Open ELF core dumps with more than 64K sections
Summary:
Problem:
There are three filelds in the ELF header - e_phnum, e_shnum, and e_shstrndx -
that could be bigger than 64K and therefore do not fit in 16 bits reserved for
them in the header. If this happens, pretty often there is a special section at
index 0 which contains their real values for these fields in the section header
in the fields sh_info, sh_size, and sh_link respectively.
Fix:
- Rename original fields in the header declaration. We want to have them around
just in case.
- Reintroduce these fields as 32-bit members at the end of the header. By default
they are initialized from the header in Parse() method.
- In Parse(), detect the situation when the header might have been extended into
section info #0 and try to read it from the same data source.
- ObjectFileELF::GetModuleSpecifications accesses some of these fields but the
original parse uses too small data source. Re-parse the header if necessary
using bigger data source.
- ProcessElfCore::CreateInstance uses header with potentially sentinel values,
but it does not access these fields, so a comment here is enough.
Reviewers: labath
Reviewed By: labath
Subscribers: davidb, lldb-commits, mgorny
Differential Revision: https://reviews.llvm.org/D29095
Author: Eugene Birukov <eugenebi@hotmail.com>
llvm-svn: 293714
diff --git a/lldb/source/Plugins/ObjectFile/ELF/ELFHeader.cpp b/lldb/source/Plugins/ObjectFile/ELF/ELFHeader.cpp
index a3e8239..34b32a1 100644
--- a/lldb/source/Plugins/ObjectFile/ELF/ELFHeader.cpp
+++ b/lldb/source/Plugins/ObjectFile/ELF/ELFHeader.cpp
@@ -81,6 +81,39 @@
return eByteOrderInvalid;
}
+bool ELFHeader::HasHeaderExtension() const {
+ bool result = false;
+
+ // Check if any of these values looks like sentinel.
+ result |= e_phnum_hdr == 0xFFFF; // PN_XNUM
+ result |= e_shnum_hdr == SHN_UNDEF;
+ result |= e_shstrndx_hdr == SHN_XINDEX;
+
+ // If header extension is present, the section offset cannot be null.
+ result &= e_shoff != 0;
+
+ // Done.
+ return result;
+}
+
+void ELFHeader::ParseHeaderExtension(lldb_private::DataExtractor &data) {
+ // Extract section #0 header.
+ ELFSectionHeader section_zero;
+ lldb::offset_t offset = 0;
+ lldb_private::DataExtractor sh_data(data, e_shoff, e_shentsize);
+ bool ok = section_zero.Parse(sh_data, &offset);
+
+ // If we succeeded, fix the header.
+ if (ok) {
+ if (e_phnum_hdr == 0xFFFF) // PN_XNUM
+ e_phnum = section_zero.sh_info;
+ if (e_shnum_hdr == SHN_UNDEF)
+ e_shnum = section_zero.sh_size;
+ if (e_shstrndx_hdr == SHN_XINDEX)
+ e_shstrndx = section_zero.sh_link;
+ }
+}
+
bool ELFHeader::Parse(lldb_private::DataExtractor &data,
lldb::offset_t *offset) {
// Read e_ident. This provides byte order and address size info.
@@ -112,6 +145,16 @@
if (data.GetU16(offset, &e_ehsize, 6) == NULL)
return false;
+ // Initialize e_phnum, e_shnum, and e_shstrndx with the values
+ // read from the header.
+ e_phnum = e_phnum_hdr;
+ e_shnum = e_shnum_hdr;
+ e_shstrndx = e_shstrndx_hdr;
+
+ // See if we have extended header in section #0.
+ if (HasHeaderExtension())
+ ParseHeaderExtension(data);
+
return true;
}
diff --git a/lldb/source/Plugins/ObjectFile/ELF/ELFHeader.h b/lldb/source/Plugins/ObjectFile/ELF/ELFHeader.h
index 71b200f..e6738a1 100644
--- a/lldb/source/Plugins/ObjectFile/ELF/ELFHeader.h
+++ b/lldb/source/Plugins/ObjectFile/ELF/ELFHeader.h
@@ -24,6 +24,7 @@
#include "llvm/Support/ELF.h"
#include "lldb/lldb-enumerations.h"
+#include "lldb/lldb-types.h"
namespace lldb_private {
class DataExtractor;
@@ -65,10 +66,17 @@
elf_half e_machine; ///< Target architecture.
elf_half e_ehsize; ///< Byte size of the ELF header.
elf_half e_phentsize; ///< Size of a program header table entry.
