perf(profiling): remove utf8 check (#13054)

This will remove ~160ms per minute from stack v2 cpu time as measured on
a test environment. The strings passed from echion are already validated
to utf-8, via
https://github.com/taegyunkim/echion/blob/taegyunkim/unwind-task-fix/echion/strings.h#L48
and we don't seem to be deleting any items in the string table, from
which the strings are coming from. So I don't think there's any more
need for validation. Also, libdatadog does utf8 validation too.

![Screenshot 2025-04-17 at 4 32
34 PM](https://github.com/user-attachments/assets/2354d19e-efde-4a4a-aa3e-18aff407d74e)


## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
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implications of this PR as reported in the benchmarks PR comment
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[release branch maintenance
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Author: taegyunkim

ddtrace/internal/datadog/profiling/stack_v2/CMakeLists.txt

@@ -65,7 +65,6 @@ add_cppcheck_target(
     ${CMAKE_CURRENT_SOURCE_DIR}
     INCLUDE
     ${CMAKE_CURRENT_SOURCE_DIR}/include
-    ${CMAKE_CURRENT_SOURCE_DIR}/include/vendored
     ${CMAKE_CURRENT_SOURCE_DIR}/include/util
     ${CMAKE_CURRENT_SOURCE_DIR}/..
     ${echion_SOURCE_DIR}

ddtrace/internal/datadog/profiling/stack_v2/include/vendored/utf8_validate.hpp

@@ -1,7 +1,6 @@
 #include "stack_renderer.hpp"
 
 #include "thread_span_links.hpp"
-#include "utf8_validate.hpp"
 
 #include "echion/strings.h"
 
@@ -144,17 +143,6 @@ StackRenderer::render_frame(Frame& frame)
 
     auto line = frame.location.line;
 
-    // Normally, further utf-8 validation would be pointless here, but we may be reading data where the
-    // string pointer was valid, but the string is actually garbage data at the exact time of the read.
-    // This is rare, but blowing some cycles on early validation allows the sample to be retained by
-    // libdatadog, so we can evaluate the actual impact of this scenario in live scenarios.
-    static const std::string_view invalid = "<invalid_utf8>";
-    if (!utf8_check_is_valid(name_str.data(), name_str.size())) {
-        name_str = invalid;
-    }
-    if (!utf8_check_is_valid(filename_str.data(), filename_str.size())) {
-        filename_str = invalid;
-    }
     // DEV: Echion pushes a dummy frame containing task name, and its line
     // number is set to 0.
     if (!pushed_task_name and line == 0) {

ddtrace/internal/datadog/profiling/stack_v2/src/stack_renderer.cpp

@@ -0,0 +1,7 @@
+---
+#instructions:
+fixes:
+  - |
+    profiling: reduces overhead of the v2 stack sampler by removing unnecessary
+    and expensive utf-8 validation
+