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Message-ID: <3be436cf49b8850b95eb74ce7b7c45e05bc4ad82.camel@suse.com>
Subject: Re: [PATCH v1 5/5] documentation: Update on livepatch elf format
From: Marcos Paulo de Souza <mpdesouza@suse.com>
To: Lukas Hruska <lhruska@suse.cz>, Petr Mladek <pmladek@suse.com>, Miroslav
	Benes <mbenes@suse.cz>, Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Joe Lawrence <joe.lawrence@redhat.com>, live-patching@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org
Date: Wed, 10 Jan 2024 16:54:48 -0300
In-Reply-To: <20231106162513.17556-6-lhruska@suse.cz>
References: <20231106162513.17556-1-lhruska@suse.cz>
	 <20231106162513.17556-6-lhruska@suse.cz>
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On Mon, 2023-11-06 at 17:25 +0100, Lukas Hruska wrote:
> Add a section to Documentation/livepatch/module-elf-format.rst
> describing how klp-convert works for fixing relocations.
>=20
> Signed-off-by: Lukas Hruska <lhruska@suse.cz>

Reviewed-by: Marcos Paulo de Souza <mpdesouza@suse.com>

> ---
> =C2=A0Documentation/livepatch/module-elf-format.rst | 67
> +++++++++++++++++++
> =C2=A01 file changed, 67 insertions(+)
>=20
> diff --git a/Documentation/livepatch/module-elf-format.rst
> b/Documentation/livepatch/module-elf-format.rst
> index a03ed02ec57e..2aa9b11cd806 100644
> --- a/Documentation/livepatch/module-elf-format.rst
> +++ b/Documentation/livepatch/module-elf-format.rst
> @@ -300,3 +300,70 @@ symbol table, and relocation section indices,
> ELF information is preserved for
> =C2=A0livepatch modules and is made accessible by the module loader
> through
> =C2=A0module->klp_info, which is a :c:type:`klp_modinfo` struct. When a
> livepatch module
> =C2=A0loads, this struct is filled in by the module loader.
> +
> +6. klp-convert tool
> +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> +The livepatch relocation sections might be created using
> +scripts/livepatch/klp-convert. It is called automatically during
> +the build as part of a module post processing.
> +
> +The tool is not able to find the symbols and all the metadata
> +automatically. Instead, all needed information must already be
> +part of rela entry for the given symbol. Such a rela can
> +be created easily by using KLP_RELOC_SYMBOL() macro after
> +the symbol declaration.
> +
> +KLP_RELOC_SYMBOL causes that the relocation entries for
> +the given symbol will be created in the following format::
> +
> +=C2=A0 .klp.sym.rela.lp_object.sym_object.sym_name,sympos
> +=C2=A0 ^=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ^ ^=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ^ ^=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0 ^ ^=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ^=C2=A0=C2=A0 ^
> +=C2=A0 |___________| |_______| |________| |______|=C2=A0=C2=A0 |
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 [A]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 [B]=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 [C]=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 [D]=C2=A0=C2=A0=C2=A0 [E]
> +
> +[A]
> +=C2=A0 The symbol name is prefixed with the string ".klp.sym.rela."
> +
> +[B]
> +=C2=A0 The name of the object (i.e. "vmlinux" or name of module) which
> +=C2=A0 is livepatched.
> +
> +[C]
> +=C2=A0 The name of the object (i.e. "vmlinux" or name of module) to
> +=C2=A0 which the symbol belongs follows immediately after the prefix.
> +
> +[D]
> +=C2=A0 The actual name of the symbol.
> +
> +[E]
> +=C2=A0 The position of the symbol in the object (as according to
> kallsyms)
> +=C2=A0 This is used to differentiate duplicate symbols within the same
> +=C2=A0 object. The symbol position is expressed numerically (0, 1, 2...)=
.
> +=C2=A0 The symbol position of a unique symbol is 0.
> +
> +Example:
> +--------
> +**Livepatch source code:**
> +
> +::
> +
> +=C2=A0 extern char *saved_command_line \
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0 KLP_RELOC_SYMBOL(vmlinux, vmlinux,
> saved_command_line, 0);
> +
> +**`readelf -r -W` output of compiled module:**
> +
> +::
> +
> +=C2=A0 Relocation section '.rela.text' at offset 0x32e60 contains 10
> entries:
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Offset=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Info=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Type=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0
> Symbol's Value=C2=A0 Symbol's Name + Addend
> +=C2=A0 ...
> +=C2=A0 0000000000000068=C2=A0 0000003c00000002 R_X86_64_PC32=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0
> 0000000000000000 .klp.sym.rela.vmlinux.vmlinux.saved_command_line,0 -
> 4
> +=C2=A0 ...
> +
> +**`readelf -r -W` output of transformed module by klp-convert:**
> +
> +::
> +
> +=C2=A0 Relocation section '.klp.rela.vmlinux.text' at offset 0x5cb60
> contains 1 entry:
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Offset=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Info=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Type=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0
> Symbol's Value=C2=A0 Symbol's Name + Addend
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 0000000000000068=C2=A0 0000003c00000002 R=
_X86_64_PC32=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0
> 0000000000000000 .klp.sym.vmlinux.saved_command_line,0 - 4