[lldb] Properly cache the result of MachProcess::GetPlatform

[talkeren]

If MachProcess::GetProcessPlatformViaDYLDSPI fails and return 0, we don't
want to call it everytime as it won't change the result. So use
std::optional to cache wether we already calculated the value.

Alleviate the impact of issue #140610

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[llvmbot]

@llvm/pr-subscribers-lldb

Author: Tal Keren (talkeren)

Changes

If MachProcess::GetProcessPlatformViaDYLDSPI fails and return 0, we don't
want to call it everytime as it won't change the result. So use
std::optional to cache wether we already calculated the value.

---

Full diff: https://github.com/llvm/llvm-project/pull/140611.diff

2 Files Affected:

• (modified) lldb/tools/debugserver/source/MacOSX/MachProcess.h (+1-1)
• (modified) lldb/tools/debugserver/source/MacOSX/MachProcess.mm (+7-5)

diff --git a/lldb/tools/debugserver/source/MacOSX/MachProcess.h b/lldb/tools/debugserver/source/MacOSX/MachProcess.h
index 56bc9d6c7461e..516a77c0bd6c8 100644
--- a/lldb/tools/debugserver/source/MacOSX/MachProcess.h
+++ b/lldb/tools/debugserver/source/MacOSX/MachProcess.h
@@ -398,7 +398,7 @@ class MachProcess {
 
   pid_t m_pid;           // Process ID of child process
   cpu_type_t m_cpu_type; // The CPU type of this process
-  uint32_t m_platform;   // The platform of this process
+  std::optional<uint32_t> m_platform;   // The platform of this process
   int m_child_stdin;
   int m_child_stdout;
   int m_child_stderr;
diff --git a/lldb/tools/debugserver/source/MacOSX/MachProcess.mm b/lldb/tools/debugserver/source/MacOSX/MachProcess.mm
index 3afaaa2f64c00..ce74dd1cadfb0 100644
--- a/lldb/tools/debugserver/source/MacOSX/MachProcess.mm
+++ b/lldb/tools/debugserver/source/MacOSX/MachProcess.mm
@@ -1039,9 +1039,9 @@ static bool mach_header_validity_test(uint32_t magic, uint32_t cputype) {
 };
 
 uint32_t MachProcess::GetPlatform() {
-  if (m_platform == 0)
+  if (!m_platform)
     m_platform = MachProcess::GetProcessPlatformViaDYLDSPI();
-  return m_platform;
+  return *m_platform;
 }
 
 uint32_t MachProcess::GetProcessPlatformViaDYLDSPI() {
@@ -1058,7 +1058,9 @@ static bool mach_header_validity_test(uint32_t magic, uint32_t cputype) {
   }
   return platform;
 }
-
+If `MachProcess::GetProcessPlatformViaDYLDSPI` fails and return 0, we don't
+want to call it everytime as it won't change the result. So use
+std::optional to cache wether we already calculated the value.
 void MachProcess::GetAllLoadedBinariesViaDYLDSPI(
     std::vector<struct binary_image_information> &image_infos) {
   kern_return_t kern_ret;
@@ -1323,7 +1325,7 @@ static bool mach_header_validity_test(uint32_t magic, uint32_t cputype) {
   // Clear any cached thread list while the pid and task are still valid
 
   m_task.Clear();
-  m_platform = 0;
+  m_platform.reset();
   // Now clear out all member variables
   m_pid = INVALID_NUB_PROCESS;
   if (!detaching)
@@ -1754,7 +1756,7 @@ static uint64_t bits(uint64_t value, uint32_t msbit, uint32_t lsbit) {
 
   // NULL our task out as we have already restored all exception ports
   m_task.Clear();
-  m_platform = 0;
+  m_platform.reset();
 
   // Clear out any notion of the process we once were
   const bool detaching = true;

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[JDevlieghere]

LGTM, but I'd like @jasonmolenda to sign off as the debugserver maintainer.

[talkeren]

Closing it following the discussion in the issue - I made a new PR that fixes it differently without change the current behaviour.