[Lldb-commits] [PATCH] D101390: Change Target::ReadMemory to ensure the amount of memory read from the file-cache is the amount requested.

[Augusto Noronha via Phabricator via lldb-commits]

augusto2112 updated this revision to Diff 341550.
augusto2112 marked an inline comment as done.
augusto2112 added a comment.

Rely on `unique_ptr`'s bool operator, instead of checking the underlying pointer.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D101390/new/

https://reviews.llvm.org/D101390

Files:
  lldb/source/Target/Target.cpp


Index: lldb/source/Target/Target.cpp
===================================================================
--- lldb/source/Target/Target.cpp
+++ lldb/source/Target/Target.cpp
@@ -1753,19 +1753,30 @@
   if (!resolved_addr.IsValid())
     resolved_addr = addr;
 
-  bool is_readonly = false;
+  // If we read from the file cache but can't get as many bytes as requested,
+  // we keep the result around in this buffer, in case this result is the
+  // best we can do.
+  std::unique_ptr<uint8_t[]> file_cache_read_buffer;
+  size_t file_cache_bytes_read = 0;
+
   // Read from file cache if read-only section.
   if (!force_live_memory && resolved_addr.IsSectionOffset()) {
     SectionSP section_sp(resolved_addr.GetSection());
     if (section_sp) {
       auto permissions = Flags(section_sp->GetPermissions());
-      is_readonly = !permissions.Test(ePermissionsWritable) &&
-                    permissions.Test(ePermissionsReadable);
-    }
-    if (is_readonly) {
-      bytes_read = ReadMemoryFromFileCache(resolved_addr, dst, dst_len, error);
-      if (bytes_read > 0)
-        return bytes_read;
+      bool is_readonly = !permissions.Test(ePermissionsWritable) &&
+                         permissions.Test(ePermissionsReadable);
+      if (is_readonly) {
+        file_cache_bytes_read =
+            ReadMemoryFromFileCache(resolved_addr, dst, dst_len, error);
+        if (file_cache_bytes_read == dst_len)
+          return file_cache_bytes_read;
+        else if (file_cache_bytes_read > 0) {
+          file_cache_read_buffer =
+              std::make_unique<uint8_t[]>(file_cache_bytes_read);
+          std::memcpy(file_cache_read_buffer.get(), dst, file_cache_bytes_read);
+        }
+      }
     }
   }
 
@@ -1804,7 +1815,14 @@
     }
   }
 
-  if (!is_readonly && resolved_addr.IsSectionOffset()) {
+  if (file_cache_read_buffer && file_cache_bytes_read > 0) {
+    // Reading from the process failed. If we've previously succeeded in reading
+    // something from the file cache, then copy that over and return that.
+    std::memcpy(dst, file_cache_read_buffer.get(), file_cache_bytes_read);
+    return file_cache_bytes_read;
+  }
+
+  if (!file_cache_read_buffer && resolved_addr.IsSectionOffset()) {
     // If we didn't already try and read from the object file cache, then try
     // it after failing to read from the process.
     return ReadMemoryFromFileCache(resolved_addr, dst, dst_len, error);


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