Fix dlsym issue (#6048 => hotfix) (#6049)

## Summary of changes

This PR addresses the issue
#6045

## Reason for change

When using the `dlsym` function, the compiler adds in the import symbols
table that we need the `dlsym` symbol.
Before being a universal binary (same binary used for glibc-based linux
and musl-libc-based linux) and the compiler added in a `DT_NEEDED`
section the library `libdl.so` (the library containing `dlsym`). When
the wrapper is loaded, it will look through all the `DT_NEEDED` sections
to find a library that contains the `dlsym` symbol. Since being a
universal binary, the `DT_NEEDED` sections are removed (part of being
universal) and we have to resolve by hand needed symbols (`dlsym`,
`pthread_once` ..).
If we use `dlsym` (or other symbol), we will hit this issue.

## Implementation details

- use `__dd_dlsym` instead

## Test coverage

Added a snapshot test using `nm` that verifies that the undefined
symbols in the universal binary haven't changed. It's equivalent to
running

```bash
nm -D Datadog.Linux.ApiWrapper.x64.so | grep ' U ' | awk '{print $2}' | sed 's/@.*//' | sort
```

but done using Nuke instead. It would probably make sense for this to be
a "normal" test in the native tests, but given it has a dependency on
`nm`, which is _definitely_ available in the universal build dockerfile
it was quicker and easier to get this up and running directly. When it
fails, it prints the diff and throws an exception, e.g.

```bash
System.Exception: Found differences in undefined symbols (dlsym) in the Native Wrapper library. Verify that these changes are expected, and will not cause problems. Removing symbols is generally a safe operation, but adding them could cause crashes. If the new symbols are safe to add, update the snapshot file at C:\repos\dd-trace-dotnet\tracer\test\snapshots\native-wrapper-symbols-x64.verified.txt with the new values
```

## Other details

This is a hotfix for 
- #6048

Co-authored-by: Gregory LEOCADIE <gregory.leocadie@datadoghq.com>

.nuke/build.schema.json

@@ -477,6 +477,7 @@
               "SignDlls",
               "SignMsi",
               "SummaryOfSnapshotChanges",
+              "TestNativeWrapper",
               "UpdateChangeLog",
               "UpdateSnapshots",
               "UpdateSnapshotsFromBuild",
@@ -698,6 +699,7 @@
               "SignDlls",
               "SignMsi",
               "SummaryOfSnapshotChanges",
+              "TestNativeWrapper",
               "UpdateChangeLog",
               "UpdateSnapshots",
               "UpdateSnapshotsFromBuild",

profiler/src/ProfilerEngine/Datadog.Linux.ApiWrapper/functions_to_wrap.c

@@ -209,8 +209,8 @@ void initLibrary(void)
 
     // Bash provides its own version of the getenv/setenv functions
     // Fetch the original ones and use those instead
-    char *(*real_getenv)(const char *) = (char *(*)(const char *))dlsym(RTLD_NEXT, "getenv");
-    int (*real_setenv)(const char *, const char *, int) = (int (*)(const char *, const char *, int))dlsym(RTLD_NEXT, "setenv");
+    char *(*real_getenv)(const char *) = __dd_dlsym(RTLD_NEXT, "getenv");
+    int (*real_setenv)(const char *, const char *, int) = __dd_dlsym(RTLD_NEXT, "setenv");
 
     if (real_getenv == NULL || real_setenv == NULL)
     {

tracer/build/_build/Build.Profiler.Steps.cs

@@ -17,6 +17,7 @@
 using Nuke.Common.Utilities;
 using System.Collections;
 using System.Threading.Tasks;
+using DiffMatchPatch;
 using Logger = Serilog.Log;
 
 partial class Build
@@ -137,6 +138,84 @@ partial class Build
                 arguments: $"--build {NativeBuildDirectory} --parallel {Environment.ProcessorCount} --target wrapper");
         });
 
