Use inline assembly

DataDog · zhengyu123 · Jul 18, 2025 · Jul 14, 2025 · Jul 15, 2025 · Jul 15, 2025
commit 33261bcefbc38e26d70cd67f33995e1dee5c5fb6
diff --git a/ddprof-lib/build.gradle b/ddprof-lib/build.gradle
@@ -516,19 +516,15 @@ tasks.whenTaskAdded { task ->
             onlyIf {
               config.active
             }
-
             group = 'build'
             description = "Link the ${config.name} build of the library"
             source = fileTree("$buildDir/obj/main/${config.name}")
-            source.from(file("${projectDir}/build/obj/main/asm/assembly.o"))
 
             linkedFile = file("$buildDir/lib/main/${config.name}/${osIdentifier()}/${archIdentifier()}/libjavaProfiler.${os().isLinux() ? 'so' : 'dylib'}")
             def compileTask = tasks.findByName("compileLib${config.name.capitalize()}".toString())
             if (compileTask != null) {
               dependsOn compileTask
             }
-            def asmTask = tasks.findByName("asm")
-            dependsOn asmTask
             linkerArgs.addAll(config.linkerArgs)
             toolChain = task.toolChain
             targetPlatform = task.targetPlatform
@@ -609,45 +605,6 @@ tasks.register('javadocJar', Jar) {
   from javadoc.destinationDir
 }
 
-tasks.register('asm', Exec) {
-  group = 'build'
-
-  def arch
-  if (archIdentifier() == 'x64') {
-    arch = '-D__x86_64__'
-  } else {
-    arch = '-D__aarch64__'
-  }
-
-  def os
-  if (osIdentifier() == 'macos') {
-    os = '-D__APPLE__'
-  } else {
-    os = '-D__LINUX__'
-  }
-  def asmDir = file("${projectDir}/src/main/assembler")
-  if (!asmDir.exists()) {
-    // no assembler files found, skipping
-    return
-  }
-
-  doLast {
-    // Ensure the output directory exists
-    file("${projectDir}/build/obj/main/asm").mkdirs()
-  }
-
-  // collect all assembler files and compile them
-  workingDir asmDir
-  inputs.files fileTree("${projectDir}/src/main/assembler") {
-    include '**/*.S'
-  }
-  def asmFiles = inputs.files.collect { it.absolutePath }
-  outputs.dir "${projectDir}/build/obj/main/asm"
-  // use gcc to compile assembler files
-  commandLine 'gcc', arch, os, '-c', '-x', 'assembler-with-cpp',
-  *asmFiles, '-o', "${projectDir}/build/obj/main/asm/assembly.o"
-}
-
 tasks.register('scanBuild', Exec) {
   workingDir "${projectDir}/src/test/make"
   commandLine 'scan-build'

diff --git a/ddprof-lib/gtest/build.gradle b/ddprof-lib/gtest/build.gradle
@@ -154,10 +154,7 @@ tasks.whenTaskAdded { task ->
             group = 'verification'
             description = "Run all Google Tests for the ${config.name} build of the library"
           }
-          def libProject = project(':ddprof-lib')
-          def asmTask = libProject.tasks.findByName("asm")
-
-          libProject.file("src/test/cpp/").eachFile {
+          project(':ddprof-lib').file("src/test/cpp/").eachFile {
 
             def testFile = it
             def testName = it.name.substring(0, it.name.lastIndexOf('.'))
@@ -170,7 +167,6 @@ tasks.whenTaskAdded { task ->
               group = 'build'
               description = "Link the Google Test for the ${config.name} build of the library"
               source = fileTree("$buildDir/obj/gtest/${config.name}/${testName}")
-              source.from(file("${rootDir}/ddprof-lib/build/obj/main/asm/assembly.o"))
               linkedFile = binary
               if (config.name != 'release') {
                 // linking the gtests using the minimizing release flags is making gtest unhappy
@@ -187,7 +183,6 @@ tasks.whenTaskAdded { task ->
               libs = task.libs
               inputs.files source
               outputs.file linkedFile
-              dependsOn asmTask
             }
             def gtestExecuteTask = tasks.register("gtest${config.name.capitalize()}_${testName}", Exec) {
               onlyIf {

diff --git a/ddprof-lib/src/main/assembler/safefetch.S b/ddprof-lib/src/main/assembler/safefetch.S
@@ -34,15 +34,74 @@
     #endif
 #endif
 
-extern "C" char _SafeFetch32_continuation[] __attribute__ ((visibility ("hidden")));
-extern "C" char _SafeFetch32_fault[] __attribute__ ((visibility ("hidden")));
+#if defined(__x86_64__)
+  #ifdef __APPLE__
+    asm(R"(
+        .globl _safefetch32_impl
+        .private_extern _safefetch32_impl
+        _safefetch32_impl:
+            movl (%rdi), %eax
+            ret
+        .globl _safefetch32_continuation
+        .private_extern _safefetch32_continuation
+        _safefetch32_continuation:
+            movl %esi, %eax
+            ret
+    )");
+  #else
+    asm(R"(
+        .globl safefetch32_impl
+        .hidden safefetch32_impl
+        .type safefetch32_imp, %function
+        safefetch32_impl:
+            movl (%rdi), %eax
+            ret
+        .globl safefetch32_continuation
+        .hidden safefetch32_continuation
+        .type safefetch32_continuation, %function
+        safefetch32_continuation:
+            movl %esi, %eax
+            ret
+    )");
+  #endif // __APPLE__
+#elif defined(__aarch64__)
+  #ifdef __APPLE__
+    asm(R"(
+        .globl _safefetch32_impl
+        .private_extern _safefetch32_impl
+        _safefetch32_impl:
+            ldr      w0, [x0]
+            ret
+        .globl _safefetch32_continuation
+        .private_extern _safefetch32_continuation
+        _safefetch32_continuation:
+            mov      x0, x1
+            ret
+    )");
+  #else
+    asm(R"(
+        .globl safefetch32_impl
+        .hidden safefetch32_impl
+        .type safefetch32_impl, %function
+        safefetch32_impl:
+            ldr      w0, [x0]
+            ret
+        .globl safefetch32_continuation
+        .hidden safefetch32_continuation
+        .type safefetch32_continuation, %function
+        safefetch32_continuation:
+            mov      x0, x1
+            ret
+    )");
+  #endif
+#endif
 
 bool SafeAccess::handle_safefetch(int sig, void* context) {
   ucontext_t* uc = (ucontext_t*)context;
   uintptr_t pc = uc->context_pc;
   if ((sig == SIGSEGV || sig == SIGBUS) && uc != nullptr) {
-    if (pc == (uintptr_t)_SafeFetch32_fault) {
-      uc->context_pc = (uintptr_t)_SafeFetch32_continuation;
+    if (pc == (uintptr_t)safefetch32_impl) {
+      uc->context_pc = (uintptr_t)safefetch32_continuation;
       return true;
     }
   }

@@ -22,7 +22,8 @@
 #include <cassert>
 #include <stdint.h>
 
-extern "C" int SafeFetch32_impl(int* adr, int errValue);
+extern "C" int safefetch32_impl(int* adr, int errValue);
+extern "C" int safefetch32_continuation(int* adr, int errValue);
 
 #ifdef __clang__
 #define NOINLINE __attribute__((noinline))
@@ -35,7 +36,7 @@ class SafeAccess {
 public:
 
   static inline int safeFetch32(int* ptr, int errorValue) {
-    return SafeFetch32_impl(ptr, errorValue);
+    return safefetch32_impl(ptr, errorValue);
   }
 
   static bool handle_safefetch(int sig, void* context);