Session object: Set OS/ABI

This adapts LLVM's behavior of MCELFObjectTargetWriter::getOSABI [1].

[1]: 8c8a2679a2/llvm/include/llvm/MC/MCELFObjectWriter.h (L72-L86)

Cargo.lock

@@ -1688,6 +1688,7 @@ version = "0.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8c21d40587b92fa6a6c6e3c1bdbf87d75511db5672f9c93175574b3a00df1758"
 dependencies = [
+ "ahash",
  "compiler_builtins",
  "rustc-std-workspace-alloc",
  "rustc-std-workspace-core",
@@ -2539,6 +2540,18 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "object"
+version = "0.29.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "21158b2c33aa6d4561f1c0a6ea283ca92bc54802a93b263e910746d679a7eb53"
+dependencies = [
+ "crc32fast",
+ "hashbrown 0.12.0",
+ "indexmap",
+ "memchr",
+]
+
 [[package]]
 name = "odht"
 version = "0.3.1"
@@ -3664,7 +3677,7 @@ dependencies = [
  "itertools",
  "jobserver",
  "libc",
- "object 0.28.4",
+ "object 0.29.0",
  "pathdiff",
  "regex",
  "rustc_apfloat",

compiler/rustc_codegen_ssa/Cargo.toml

@@ -41,6 +41,6 @@ rustc_target = { path = "../rustc_target" }
 rustc_session = { path = "../rustc_session" }
 
 [dependencies.object]
-version = "0.28.4"
+version = "0.29.0"
 default-features = false
 features = ["read_core", "elf", "macho", "pe", "unaligned", "archive", "write"]

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -171,7 +171,15 @@ pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static
         }
         _ => 0,
     };
-    file.flags = FileFlags::Elf { e_flags };
+    // adapted from LLVM's `MCELFObjectTargetWriter::getOSABI`
+    let os_abi = match sess.target.options.os.as_ref() {
+        "hermit" => elf::ELFOSABI_STANDALONE,
+        "freebsd" => elf::ELFOSABI_FREEBSD,
+        "solaris" => elf::ELFOSABI_SOLARIS,
+        _ => elf::ELFOSABI_NONE,
+    };
+    let abi_version = 0;
+    file.flags = FileFlags::Elf { os_abi, abi_version, e_flags };
     Some(file)
 }