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;
}