linux-kernel - Re: [PATCH] objtool: fix objtool regression on x32 systems

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Date:   Mon, 16 May 2022 17:41:40 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] objtool: fix objtool regression on x32 systems

On Mon, May 16, 2022 at 11:06:36AM -0400, Mikulas Patocka wrote:
> The patch 4abff6d48dbc ("objtool: Fix code relocs vs weak symbols") makes
> the kernel unbootable.  The patch c087c6e7b551 ("objtool: Fix type of
> reloc::addend") attempts to fix it by replacing 'int' with 'long'.
> 
> However, we may be running on a system with x32 ABI and 'long' on x32 is
> 32-bit, thus the patch c087c6e7b551 doesn't really change anything and we
> still end up with miscompiled kernel.  This patch replaces 'long' with
> 'long long', so that the 64-bit kernel is correctly compiled on a x32
> system.

Hurmph.. you're building a 64bit kernel on a x32 hosted machine? And
this is the *only* thing that goes sideways?

I suspect quite a bit of objtool assumes LP64 and won't quite work right
on ILP32 and we've just been lucky so far.

> Index: linux-2.6/tools/objtool/elf.c
> ===================================================================
> --- linux-2.6.orig/tools/objtool/elf.c	2022-05-16 16:20:49.000000000 +0200
> +++ linux-2.6/tools/objtool/elf.c	2022-05-16 16:22:21.000000000 +0200
> @@ -546,7 +546,7 @@ static struct section *elf_create_reloc_
>  						int reltype);
>  
>  int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
> -		  unsigned int type, struct symbol *sym, long addend)
> +		  unsigned int type, struct symbol *sym, long long addend)
>  {
>  	struct reloc *reloc;
>  
> Index: linux-2.6/tools/objtool/include/objtool/elf.h
> ===================================================================
> --- linux-2.6.orig/tools/objtool/include/objtool/elf.h	2022-05-16 16:07:54.000000000 +0200
> +++ linux-2.6/tools/objtool/include/objtool/elf.h	2022-05-16 16:22:45.000000000 +0200
> @@ -73,7 +73,7 @@ struct reloc {
>  	struct symbol *sym;
>  	unsigned long offset;
>  	unsigned int type;
> -	long addend;
> +	long long addend;
>  	int idx;
>  	bool jump_table_start;
>  };
> @@ -135,7 +135,7 @@ struct elf *elf_open_read(const char *na
>  struct section *elf_create_section(struct elf *elf, const char *name, unsigned int sh_flags, size_t entsize, int nr);
>  
>  int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
> -		  unsigned int type, struct symbol *sym, long addend);
> +		  unsigned int type, struct symbol *sym, long long addend);
>  int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,
>  			  unsigned long offset, unsigned int type,
>  			  struct section *insn_sec, unsigned long insn_off);
> 

I think I much prefer s64 there instead of 'long long'. But really I
think all of objtool needs a bit of an audit to see what types need be
used.