linux-kernel - Re: [RFC v4 01/18] objtool: Add abstraction for computation of symbols offsets

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Message-ID: <7bdc1178-e916-7d21-eb54-bea27fcadc17@gmail.com>
Date:   Thu, 22 Aug 2019 17:30:07 +0100
From:   Julien <julien.thierry.kdev@...il.com>
To:     Raphael Gault <raphael.gault@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        jpoimboe@...hat.com
Cc:     peterz@...radead.org, catalin.marinas@....com, will.deacon@....com,
        raph.gault+kdev@...il.com
Subject: Re: [RFC v4 01/18] objtool: Add abstraction for computation of
 symbols offsets

Hi Raphaël,

On 16/08/19 13:23, Raphael Gault wrote:
> The jump destination and relocation offset used previously are only
> reliable on x86_64 architecture. We abstract these computations by calling
> arch-dependent implementations.
> 
> Signed-off-by: Raphael Gault <raphael.gault@....com>
> ---
>   tools/objtool/arch.h            |  6 ++++++
>   tools/objtool/arch/x86/decode.c | 11 +++++++++++
>   tools/objtool/check.c           | 15 ++++++++++-----
>   3 files changed, 27 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h
> index ced3765c4f44..a9a50a25ca66 100644
> --- a/tools/objtool/arch.h
> +++ b/tools/objtool/arch.h
> @@ -66,6 +66,8 @@ struct stack_op {
>   	struct op_src src;
>   };
>   
> +struct instruction;
> +
>   void arch_initial_func_cfi_state(struct cfi_state *state);
>   
>   int arch_decode_instruction(struct elf *elf, struct section *sec,
> @@ -75,4 +77,8 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
>   
>   bool arch_callee_saved_reg(unsigned char reg);
>   
> +unsigned long arch_jump_destination(struct instruction *insn);
> +
> +unsigned long arch_dest_rela_offset(int addend);
> +
>   #endif /* _ARCH_H */
> diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
> index 0567c47a91b1..fa33b3465722 100644
> --- a/tools/objtool/arch/x86/decode.c
> +++ b/tools/objtool/arch/x86/decode.c
> @@ -11,6 +11,7 @@
>   #include "lib/inat.c"
>   #include "lib/insn.c"
>   
> +#include "../../check.h"
>   #include "../../elf.h"
>   #include "../../arch.h"
>   #include "../../warn.h"
> @@ -66,6 +67,11 @@ bool arch_callee_saved_reg(unsigned char reg)
>   	}
>   }
>   
> +unsigned long arch_dest_rela_offset(int addend)
> +{
> +	return addend + 4;
> +}
> +
>   int arch_decode_instruction(struct elf *elf, struct section *sec,
>   			    unsigned long offset, unsigned int maxlen,
>   			    unsigned int *len, enum insn_type *type,
> @@ -497,3 +503,8 @@ void arch_initial_func_cfi_state(struct cfi_state *state)
>   	state->regs[16].base = CFI_CFA;
>   	state->regs[16].offset = -8;
>   }
> +
> +unsigned long arch_jump_destination(struct instruction *insn)
> +{
> +	return insn->offset + insn->len + insn->immediate;
> +}
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index 176f2f084060..479fab46b656 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -563,7 +563,7 @@ static int add_jump_destinations(struct objtool_file *file)
>   					       insn->len);
>   		if (!rela) {
>   			dest_sec = insn->sec;
> -			dest_off = insn->offset + insn->len + insn->immediate;
> +			dest_off = arch_jump_destination(insn);
>   		} else if (rela->sym->type == STT_SECTION) {
>   			dest_sec = rela->sym->sec;
>   			dest_off = rela->addend + 4;
> @@ -659,7 +659,7 @@ static int add_call_destinations(struct objtool_file *file)
>   		rela = find_rela_by_dest_range(insn->sec, insn->offset,
>   					       insn->len);
>   		if (!rela) {
> -			dest_off = insn->offset + insn->len + insn->immediate;
> +			dest_off = arch_jump_destination(insn);
>   			insn->call_dest = find_symbol_by_offset(insn->sec,
>   								dest_off);
>   
> @@ -672,14 +672,19 @@ static int add_call_destinations(struct objtool_file *file)
>   			}
>   
>   		} else if (rela->sym->type == STT_SECTION) {
> +			/*
> +			 * the original x86_64 code adds 4 to the rela->addend
> +			 * which is not needed on arm64 architecture.
> +			 */

I'm not sure this is worth mentioning in generic code. You might include 
it in the commit message to justify the change.

> +			dest_off = arch_dest_rela_offset(rela->addend);
>   			insn->call_dest = find_symbol_by_offset(rela->sym->sec,
> -								rela->addend+4);
> +								dest_off);
>   			if (!insn->call_dest ||
>   			    insn->call_dest->type != STT_FUNC) {
> -				WARN_FUNC("can't find call dest symbol at %s+0x%x",
> +				WARN_FUNC("can't find call dest symbol at %s+0x%lx",
>   					  insn->sec, insn->offset,
>   					  rela->sym->sec->name,
> -					  rela->addend + 4);
> +					  dest_off);
>   				return -1;
>   			}
>   		} else
> 

Otherwise, the change looks good to me.

Thanks,

-- 
Julien Thierry