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RFC: [PATCH] ELF: Don't require section header on ELF objects

H.J. Lu hjl.tools@gmail.com
Sun Mar 8 18:06:33 GMT 2020 
On Sun, Mar 8, 2020 at 10:59 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> Any comments?
>
> Kaylee, do you have copyright paper with FSF?
>
> H.J.
> ---
> Section header isn't mandatory on ELF executable nor shared library.
> This patch adds a new linker option, -z nosectionheader, to omit ELF
> section header when building an executable or shared library, adds
> an objcopy and strip option, --remove-section-header, to remove ELF
> section header from an executable or shared library.
>
> The PT_DYNAMIC segment contains DT_HASH/DT_GNU_HASH/DT_MIPS_XHASH,
> DT_STRTAB, DT_SYMTAB, DT_STRSZ and DT_SYMENT, which can be used to
> reconstruct dynamic symbol table when section header isn't available.
> For DT_HASH, the number of dynamic symbol table entries equals the
> number of chains.  For DT_GNU_HASH/DT_MIPS_XHASH, only defined symbols
> with non-STB_LOCAL indings are in hash table.  Since in dynamic symbol
> table, all symbols with STB_LOCAL binding are placed before symbols with
> other bindings and all defined symbols are placed before undefined ones,

It should read

---
all symbols with STB_LOCAL binding are placed
before symbols with other bindings and all undefined symbols are placed
before defined ones,
---

The complete patch set is on users/hjl/pr25617/master branch at

https://gitlab.com/x86-binutils/binutils-gdb

> the highest symbol index in DT_GNU_HASH/DT_MIPS_XHASH is the highest
> dynamic symbol table index.
>
> bfd/
>
> 2020-03-XX  H.J. Lu  <hongjiu.lu@intel.com>
>             Kaylee Blake  <klkblake@gmail.com>
>
>         PR ld/25617
>         * bfd.c (BFD_NO_SECTION_HEADER): New.
>         (BFD_FLAGS_SAVED): Add BFD_NO_SECTION_HEADER.
>         (BFD_FLAGS_FOR_BFD_USE_MASK): Likewise.
>         * elfcode.h (elf_swap_ehdr_out): Omit section header on
>         non-relocatable output with BFD_NO_SECTION_HEADER.
>         (elf_write_shdrs_and_ehdr): Likewise.
>         * elfxx-target.h (TARGET_BIG_SYM): Add BFD_NO_SECTION_HEADER
>         to object_flags.
>         (TARGET_LITTLE_SYM): Likewise.
>         * bfd-in2.h: Regenerated.
>
> binutils/
>
> 2020-03-XX  H.J. Lu  <hongjiu.lu@intel.com>
>
>         PR ld/25617
>         * NEWS: Mention --remove-section-header for objcopy and strip.
>         * doc/binutils.texi: Document --remove-section-header for objcopy
>         and strip.
>         * objcopy.c (remove_section_header): New.
>         (command_line_switch): Add OPTION_REMOVE_SECTION_HEADER.
>         (strip_options): Add --remove-section-header.
>         (copy_options): Likewise.
>         (copy_usage): Add --remove-section-header.
>         (strip_usage): Likewise.
>         (copy_object): Renamed to ...
>         (copy_object_1): This.  Issue a warning for
>         --remove-section-header on non-ELF targets.
>         (copy_object): New.
>         (strip_main): Handle OPTION_REMOVE_SECTION_HEADER.
>         (copy_main): Likewise.
>


-- 
H.J.
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