DW_DLE_TOO_FEW_SECTIONS Error for ELF files with no SHDRs

[rvijayc]

It is quite valid to have an ELF file with program headers only and no section headers (for example, core dumps). But, the following code raises a DW_DLV_TOO_FEW_SECTIONS error for such files.

https://github.com/davea42/libdwarf-code/blob/c0cfba34ec80996426b5be2523f6447a2c9b7b39/src/lib/libdwarf/dwarf_elf_load_headers.c#L213-L216

Wouldn't it be better to handle this gracefully by returning DW_DLV_NO_ENTRY instead of DW_DLV_ERROR? I believe this is what the older versions of libdwarf used to return when we called dwarf_elf_init. I don't believe this should be an error. Please correct me if I missed anything.

Appreciate your help! Thank you.

[davea42]

You are correct, this was a mistake on my part.

According to the Elf generic ABI e_shoff of zero means there are no sections.

the following patch is untested, but I will test now and push this soonish.

-- a/src/lib/libdwarf/dwarf_elf_load_headers.c
+++ b/src/lib/libdwarf/dwarf_elf_load_headers.c
@@ -210,8 +210,11 @@ generic_ehdr_from_32(dwarf_elf_object_access_internals_t *ep,
     ASNAR(ep->f_copy_word,ehdr->ge_shentsize,e->e_shentsize);
     ASNAR(ep->f_copy_word,ehdr->ge_shnum,e->e_shnum);
     ASNAR(ep->f_copy_word,ehdr->ge_shstrndx,e->e_shstrndx);
+    if (!ehdr->ge_shoff) {
+        return DW_DLV_NO_ENTRY;
+    }
     if (ehdr->ge_shoff < sizeof(dw_elf32_ehdr)) {
-        /* zero or offset is inside the header! */
+        /* offset is inside the header! */

I will also patch one of my small test objects to put in a zero e_shoff to ensure the right thing happens.

Thanks for pointing this out. Lets leave this open until it is actually fixed...

[rvijayc]

Thanks for your response. I assume this will apply to other similar checks as well? For example:

https://github.com/davea42/libdwarf-code/blob/c0cfba34ec80996426b5be2523f6447a2c9b7b39/src/lib/libdwarf/dwarf_elf_load_headers.c#L222-L225

https://github.com/davea42/libdwarf-code/blob/c0cfba34ec80996426b5be2523f6447a2c9b7b39/src/lib/libdwarf/dwarf_elf_load_headers.c#L233-L236

Although, we may never hit this for ELF files with no sections header (we'll bail out earlier on the shoff check).

[davea42]

What is at line 222 is detecting corrupt dwarf, and is an error.

I created an object with zeroed e_shoff in regressiontests so we have an ongoing test of that specific issue.

Changes pushed to github.

[davea42]

The changes are in today's v0.9.1 release.

[davea42]

Since (I believe) this is fixed, I am closing. I have two test objects now for regression testing, each with e_shoff zero. One Elf32 the other Elf64.