[ObjectFileMachO] Disable memory caching for savecore.

[davide]

Summary

It's not really useful, and largely increases the footprint.

rdar://problem/49293525

[davide]

try

[jasonmolenda]

Looks good. Removing that printf is good. Could you also remove the printf("mach_header:...") in the same function?

It would be nice if include/lldb/Target/Process.h had the decl for ReadMemoryFromInferior right after ReadMemory(), and a comment that ReadMemoryFromInferior does not go through the memory cache (and most callers should go through ReadMemory()) so people know what the difference is.

[davide]

In D59896#1445310, @jasonmolenda wrote:

Looks good. Removing that printf is good. Could you also remove the printf("mach_header:...") in the same function?

It would be nice if include/lldb/Target/Process.h had the decl for ReadMemoryFromInferior right after ReadMemory(), and a comment that ReadMemoryFromInferior does not go through the memory cache (and most callers should go through ReadMemory()) so people know what the difference is.

I'll do that as a follow-up. Thank you Jason!

[davide]

Done.

$ git llvm push
Pushing 3 commits:
  d3e193e68a7 [ObjectFileMachO] Disable memory caching for savecore.
  10502683510 [ObjectFileMachO] Remove another debugging aid.
  a619d7b69b9 [Process] Reorder declarations and document ReadMemoryFromInferior.
Sending        lldb/trunk/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
Transmitting file data .done
Committing transaction...
Committed revision 357134.
Committed d3e193e68a7 to svn.
Sending        lldb/trunk/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
Transmitting file data .done
Committing transaction...
Committed revision 357135.
Committed 10502683510 to svn.
Sending        lldb/trunk/include/lldb/Target/Process.h
Transmitting file data .done
Committing transaction...
Committed revision 357136.
Committed a619d7b69b9 to svn.

lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp

if (target_triple.getVendor() == llvm::Triple::Apple &&
             uint32_t prot = 0;
             if (range_info.GetReadable() == MemoryRegionInfo::eYes)
               prot |= VM_PROT_READ;
             if (range_info.GetWritable() == MemoryRegionInfo::eYes)
               prot |= VM_PROT_WRITE;
             if (range_info.GetExecutable() == MemoryRegionInfo::eYes)
               prot |= VM_PROT_EXECUTE;
 
-            //                        printf ("[%3u] [0x%16.16" PRIx64 " -
-            //                        0x%16.16" PRIx64 ") %c%c%c\n",
-            //                                range_info_idx,
-            //                                addr,
-            //                                size,
-            //                                (prot & VM_PROT_READ   ) ? 'r' :
-            //                                '-',
-            //                                (prot & VM_PROT_WRITE  ) ? 'w' :
-            //                                '-',
-            //                                (prot & VM_PROT_EXECUTE) ? 'x' :
-            //                                '-');
-
             if (prot != 0) {
               uint32_t cmd_type = LC_SEGMENT_64;
               uint32_t segment_size = sizeof(segment_command_64);
               if (addr_byte_size == 4) {
                 cmd_type = LC_SEGMENT;
                 segment_size = sizeof(segment_command);
               }
               segment_command_64 segment = {
if (target_triple.getVendor() == llvm::Triple::Apple &&
                        " bytes of data for memory region at 0x%" PRIx64 "\n",
                        segment.vmsize, segment.vmaddr);
                 addr_t bytes_left = segment.vmsize;
                 addr_t addr = segment.vmaddr;
                 Status memory_read_error;
                 while (bytes_left > 0 && error.Success()) {
                   const size_t bytes_to_read =
                       bytes_left > sizeof(bytes) ? sizeof(bytes) : bytes_left;
-                  const size_t bytes_read = process_sp->ReadMemory(
+
+                  // In a savecore setting, we don't really care about caching,
+                  // as the data is dumped and very likely never read again,
+                  // so we call ReadMemoryFromInferior to bypass it.
+                  const size_t bytes_read = process_sp->ReadMemoryFromInferior(
                       addr, bytes, bytes_to_read, memory_read_error);
+
                   if (bytes_read == bytes_to_read) {
                     size_t bytes_written = bytes_read;
                     error = core_file.Write(bytes, bytes_written);
                     bytes_left -= bytes_read;
                     addr += bytes_read;
                   } else {
                     // Some pages within regions are not readable, those should
                     // be zero filled