (analogous to ExpectWarningWild)
to allow testing Wild-specific error messages independently.

Fixes #2074

Author: deepakshirkem

libwild/src/elf_writer.rs

@@ -2899,6 +2899,16 @@ fn apply_relocation<
                 .write_to_buffer(value, &mut out[offset_in_section as usize..])?;
             return Ok(RelocationModifier::Normal);
         }
+        RelocationKind::Absolute
+            if layout.symbol_db.output_kind.is_shared_object()
+                && matches!(r_type, object::elf::R_X86_64_32 | object::elf::R_X86_64_32S) =>
+        {
+            bail!(
+                "relocation type {} cannot be used when making a shared object; \
+                 recompile with -fPIC",
+                A::rel_type_to_string(r_type)
+            );
+        }
         _ => {}
     }
     let (resolution, symbol_index, local_symbol_id) = get_resolution(rel, object_layout, layout)?;

wild/tests/integration_tests.rs

@@ -120,6 +120,8 @@
 //!
 //! ExpectWarningWild:{message regex} As for ExpectWarning, but only checks Wild's warning output.
 //!
+//! ExpectErrorWild:{error regex} As for ExpectError, but only checks Wild's error output.
+//!
 //! Malfunction:{malfunction-id} Run with the specified malfunction enabled. Linking should still
 //! succeed, but linker-diff should report a diff. That diff will be snapshot tested.
 //!
@@ -1756,6 +1758,13 @@ fn process_directive(
             config.should_run = false;
             config.should_diff = false;
         }
+        "ExpectErrorWild" => {
+            config.expect_stderr.push(ErrorMatcher::wild_only(arg)?);
+            config.should_error = true;
+            // If there are errors, then there's nothing to run and nothing to diff.
+            config.should_run = false;
+            config.should_diff = false;
+        }
         "ExpectMessage" => {
             config.expect_stdout.push(ErrorMatcher::new(arg)?);
         }

wild/tests/sources/elf/pic-required/pic-required.s

@@ -0,0 +1,10 @@
+// Test that R_X86_64_32 cannot be used when making a shared object.
+// .long _shared generates R_X86_64_32 which is illegal in shared objects.
+// Both GNU ld and lld error: recompile with -fPIC
+//#Arch:x86_64
+//#LinkArgs:--no-gc-sections -shared
+//#ExpectError:recompile with -fPIC
+//#ExpectErrorWild:R_X86_64_32.*cannot be used when making a shared object
+
+.data
+.long _shared