+    Target TestNativeWrapper => _ => _
+        .Unlisted()
+        .Description("Test that the Native wrapper symbols haven't changed")
+        .After(CompileNativeWrapper)
+        .OnlyWhenStatic(() => IsLinux)
+        .Executes(() =>
+        {
+            var (arch, _) = GetUnixArchitectureAndExtension();
+            var libraryPath = ProfilerDeployDirectory / arch / LinuxApiWrapperLibrary;
+
+            var output = Nm.Value($"-D {libraryPath}").Select(x => x.Text).ToList();
+
+            // Gives output similar to this:
+            // 0000000000006bc8 D DdDotnetFolder
+            // 0000000000006bd0 D DdDotnetMuslFolder
+            //                  w _ITM_deregisterTMCloneTable
+            //                  w _ITM_registerTMCloneTable
+            //                  w __cxa_finalize
+            //                  w __deregister_frame_info
+            //                  U __errno_location
+            //                  U __tls_get_addr
+            // 0000000000002d1b T _fini
+            // 0000000000002d18 T _init
+            // 0000000000003d70 T accept
+            // 0000000000003e30 T accept4
+            //                  U access
+            //
+            // The types of symbols are:
+            // D: Data section symbol. These symbols are initialized global variables.
+            // w: Weak symbol. These symbols are weakly referenced and can be overridden by other symbols.
+            // U: Undefined symbol. These symbols are referenced in the file but defined elsewhere.
+            // T: Text section symbol. These symbols are functions or executable code.
+            // B: BSS (Block Started by Symbol) section symbol. These symbols are uninitialized global variables.
+            //
+            // We only care about the Undefined symbols - we don't want to accidentally add more of them
+
+            Logger.Debug("NM output: {Output}", string.Join(Environment.NewLine, output));
+
+            var symbols = output
+                .Select(x => x.Trim())
+                .Where(x => x.StartsWith("U "))
+                .Select(x => x.TrimStart("U "))
+                .OrderBy(x => x)
+                .ToList();
+
+
+            var received = string.Join(Environment.NewLine, symbols);
+            var verifiedPath = TestsDirectory / "snapshots" / $"native-wrapper-symbols-{UnixArchitectureIdentifier}.verified.txt";
+            var verified = File.Exists(verifiedPath)
+                ? File.ReadAllText(verifiedPath)
+                : string.Empty;
+
+            Logger.Information("Comparing snapshot of Undefined symbols in the Native Wrapper library using {Path}...", verifiedPath);
+
+            var dmp = new diff_match_patch();
+            var diff = dmp.diff_main(verified, received);
+            dmp.diff_cleanupSemantic(diff);
+
+            var changedSymbols = diff
+                .Where(x => x.operation != Operation.EQUAL)
+                .Select(x => x.text.Trim())
+                .ToList();
+
+            if (changedSymbols.Count == 0)
+            {
+                Logger.Information("No changes found in Undefined symbols in the Native Wrapper library");
+                return;
+            }
+
+            PrintDiff(diff);
+
+            throw new Exception($"Found differences in undefined symbols ({string.Join(",", changedSymbols)}) in the Native Wrapper library. " +
+                                "Verify that these changes are expected, and will not cause problems. " +
+                                "Removing symbols is generally a safe operation, but adding them could cause crashes. " +
+                                $"If the new symbols are safe to add, update the snapshot file at {verifiedPath} with the " +
+                                "new values");
+        });
+
     Target CompileNativeWrapperNativeTests => _ => _
         .Unlisted()
         .Description("Compile Native wrapper unit tests")

tracer/build/_build/Build.Steps.cs

@@ -99,6 +99,7 @@ partial class Build
     [LazyPathExecutable(name: "cppcheck")] readonly Lazy<Tool> CppCheck;
     [LazyPathExecutable(name: "run-clang-tidy")] readonly Lazy<Tool> RunClangTidy;
     [LazyPathExecutable(name: "patchelf")] readonly Lazy<Tool> PatchElf;
+    [LazyPathExecutable(name: "nm")] readonly Lazy<Tool> Nm;
 
