[Bug 18648] New: Section's m_file_addr left unset after Mach-O parsing

Bug ID 18648
Summary Section’s m_file_addr left unset after Mach-O parsing
Product lldb
Version unspecified
Hardware All
Status NEW
Severity normal
Priority P
Component All Bugs
Assignee lldb-dev@cs.uiuc.edu
Reporter josharian@gmail.com
Classification Unclassified

Created attachment 11965 [details]
Compiled executable (simple.go)

I found this while digging into golang.org/issue/7070.


(1) Compile [http://play.golang.org/p/i_6zF3EoLG](http://play.golang.org/p/i_6zF3EoLG) using Go 1.2. I have attached a
compiled version for reference, called just simple.
(2) lldb simple
(3) breakpoint set -a 0x2000
(4) run


Assertion failed: (sizeof(arangeDescriptor.address) >= m_header.addr_size),
function Extract, file
line 208.


In the executable attached, __debug_aranges is at offset 514379. The data being
parsed to construct m_header in DWARFDebugArangeSet::Extract, however, is at
offset 360448, which is the beginning of the DWARF segment, not the
__debug_aranges section. This junk data causes the assertion failure.

The aranges data is prepared in SymbolFileDWARF::GetCachedSectionData, at
SymbolFileDWARF.cpp:716. The data offset calculation uses
section_sp->GetOffset(), which should be the offset of the __debug_aranges
section relative to the containing DWARF segment. That is, it should return
153931. In this case, however, it returns 0.

This is because Section::GetOffset returns m_file_addr, which is documented to
be the file offset relative to the parent. However, m_file_addr never gets set
in ObjectFileMachO::CreateSections (or anywhere else). There is one call to
Section::SetFileAddress, at line 1124, but it does not get hit during parsing
of the attached executable.

The following patch fixes the problem by using m_file_offset in
Section::GetOffset. I suspect, however, that the correct fix is to populate
m_file_addr during Mach-O parsing.

diff --git a/source/Core/Section.cpp b/source/Core/Section.cpp
index 28d7d93..f6f6fe2 100644
--- a/source/Core/Section.cpp
+++ b/source/Core/Section.cpp
@@ -123,7 +123,7 @@ Section::GetOffset () const
     // This section has a parent which means m_file_addr is an offset.
     SectionSP parent_sp (GetParent ());
     if (parent_sp)
-        return m_file_addr;
+        return m_file_offset - parent_sp->m_file_offset;

     // This section has no parent, so there is no offset to be had
     return 0;

Greg Clayton changed bug 18648

What Removed Added
CC clayborg@gmail.com
Resolution INVALID

Comment # 1 on bug 18648 from Greg Clayton

This is actually due to the mach-o file being not properly formed. Looking at
the segments and sections:

% dwarfdump -R simple