[llvm] [Offload] Detect native ELF machine from preprocessor (PR #91282)

[Joseph Huber via llvm-commits]

https://github.com/jhuber6 updated https://github.com/llvm/llvm-project/pull/91282

>From 9d583b527ff12c9434200515123a9274fa9caec7 Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Mon, 6 May 2024 17:57:35 -0500
Subject: [PATCH] [Offload] Detect native ELF machine from preprocessor

Summary:
This gets the target's corresponding ELF value from the preprocessor.
We use this to detect if a given ELF is compatible with the CPU
offloading impolementation for OpenMP. Previously we used defitions from
CMake, but this is easier for people to understand as there may be new
users of this in the future.
---
 .../plugins-nextgen/common/include/Utils/ELF.h    |  3 +++
 offload/plugins-nextgen/common/src/Utils/ELF.cpp  | 15 +++++++++++++++
 offload/plugins-nextgen/host/CMakeLists.txt       |  5 -----
 offload/plugins-nextgen/host/src/rtl.cpp          | 10 ++++------
 4 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/offload/plugins-nextgen/common/include/Utils/ELF.h b/offload/plugins-nextgen/common/include/Utils/ELF.h
index 88c83d39b68ce..f87e0a5ed02b4 100644
--- a/offload/plugins-nextgen/common/include/Utils/ELF.h
+++ b/offload/plugins-nextgen/common/include/Utils/ELF.h
@@ -24,6 +24,9 @@ namespace elf {
 /// Returns true or false if the \p Buffer is an ELF file.
 bool isELF(llvm::StringRef Buffer);
 
+/// Returns the ELF e_machine value of the current compilation target.
+uint16_t getTargetMachine();
+
 /// Checks if the given \p Object is a valid ELF matching the e_machine value.
 llvm::Expected<bool> checkMachine(llvm::StringRef Object, uint16_t EMachine);
 
diff --git a/offload/plugins-nextgen/common/src/Utils/ELF.cpp b/offload/plugins-nextgen/common/src/Utils/ELF.cpp
index 2ae97f0f25892..90d6950b83e5a 100644
--- a/offload/plugins-nextgen/common/src/Utils/ELF.cpp
+++ b/offload/plugins-nextgen/common/src/Utils/ELF.cpp
@@ -36,6 +36,21 @@ bool utils::elf::isELF(StringRef Buffer) {
   }
 }
 
+uint16_t utils::elf::getTargetMachine() {
+#if defined(__x86_64__)
+  return EM_X86_64;
+#elif defined(__s390x__)
+  return EM_S390;
+#elif defined(__aarch64__)
+  return EM_AARCH64;
+#elif defined(__powerpc64__)
+  return EM_PPC64;
+#else
+#warning "Unknown ELF compilation target architecture"
+  return EM_NONE;
+#endif
+}
+
 template <class ELFT>
 static Expected<bool>
 checkMachineImpl(const object::ELFObjectFile<ELFT> &ELFObj, uint16_t EMachine) {
diff --git a/offload/plugins-nextgen/host/CMakeLists.txt b/offload/plugins-nextgen/host/CMakeLists.txt
index 48e591bc894e6..1d000442c84d4 100644
--- a/offload/plugins-nextgen/host/CMakeLists.txt
+++ b/offload/plugins-nextgen/host/CMakeLists.txt
@@ -52,27 +52,22 @@ endif()
 
 # Define the target specific triples and ELF machine values.
 if(CMAKE_SYSTEM_PROCESSOR MATCHES "ppc64le$")
-  target_compile_definitions(omptarget.rtl.host PRIVATE TARGET_ELF_ID=EM_PPC64)
   list(APPEND LIBOMPTARGET_SYSTEM_TARGETS 
        "powerpc64le-ibm-linux-gnu" "powerpc64le-ibm-linux-gnu-LTO")
   set(LIBOMPTARGET_SYSTEM_TARGETS "${LIBOMPTARGET_SYSTEM_TARGETS}" PARENT_SCOPE)
 elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "ppc64$")
-  target_compile_definitions(omptarget.rtl.host PRIVATE TARGET_ELF_ID=EM_PPC64)
   list(APPEND LIBOMPTARGET_SYSTEM_TARGETS 
        "powerpc64-ibm-linux-gnu" "powerpc64-ibm-linux-gnu-LTO")
   set(LIBOMPTARGET_SYSTEM_TARGETS "${LIBOMPTARGET_SYSTEM_TARGETS}" PARENT_SCOPE)
 elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "x86_64$")
-  target_compile_definitions(omptarget.rtl.host PRIVATE TARGET_ELF_ID=EM_X86_64)
   list(APPEND LIBOMPTARGET_SYSTEM_TARGETS 
        "x86_64-pc-linux-gnu" "x86_64-pc-linux-gnu-LTO")
   set(LIBOMPTARGET_SYSTEM_TARGETS "${LIBOMPTARGET_SYSTEM_TARGETS}" PARENT_SCOPE)
 elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "aarch64$")
-  target_compile_definitions(omptarget.rtl.host PRIVATE TARGET_ELF_ID=EM_AARCH64)
   list(APPEND LIBOMPTARGET_SYSTEM_TARGETS 
        "aarch64-unknown-linux-gnu" "aarch64-unknown-linux-gnu-LTO")
   set(LIBOMPTARGET_SYSTEM_TARGETS "${LIBOMPTARGET_SYSTEM_TARGETS}" PARENT_SCOPE)
 elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "s390x$")
-  target_compile_definitions(omptarget.rtl.host PRIVATE TARGET_ELF_ID=EM_S390)
   list(APPEND LIBOMPTARGET_SYSTEM_TARGETS 
        "s390x-ibm-linux-gnu" "s390x-ibm-linux-gnu-LTO")
   set(LIBOMPTARGET_SYSTEM_TARGETS "${LIBOMPTARGET_SYSTEM_TARGETS}" PARENT_SCOPE)
diff --git a/offload/plugins-nextgen/host/src/rtl.cpp b/offload/plugins-nextgen/host/src/rtl.cpp
index c929db6c22d83..4bdcae3dd6a1b 100644
--- a/offload/plugins-nextgen/host/src/rtl.cpp
+++ b/offload/plugins-nextgen/host/src/rtl.cpp
@@ -18,6 +18,7 @@
 
 #include "Shared/Debug.h"
 #include "Shared/Environment.h"
+#include "Utils/ELF.h"
 
 #include "GlobalHandler.h"
 #include "OpenMP/OMPT/Callback.h"
@@ -44,11 +45,6 @@
 // The number of devices in this plugin.
 #define NUM_DEVICES 4
 
-// The ELF ID should be defined at compile-time by the build system.
-#ifndef TARGET_ELF_ID
-#define TARGET_ELF_ID EM_NONE
-#endif
-
 namespace llvm {
 namespace omp {
 namespace target {
@@ -416,7 +412,9 @@ struct GenELF64PluginTy final : public GenericPluginTy {
   }
 
   /// Get the ELF code to recognize the compatible binary images.
-  uint16_t getMagicElfBits() const override { return ELF::TARGET_ELF_ID; }
+  uint16_t getMagicElfBits() const override {
+    return utils::elf::getTargetMachine();
+  }
 
   /// This plugin does not support exchanging data between two devices.
   bool isDataExchangable(int32_t SrcDeviceId, int32_t DstDeviceId) override {