docs: Sync with upstream

Author: danobi

docs/master.html

@@ -1676,10 +1676,10 @@ <h2 id="_builtins">Builtins</h2>
 </tr>
 <tr>
 <td class="tableblock halign-left valign-top"><p class="tableblock">retval</p></td>
-<td class="tableblock halign-left valign-top"><p class="tableblock">int64</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">uint64</p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock">n/a</p></td>
 <td class="tableblock halign-left valign-top"><p class="tableblock">n/a</p></td>
-<td class="tableblock halign-left valign-top"><p class="tableblock">Value returned by the function being traced (kretprobe, uretprobe, fexit)</p></td>
+<td class="tableblock halign-left valign-top"><p class="tableblock">Value returned by the function being traced (kretprobe, uretprobe, fexit). For kretprobe and uretprobe, its type is <code>uint64</code>, but for fexit it depends. You can look up the type using <code>bpftrace -lv</code></p></td>
 </tr>
 <tr>
 <td class="tableblock halign-left valign-top"><p class="tableblock">tid</p></td>

src/docs/master.adoc

@@ -1192,10 +1192,10 @@ For string arguments use the `str()` call to retrieve the value.
 | The return keyword is used to exit the current probe. This differs from exit() in that it doesn't exit bpftrace.
 
 | retval
-| int64
+| uint64
 | n/a
 | n/a
-| Value returned by the function being traced (kretprobe, uretprobe, fexit)
+| Value returned by the function being traced (kretprobe, uretprobe, fexit). For kretprobe and uretprobe, its type is `uint64`, but for fexit it depends. You can look up the type using `bpftrace -lv`
 
 | tid
 | uint32