[llvm] 75b5541 - [llvm-exegesis] Switch to using PTRACE_ATTACH instead of PTRACE_SEIZE

[Aiden Grossman via llvm-commits]

Author: Aiden Grossman
Date: 2023-07-06T19:40:19-07:00
New Revision: 75b5541fe5d096d115d213cb8dc8a10cf3d11fbd

URL: https://github.com/llvm/llvm-project/commit/75b5541fe5d096d115d213cb8dc8a10cf3d11fbd
DIFF: https://github.com/llvm/llvm-project/commit/75b5541fe5d096d115d213cb8dc8a10cf3d11fbd.diff

LOG: [llvm-exegesis] Switch to using PTRACE_ATTACH instead of PTRACE_SEIZE

This patch switches from using PTRACE_SEIZE within the subprocess
benchmark runner for llvm-exegesis as PTRACE_SEIZE was introduced in
Linux kernel 3.4. Some LLVM users were reporting build failures as they
are using Kernel versions older than 3.4 (such as on CentOS/RHEL 6),
hence the patch.

Added: 
    

Modified: 
    llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp b/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
index 6d0b754a7c899c..ba91f5d89fea07 100644
--- a/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
+++ b/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
@@ -7,6 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include <array>
+#include <cerrno>
+#include <iostream>
 #include <memory>
 #include <string>
 
@@ -249,10 +251,21 @@ class SubProcessFunctionExecutorImpl
                                  "to child process failed: " +
                                  Twine(strerror(errno)));
 
-    if (ptrace(PTRACE_SEIZE, ParentOrChildPID, NULL, NULL) != 0)
-      return make_error<Failure>("Failed to seize the child process: " +
+    if (ptrace(PTRACE_ATTACH, ParentOrChildPID, NULL, NULL) != 0)
+      return make_error<Failure>("Failed to attach to the child process: " +
                                  Twine(strerror(errno)));
 
+    if (wait(NULL) == -1) {
+      return make_error<Failure>(
+          "Failed to wait for child process to stop after attaching: " +
+          Twine(strerror(errno)));
+    }
+
+    if (ptrace(PTRACE_CONT, ParentOrChildPID, NULL, NULL) != 0)
+      return make_error<Failure>(
+          "Failed to continue execution of the child process: " +
+          Twine(strerror(errno)));
+
     int ChildStatus;
     if (wait(&ChildStatus) == -1) {
       return make_error<Failure>(