linux-kernel - Re: [PATCH 0/5] x86/kallsyms: Fix the call-thunk kallsyms fail

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Date:   Mon, 31 Oct 2022 14:18:13 +0800
From:   Yujie Liu <yujie.liu@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <djwong@...nel.org>, <tglx@...utronix.de>, <jpoimboe@...nel.org>,
        <joao.moreira@...el.com>, <samitolvanen@...gle.com>,
        <lkp@...el.com>
Subject: Re: [PATCH 0/5] x86/kallsyms: Fix the call-thunk kallsyms fail

On Sun, Oct 30, 2022 at 10:15:22AM +0100, Peter Zijlstra wrote:
> On Fri, Oct 28, 2022 at 09:40:22PM +0200, Peter Zijlstra wrote:
> > Hi all,
> > 
> > As reported here:
> > 
> >   https://lkml.kernel.org/r/202210241614.2ae4c1f5-yujie.liu@intel.com
> > 
> > The kallsyms change for call-thunks doesn't really work out as expected. These
> > patches revert that change and propose an alternative.
> 
> Robot found it needed the below; have folded back and pushed out again.

Hi Peter,

We applied the five patches in this patchset plus below extra fixup
patch on top of x86/core branch of tip. The xfstests failure and the
issue of changed dmesg WARNING are gone. Thanks.

  Tested-by: Yujie Liu <yujie.liu@...el.com>

=========================================================================================
compiler/disk/fs/kconfig/rootfs/tbox_group/test/testcase:
  gcc-11/4HDD/xfs/x86_64-rhel-8.3-func/debian-11.1-x86_64-20220510.cgz/lkp-ivb-d04/xfs-no-bug-assert/xfstests

commit:
  f1389181622a0 ("kallsyms: Take callthunks into account")
  9b10b976b8e2f ("x86/kallsyms: Fix the call-thunk kallsyms fail")

f1389181622a08d6 9b10b976b8e2f61d861befc114f
---------------- ---------------------------
       fail:runs  %reproduction    fail:runs
           |             |             |
         12:12        -100%            :12    xfstests.xfs.098.fail
         12:12        -100%            :12    xfstests.xfs.439.fail
           :12          92%          11:12    dmesg.RIP:assfail[xfs]
         12:12        -100%            :12    dmesg.WARNING:CPU:#PID:#at_fs/xfs/xfs_message.c:#xfs_buf_alert_ratelimited.cold-#[xfs]
           :12          92%          11:12    dmesg.WARNING:at_fs/xfs/xfs_message.c:#assfail[xfs]


Best Regards,
Yujie

> 
> ---
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index cf743520a786..55066c493570 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -3479,7 +3479,8 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
>  
>  		if (func && insn_func(insn) && func != insn_func(insn)->pfunc) {
>  			/* Ignore KCFI type preambles, which always fall through */
> -			if (!strncmp(func->name, "__cfi_", 6))
> +			if (!strncmp(func->name, "__cfi_", 6) ||
> +			    !strncmp(func->name, "__pfx_", 6))
>  				return 0;
>  
>  			WARN("%s() falls through to next function %s()",
> @@ -4042,6 +4043,7 @@ static int add_prefix_symbol(struct objtool_file *file, struct symbol *func,
>  
>  	for (;;) {
>  		struct instruction *prev = list_prev_entry(insn, list);
> +		u64 offset;
>  
>  		if (&prev->list == &file->insn_list)
>  			break;
> @@ -4049,11 +4051,13 @@ static int add_prefix_symbol(struct objtool_file *file, struct symbol *func,
>  		if (prev->type != INSN_NOP)
>  			break;
>  
> -		insn = prev;
> -		if (func->offset - prev->offset == opts.prefix) {
> -			elf_create_prefix_symbol(file->elf, func, -opts.prefix);
> +		offset = func->offset - prev->offset;
> +		if (offset >= opts.prefix) {
> +			if (offset == opts.prefix)
> +				elf_create_prefix_symbol(file->elf, func, opts.prefix);
>  			break;
>  		}
> +		insn = prev;
>  	}
>  
>  	return 0;
> diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
> index 9fbdad7a565d..3d636d12d679 100644
> --- a/tools/objtool/elf.c
> +++ b/tools/objtool/elf.c
> @@ -822,7 +822,7 @@ elf_create_section_symbol(struct elf *elf, struct section *sec)
>  static int elf_add_string(struct elf *elf, struct section *strtab, char *str);
>  
>  struct symbol *
> -elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, long addend)
> +elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, long size)
>  {
>  	struct symbol *sym = calloc(1, sizeof(*sym));
>  	size_t namelen = strlen(orig->name) + sizeof("__pfx_");
> @@ -840,7 +840,8 @@ elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, long addend)
>  
>  	sym->sym.st_name = elf_add_string(elf, NULL, name);
>  	sym->sym.st_info = orig->sym.st_info;
> -	sym->sym.st_value = orig->sym.st_value + addend;
> +	sym->sym.st_value = orig->sym.st_value - size;
> +	sym->sym.st_size = size;
>  
>  	sym = __elf_create_symbol(elf, sym);
>  	if (sym)
> diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
> index 9e3bd4717a11..b6974e3173aa 100644
> --- a/tools/objtool/include/objtool/elf.h
> +++ b/tools/objtool/include/objtool/elf.h
> @@ -146,7 +146,7 @@ static inline bool has_multiple_files(struct elf *elf)
>  struct elf *elf_open_read(const char *name, int flags);
>  struct section *elf_create_section(struct elf *elf, const char *name, unsigned int sh_flags, size_t entsize, int nr);
>  
> -struct symbol *elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, long addend);
> +struct symbol *elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, long size);
>  
>  int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
>  		  unsigned int type, struct symbol *sym, s64 addend);