[Lldb-commits] [lldb] 1d83f82 - [lldb][Darwin] Don't add zero-length segments to SectionLoadList (#195206)

[via lldb-commits]

Author: Jason Molenda
Date: 2026-04-30T22:43:12-07:00
New Revision: 1d83f8218b5c9dbe00309280d265252e852abb03

URL: https://github.com/llvm/llvm-project/commit/1d83f8218b5c9dbe00309280d265252e852abb03
DIFF: https://github.com/llvm/llvm-project/commit/1d83f8218b5c9dbe00309280d265252e852abb03.diff

LOG: [lldb][Darwin] Don't add zero-length segments to SectionLoadList (#195206)

On Darwin systems with a shared cache, all the system binaries are
combined into a single range of virtual address space, placing all the
TEXT segments together, all the DATA segments together, etc. It shrinks
the sizes of the segments from their on-disk file size to the actual
size needed for their contents, instead of observing page alignment
rules for segments.

And in one uncommon case, it is possible for a segment to not be put in
the shared cache virtual range at all.

When DynamicLoaderDarwin adds each file's segments to the Target
SectionLoadList (the table showing what VM ranges they are mapped to),
we're using the original file's segment sizes. But the in-memory segment
sizes may be different for binaries in the shared cache. And for a
segment which is eliminated entirely (zero length), we'll get warnings
as the next segment is added to the same address in the SectionLoadList.

To start with, this PR is handling the special case of these segments
that become zero length -- by not adding them to the SectionLoadList at
all.

rdar://174948380

Added: 
    

Modified: 
    lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.cpp

Removed: 
    


################################################################################
diff  --git a/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.cpp b/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.cpp
index afa0ef28a381d..894ee16935e7e 100644
--- a/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.cpp
+++ b/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.cpp
@@ -275,6 +275,7 @@ void DynamicLoaderDarwin::UnloadAllImages() {
 bool DynamicLoaderDarwin::UpdateImageLoadAddress(Module *module,
                                                  ImageInfo &info) {
   bool changed = false;
+  Log *log = GetLog(LLDBLog::DynamicLoader);
   if (module) {
     ObjectFile *image_object_file = module->GetObjectFile();
     if (image_object_file) {
@@ -305,6 +306,23 @@ bool DynamicLoaderDarwin::UpdateImageLoadAddress(Module *module,
               const bool warn_multiple =
                   section_sp->GetName() != g_section_name_LINKEDIT;
 
+              // If a segment was eliminated for the in-memory image,
+              // don't map it into lldb's target section load list.
+              if (info.segments[i].vmsize == 0) {
+                LLDB_LOGF(log, "%s: Omitting zero-size segment %s",
+                          info.file_spec.GetFilename().AsCString(""),
+                          info.segments[i].name.AsCString(""));
+                continue;
+              }
+
+              if (info.segments[i].vmsize != section_sp->GetByteSize())
+                LLDB_LOGF(log,
+                          "%s: In-memory segment size for %s is %" PRIx64
+                          " but file segment size is %" PRIx64,
+                          info.file_spec.GetFilename().AsCString(""),
+                          info.segments[i].name.AsCString(""),
+                          info.segments[i].vmsize, section_sp->GetByteSize());
+
               changed = m_process->GetTarget().SetSectionLoadAddress(
                   section_sp, new_section_load_addr, warn_multiple);
             }