linux-kernel - Re: [PATCH 3/3] objtool: Enable compilation of objtool for all architectures

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Date:   Wed, 27 May 2020 20:12:51 +0530
From:   Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Matt Helsley <mhelsley@...are.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Julien Thierry <jthierry@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 3/3] objtool: Enable compilation of objtool for all
 architectures

[...]

> From: Matt Helsley <mhelsley@...are.com>
> Subject: [PATCH] objtool: Enable compilation of objtool for all architectures
> 
> Objtool currently only compiles for x86 architectures. This is
> fine as it presently does not support tooling for other
> architectures. However, we would like to be able to convert other
> kernel tools to run as objtool sub commands because they too
> process ELF object files. This will allow us to convert tools
> such as recordmcount to use objtool's ELF code.
> 
> Since much of recordmcount's ELF code is copy-paste code to/from
> a variety of other kernel tools (look at modpost for example) this
> means that if we can convert recordmcount we can convert more.
> 
> We define weak definitions for subcommand entry functions and other weak
> definitions for shared functions critical to building existing
> subcommands. These return 127 when the command is missing which signify
> tools that do not exist on all architectures.  In this case the "check"
> and "orc" tools do not exist on all architectures so we only add them
> for x86. Future changes adding support for "check", to arm64 for
> example, can then modify the SUBCMD_CHECK variable when building for
> arm64.
> 
> Objtool is not currently wired in to KConfig to be built for other
> architectures because it's not needed for those architectures and
> there are no commands it supports other than those for x86. As more
> command support is enabled on various architectures the necessary
> KConfig changes can be made (e.g. adding "STACK_VALIDATION") to
> trigger building objtool.
> 
> [ jpoimboe: remove aliases, add __weak macro, add error messages ]
> 
> Cc: Julien Thierry <jthierry@...hat.com>
> Signed-off-by: Matt Helsley <mhelsley@...are.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>


A minor nit-pick in objtool.h

Reviewed-by: Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>

> ---
[...]

> diff --git a/tools/objtool/objtool.h b/tools/objtool/objtool.h
> index d89616b2ca39..528028a66816 100644
> --- a/tools/objtool/objtool.h
> +++ b/tools/objtool/objtool.h
> @@ -19,4 +19,9 @@ struct objtool_file {
>  	bool ignore_unreachables, c_file, hints, rodata;
>  };
> 
> +int check(const char *objname, bool orc);
> +int orc_dump(const char *objname);
> +int create_orc(struct objtool_file *file);
> +int create_orc_sections(struct objtool_file *file);
> +
>  #endif /* _OBJTOOL_H */

above hunk will not apply cleanly on patch 2 of the series, it expects
a new line after struct objtool which is missing in patch 2. 

-- 
Kamalesh