     //OSX Tools
     readonly string[] OsxArchs = { "arm64", "x86_64" };

tracer/build/_build/Build.Utilities.cs

@@ -337,39 +337,7 @@ partial class Build
               var diff = dmp.diff_main(File.ReadAllText(source.ToString().Replace("received", "verified")), File.ReadAllText(source));
               dmp.diff_cleanupSemantic(diff);
 
-              foreach (var t in diff)
-              {
-                  if (t.operation != Operation.EQUAL)
-                  {
-                      var str = DiffToString(t);
-                      if (str.Contains(value: '\n'))
-                      {
-                          // if the diff is multiline, start with a newline so that all changes are aligned
-                          // otherwise it's easy to miss the first line of the diff
-                          str = "\n" + str;
-                      }
-
-                      Logger.Information(str);
-                  }
-              }
-          }
-
-          string DiffToString(Diff diff)
-          {
-              if (diff.operation == Operation.EQUAL)
-              {
-                  return string.Empty;
-              }
-
-              var symbol = diff.operation switch
-              {
-                  Operation.DELETE => '-',
-                  Operation.INSERT => '+',
-                  _ => throw new Exception("Unknown value of the Option enum.")
-              };
-              // put the symbol at the beginning of each line to make diff clearer when whole blocks of text are missing
-              var lines = diff.text.TrimEnd(trimChar: '\n').Split(Environment.NewLine);
-              return string.Join(Environment.NewLine, lines.Select(l => symbol + l));
+              PrintDiff(diff);
           }
       });
 
@@ -511,4 +479,42 @@ private static string GetDefaultRuntimeIdentifier(bool isAlpine)
 
     private static MSBuildTargetPlatform ARM64TargetPlatform = (MSBuildTargetPlatform)"ARM64";
     private static MSBuildTargetPlatform ARM64ECTargetPlatform = (MSBuildTargetPlatform)"ARM64EC";
+
+    private static void PrintDiff(List<Diff> diff, bool printEqual = false)
+    {
+        foreach (var t in diff)
+        {
+            if (printEqual || t.operation != Operation.EQUAL)
+            {
+                var str = DiffToString(t);
+                if (str.Contains(value: '\n'))
+                {
+                    // if the diff is multiline, start with a newline so that all changes are aligned
+                    // otherwise it's easy to miss the first line of the diff
+                    str = "\n" + str;
+                }
+
+                Logger.Information(str);
+            }
+        }
+
+        string DiffToString(Diff diff)
+        {
+            if (diff.operation == Operation.EQUAL)
+            {
+                return string.Empty;
+            }
+
+            var symbol = diff.operation switch
+            {
+                Operation.DELETE => '-',
+                Operation.INSERT => '+',
+                _ => throw new Exception("Unknown value of the Option enum.")
+            };
+            // put the symbol at the beginning of each line to make diff clearer when whole blocks of text are missing
+            var lines = diff.text.TrimEnd(trimChar: '\n').Split(Environment.NewLine);
+            return string.Join(Environment.NewLine, lines.Select(l => symbol + l));
+        }
+
+    }
 }

tracer/build/_build/Build.cs

@@ -230,6 +230,7 @@ void DeleteReparsePoints(string path)
         .Description("")
         .After(Clean)
         .DependsOn(CompileNativeWrapper)
+        .DependsOn(TestNativeWrapper)
         .DependsOn(PublishNativeWrapper);
 
     Target PackageTracerHome => _ => _

tracer/test/snapshots/native-wrapper-symbols-arm64.verified.txt

@@ -0,0 +1,14 @@
+__errno_location
+access
+asprintf
+free
+getauxval
+getenv
+malloc
+strcasecmp
+strcmp
+strcpy
+strlen
+strncmp
+strncpy
+strrchr

tracer/test/snapshots/native-wrapper-symbols-x64.verified.txt

@@ -0,0 +1,14 @@
+__errno_location
+__tls_get_addr
+access
+asprintf
+free
+getenv
+malloc
+strcasecmp
+strcmp
+strcpy
+strlen
+strncmp
+strncpy
+strrchr