jasonmolenda created this revision.
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When lldb is processing the first couple of binaries in a process launch, it
needs to compute load addresses before the files' sections have been added to
the TargetSectionList, so our normal mechanism is not sufficient.
ObjectFileMachO::ParseSymtab() calls GetMachHeaderSection() to find that
segment, then uses the difference between that segment and the LINKEDIT
segment, plus the Mach-O header load address that we were given, to calculate
the load address of LINKEDIT.
This scheme works until one of the binaries we're treating in this special way
is in the shared cache. GetMachHeaderSection() explicitly looks for a segment
at file offset 0, as a way of implying the __TEXT segment without hardcoding
its name. In a file in the shared cache, it will have a non-zero file address.
It's laudable that ParseSymtab already handles the offset calculation
correctly for a non-zero file offset -- but it won't match a segment which is
nonzero.
This patch adds a backup mechanism if we find no segment at file offset 0, to
find the __TEXT segment and return that.
Outside of an environment where one of these very initial binaries are in the
shared cache, this can't be reproduced. Individual Mach-O binaries have file
__TEXT with a file offset of 0. I haven't thought of a way to construct a well
formed Mach-O binary that behaves like this, outside of the shared cache binary
blob.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D119602
Files:
lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
Index: lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
===================================================================
--- lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
+++ lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
@@ -6100,6 +6100,15 @@
if (section->GetFileOffset() == 0 && SectionIsLoadable(section))
return section;
}
+
+ // We may have a binary with in the shared cache that has a non-zero
+ // file address for its first segment, traditionally the __TEXT segment.
+ // Search for it by name and return it as our next best guess.
+ SectionSP text_segment_sp =
+ GetSectionList()->FindSectionByName(GetSegmentNameTEXT());
+ if (text_segment_sp.get() && SectionIsLoadable(text_segment_sp.get()))
+ return text_segment_sp.get();
+
return nullptr;
}
Index: lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
===================================================================
--- lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
+++ lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
@@ -6100,6 +6100,15 @@
if (section->GetFileOffset() == 0 && SectionIsLoadable(section))
return section;
}
+
+ // We may have a binary with in the shared cache that has a non-zero
+ // file address for its first segment, traditionally the __TEXT segment.
+ // Search for it by name and return it as our next best guess.
+ SectionSP text_segment_sp =
+ GetSectionList()->FindSectionByName(GetSegmentNameTEXT());
+ if (text_segment_sp.get() && SectionIsLoadable(text_segment_sp.get()))
+ return text_segment_sp.get();
+
return nullptr;
}
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