linux-kernel - Re: [RFC PATCH v1 3/3] powerpc: WIP draft support to objtool check

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Date:   Fri, 16 Jun 2023 16:43:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Sathvika Vasireddy <sv@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH v1 3/3] powerpc: WIP draft support to objtool check


Few comments..

On Fri, Jun 16, 2023 at 03:47:52PM +0200, Christophe Leroy wrote:

> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index 0fcf99c91400..f945fe271706 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -236,6 +236,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
>  		"x86_64_start_reservations",
>  		"xen_cpu_bringup_again",
>  		"xen_start_kernel",
> +		"longjmp",
>  	};
>  
>  	if (!func)
> @@ -2060,13 +2061,12 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
>  	 * instruction.
>  	 */
>  	list_for_each_entry_from(reloc, &table->sec->reloc_list, list) {
> -
>  		/* Check for the end of the table: */
>  		if (reloc != table && reloc->jump_table_start)
>  			break;
>  
>  		/* Make sure the table entries are consecutive: */
> -		if (prev_offset && reloc->offset != prev_offset + 8)
> +		if (prev_offset && reloc->offset != prev_offset + 4)

Do we want a global variable (from elf.c) called elf_sizeof_long or so?

>  			break;
>  
>  		/* Detect function pointers from contiguous objects: */
> @@ -2074,7 +2074,10 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
>  		    reloc->addend == pfunc->offset)
>  			break;
>  
> -		dest_insn = find_insn(file, reloc->sym->sec, reloc->addend);
> +		if (table->jump_table_is_rel)
> +			dest_insn = find_insn(file, reloc->sym->sec, reloc->addend + table->offset - reloc->offset);
> +		else
> +			dest_insn = find_insn(file, reloc->sym->sec, reloc->addend);

		offset = reloc->addend;
		if (table->jump_table_is_rel)
			offset += table->offset - reloc->offset;
		dest_insn = find_insn(file, reloc->sym->sec, offset);

perhaps?

>  		if (!dest_insn)
>  			break;
>  
> @@ -4024,6 +4022,11 @@ static bool ignore_unreachable_insn(struct objtool_file *file, struct instructio
>  	if (insn->ignore || insn->type == INSN_NOP || insn->type == INSN_TRAP)
>  		return true;
>  
> +	/* powerpc relocatable files have a word in front of each relocatable function */
> +	if ((file->elf->ehdr.e_machine == EM_PPC || file->elf->ehdr.e_machine == EM_PPC64) &&
> +	    (file->elf->ehdr.e_flags & EF_PPC_RELOCATABLE_LIB) &&
> +	    insn_func(next_insn_same_sec(file, insn)))
> +		return true;

Can't you simply decode that word to INSN_NOP or so?