Adding a new section to an ELF file aborts with Assertion `shdr != NULL'

Adding a new section to an ELF file aborts with Assertion `shdr != NULL'

[Alexander Egorenkov]

Hi all,

i'm facing an issue with libelf when i try to add a new section to an
ELF file.

How to reproduce the issue:
1. Create a simple ELF file with libelf containing only 2 sections, NULL and
a string table
2. Close ELF file
3. Reopen the new ELF file in RW mode with libelf
4. Add new section with elf_newscn()
5. Update ELF with elf_update()
6. Assertion appears

The weird thing is that if i add only a new program segment then
everything goes well. But as soon as i add a new section, it fails.

Error message:

test: elf32_updatenull.c:214: __elf64_updatenull_wrlock: Assertion `shdr
!= NULL' failed.

Any hint what i'm doing wrong ? 

Thank you
Regards
Alex

Re: Adding a new section to an ELF file aborts with Assertion `shdr != NULL'

[Alexander Egorenkov]

Hi all,

Alexander Egorenkov <egorenar-dev@posteo.net> writes:

> Hi all,
>
> i'm facing an issue with libelf when i try to add a new section to an
> ELF file.
>
> How to reproduce the issue:
> 1. Create a simple ELF file with libelf containing only 2 sections, NULL and
> a string table
> 2. Close ELF file
> 3. Reopen the new ELF file in RW mode with libelf
> 4. Add new section with elf_newscn()
> 5. Update ELF with elf_update()
> 6. Assertion appears
>
> The weird thing is that if i add only a new program segment then
> everything goes well. But as soon as i add a new section, it fails.
>
> Error message:
>
> test: elf32_updatenull.c:214: __elf64_updatenull_wrlock: Assertion `shdr
> != NULL' failed.
>
> Any hint what i'm doing wrong ? 
>

One workaround i found is this:

	scn = elf_getscn(elf, 0);
	shdr = elf64_getshdr(scn);

It seems that __elf64_updatenull_wrlock() tries to access the section
header of the NULL section.

Regards
Alex

Re: Adding a new section to an ELF file aborts with Assertion `shdr != NULL'

[Mark Wielaard]

Hi Alex,

On Sat, Sep 04, 2021 at 08:38:51AM +0000, Alexander Egorenkov via Elfutils-devel wrote:
> i'm facing an issue with libelf when i try to add a new section to an
> ELF file.
> 
> How to reproduce the issue:
> 1. Create a simple ELF file with libelf containing only 2 sections, NULL and
> a string table
> 2. Close ELF file
> 3. Reopen the new ELF file in RW mode with libelf
> 4. Add new section with elf_newscn()
> 5. Update ELF with elf_update()
> 6. Assertion appears
> 
> The weird thing is that if i add only a new program segment then
> everything goes well. But as soon as i add a new section, it fails.
> 
> Error message:
> 
> test: elf32_updatenull.c:214: __elf64_updatenull_wrlock: Assertion `shdr
> != NULL' failed.
> 
> Any hint what i'm doing wrong ? 

I don't immediately know. Could you post the code you are using and/or
the generated file after step 2? That might make it a bit easier to
see exactly what is going on.

Thanks,

Mark