linux-kernel - Re: [POC 22/23] livepatch/module: Remove obsolete copy_module

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Date:   Fri, 3 Apr 2020 14:03:28 -0400
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        Nicolai Stange <nstange@...e.de>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [POC 22/23] livepatch/module: Remove obsolete copy_module_elf()

On Fri, Jan 17, 2020 at 04:03:22PM +0100, Petr Mladek wrote:
> The split livepatch modules can be relocated immedidately when they
> are loaded. There is no longer needed to preserve the elf sections.
> 
> Signed-off-by: Petr Mladek <pmladek@...e.com>
> ---
>  Documentation/livepatch/module-elf-format.rst | 18 ++++++
>  include/linux/module.h                        |  3 -
>  kernel/module.c                               | 87 ---------------------------
>  3 files changed, 18 insertions(+), 90 deletions(-)
> 
> diff --git a/Documentation/livepatch/module-elf-format.rst b/Documentation/livepatch/module-elf-format.rst
> index 9f0c997d4940..8c6b894c4661 100644
> --- a/Documentation/livepatch/module-elf-format.rst
> +++ b/Documentation/livepatch/module-elf-format.rst
> @@ -14,6 +14,7 @@ This document outlines the Elf format requirements that livepatch modules must f
>     4. Livepatch symbols
>        4.1 A livepatch module's symbol table
>        4.2 Livepatch symbol format
> +   5. Symbol table and Elf section access
>  
>  1. Background and motivation
>  ============================
> @@ -295,3 +296,20 @@ See include/uapi/linux/elf.h for the actual definitions.
>  [*]
>    Note that the 'Ndx' (Section index) for these symbols is SHN_LIVEPATCH (0xff20).
>    "OS" means OS-specific.
> +
> +5. Symbol table and Elf section access
> +======================================
> +A livepatch module's symbol table is accessible through module->symtab.
> +
> +Since apply_relocate_add() requires access to a module's section headers,
> +symbol table, and relocation section indices, Elf information is preserved for
> +livepatch modules and is made accessible by the module loader through
> +module->klp_info, which is a klp_modinfo struct. When a livepatch module loads,
> +this struct is filled in by the module loader. Its fields are documented below::
> +
> +	struct klp_modinfo {
> +		Elf_Ehdr hdr; /* Elf header */
> +		Elf_Shdr *sechdrs; /* Section header table */
> +		char *secstrings; /* String table for the section headers */
> +		unsigned int symndx; /* The symbol table section index */
> +	};

I think this file was inadvertently reverted, or at least the Symbol
table and Elf section access section was supposed to stay gone, right?

-- Joe