dtrace: fix on macOS (except in the package)

The package needs https://github.com/NixOS/nixpkgs/pull/392918

CC: https://git.lix.systems/lix-project/lix/issues/757
Change-Id: Id040a83d845f98fa1093b782cce2a015b5c85d9f

lix/libstore/filetransfer.cc

@@ -9,11 +9,15 @@
 #include "lix/libutil/strings.hh"
 #include "lix/libutil/thread-name.hh"
 #include "lix/libutil/tracepoint.hh"
-#include <cstddef>
 
+#include <cstddef>
 #include <cstdio>
 #include <kj/encoding.h>
 
+#if ENABLE_DTRACE
+#include "trace-probes.gen.hh"
+#endif
+
 #if ENABLE_S3
 #include <aws/core/client/ClientConfiguration.h>
 #endif
@@ -948,7 +952,7 @@ struct curlFileTransfer : public FileTransfer
 
         size_t read(char * data, size_t len) override
         {
-            TRACE(DTRACE_PROBE2(lix_store, filetransfer__read, uri.c_str(), len));
+            TRACE(LIX_STORE_FILETRANSFER_READ(uri.c_str(), len));
 
             size_t total = 0;
             while (total < len && awaitData()) {

lix/libstore/trace-probes.d

@@ -1,9 +1,13 @@
 // I don't know how the rest of these stability attrs work and tbh I don't care
 // either; these probes are not stable API and we don't need to be more
 // specific about exactly how.
-#pragma D attributes Unstable/Unstable/Common provider lix_store provider
 
 provider lix_store {
     /** See filetransfer.cc; this is the consumption side, not the curl/production side. */
-    probe filetransfer__read(string url, size_t length);
+    probe filetransfer__read(const char * url, size_t length);
 };
+#pragma D attributes Unstable/Unstable/Common provider lix_store provider
+#pragma D attributes Unstable/Unstable/Common provider lix_store module
+#pragma D attributes Unstable/Unstable/Common provider lix_store function
+#pragma D attributes Unstable/Unstable/Common provider lix_store name
+#pragma D attributes Unstable/Unstable/Common provider lix_store args

lix/libutil/tracepoint.hh

@@ -15,10 +15,13 @@
 
 #include "lix/config.h"
 
-// NOTE: glib disables this for the clang static analyzer, idk if we need to also
-#if HAVE_DTRACE
+// The clang static analyzer is busted on these and throws reserved-identifier
+// lints at the crimes they put in the headers. Oh well.
+#if HAVE_DTRACE && !defined(__clang_analyzer__)
+#define ENABLE_DTRACE 1
 #define TRACE(body) body
 #include <sys/sdt.h>
 #else
+#define ENABLE_DTRACE 0
 #define TRACE(body)
 #endif

meson.build

@@ -417,11 +417,29 @@ if dtrace_feature.enabled()
   # NOTE: glib seems to have had to hack some stuff up that we are not hacking
   # up. I don't know why.
   # https://github.com/GNOME/glib/blob/03f7c1fbf3a3784cb4c3604f83ca3645e9225577/meson.build#L2420-L2434
-  dtrace_object_gen = generator(dtrace_exe,
-    output : '@BASENAME@.o',
-    arguments : ['-G', '-s', '@INPUT@', '-o', '@OUTPUT@'])
+
+  # Darwin doesn't require an object generator for dtrace, but it's preferable
+  # to still have the build structured the same, so we generate empty object
+  # files with clang.
+  if is_darwin
+    dtrace_object_gen = generator(bash,
+      output : '@BASENAME@.o',
+      arguments : [
+        '-c',
+        'exec "$@"',
+        '--',
+        cxx.cmd_array(),
+        '-xc++',
+        '-c', '/dev/null',
+        '-o', '@OUTPUT@'
+      ])
+  else
+    dtrace_object_gen = generator(dtrace_exe,
+      output : '@BASENAME@.o',
+      arguments : ['-G', '-s', '@INPUT@', '-o', '@OUTPUT@'])
+  endif
   dtrace_header_gen = generator(dtrace_exe,
-    output : '@BASENAME@.gen.h',
+    output : '@BASENAME@.gen.hh',
     arguments : ['-h', '-s', '@INPUT@', '-o', '@OUTPUT@'])
 endif
 configdata += {