[PATCH] D64913: [yaml2obj] - Add a support for defining null sections in YAMLs.

[George Rimar via Phabricator via llvm-commits]

grimar created this revision.
grimar added reviewers: jhenderson, MaskRay.
Herald added a subscriber: jakehehrlich.

ELF spec shows (Figure 4-10: Section Header Table Entry:Index 0,
http://www.sco.com/developers/gabi/latest/ch4.sheader.html)
that section header at index 0 (null section) can have `sh_size` and
`sh_link` fields set to non-zero values.

It says (https://docs.oracle.com/cd/E19683-01/817-3677/6mj8mbtc9/index.html):

> If the number of sections is greater than or equal to SHN_LORESERVE (0xff00),
>  this member has the value zero and the actual number of section header table
>  entries is contained in the sh_size field of the section header at index 0.
>  Otherwise, the sh_size member of the initial entry contains 0.

and:

> If the section name string table section index is greater than or equal to SHN_LORESERVE
>  (0xff00), this member has the value SHN_XINDEX (0xffff) and the actual index of the section
>  name string table section is contained in thesh_link field of the section header at index 0.
>  Otherwise, the sh_link member of the initial entry contains 0.

At this moment it is not possible to create custom section headers at index 0 using yaml2obj.
This patch implements this.


https://reviews.llvm.org/D64913

Files:
  test/tools/yaml2obj/elf-custom-null-section.yaml
  tools/yaml2obj/yaml2elf.cpp

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