- elf_half e_phnum; ///< Number of program header entries.
+ elf_half e_phnum_hdr; ///< Number of program header entries.
elf_half e_shentsize; ///< Size of a section header table entry.
- elf_half e_shnum; ///< Number of section header entries.
- elf_half e_shstrndx; ///< String table section index.
+ elf_half e_shnum_hdr; ///< Number of section header entries.
+ elf_half e_shstrndx_hdr; ///< String table section index.
+
+ // In some cases these numbers do not fit in 16 bits and they are
+ // stored outside of the header in section #0. Here are the actual
+ // values.
+ elf_word e_phnum; ///< Number of program header entries.
+ elf_word e_shnum; ///< Number of section header entries.
+ elf_word e_shstrndx; ///< String table section index.
ELFHeader();
@@ -102,6 +110,14 @@
unsigned GetRelocationJumpSlotType() const;
//--------------------------------------------------------------------------
+ /// Check if there should be header extension in section header #0
+ ///
+ /// @return
+ /// True if parsing the ELFHeader requires reading header extension
+ /// and false otherwise.
+ bool HasHeaderExtension() const;
+
+ //--------------------------------------------------------------------------
/// Parse an ELFHeader entry starting at position \p offset and
/// update the data extractor with the address size and byte order
/// attributes as defined by the header.
@@ -137,6 +153,16 @@
/// The number of bytes forming an address in the ELF file (either 4 or
/// 8), else zero if the address size could not be determined.
static unsigned AddressSizeInBytes(const uint8_t *magic);
+
+private:
+
+ //--------------------------------------------------------------------------
+ /// Parse an ELFHeader header extension entry. This method is called
+ /// by Parse().
+ ///
+ /// @param[in] data
+ /// The DataExtractor to read from.
+ void ParseHeaderExtension(lldb_private::DataExtractor &data);
};
//------------------------------------------------------------------------------
diff --git a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
index fa79b24..44ea01d 100644
--- a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
+++ b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
@@ -610,7 +610,8 @@
DataExtractor data;
data.SetData(data_sp);
elf::ELFHeader header;
- if (header.Parse(data, &data_offset)) {
+ lldb::offset_t header_offset = data_offset;
+ if (header.Parse(data, &header_offset)) {
if (data_sp) {
ModuleSpec spec(file);
@@ -645,10 +646,24 @@
__FUNCTION__, file.GetPath().c_str());
}
+ // In case there is header extension in the section #0, the header
+ // we parsed above could have sentinel values for e_phnum, e_shnum,
+ // and e_shstrndx. In this case we need to reparse the header
+ // with a bigger data source to get the actual values.
+ size_t section_header_end = header.e_shoff + header.e_shentsize;
+ if (header.HasHeaderExtension() &&
+ section_header_end > data_sp->GetByteSize()) {
+ data_sp = file.MemoryMapFileContentsIfLocal (file_offset,
+ section_header_end);
+ data.SetData(data_sp);
+ lldb::offset_t header_offset = data_offset;
+ header.Parse(data, &header_offset);
+ }
+
// Try to get the UUID from the section list. Usually that's at the
// end, so
// map the file in if we don't have it already.
- size_t section_header_end =
+ section_header_end =
header.e_shoff + header.e_shnum * header.e_shentsize;
if (section_header_end > data_sp->GetByteSize()) {
data_sp = file.MemoryMapFileContentsIfLocal(file_offset,
@@ -3067,10 +3082,10 @@
s->Printf("e_flags = 0x%8.8x\n", header.e_flags);
s->Printf("e_ehsize = 0x%4.4x\n", header.e_ehsize);
s->Printf("e_phentsize = 0x%4.4x\n", header.e_phentsize);
- s->Printf("e_phnum = 0x%4.4x\n", header.e_phnum);
+ s->Printf("e_phnum = 0x%8.8x\n", header.e_phnum);
s->Printf("e_shentsize = 0x%4.4x\n", header.e_shentsize);
- s->Printf("e_shnum = 0x%4.4x\n", header.e_shnum);
- s->Printf("e_shstrndx = 0x%4.4x\n", header.e_shstrndx);
+ s->Printf("e_shnum = 0x%8.8x\n", header.e_shnum);
+ s->Printf("e_shstrndx = 0x%8.8x\n", header.e_shstrndx);
}
//----------------------------------------------------------------------