Re: [PATCH] kallsyms: Fix kallsyms_selftest failure

[Leizhen (ThunderTown)]

On 2023/8/25 11:46, Yonghong Song wrote:
> Kernel test robot reported a kallsyms_test failure when clang lto is
> enabled (thin or full) and CONFIG_KALLSYMS_SELFTEST is also enabled.
> I can reproduce in my local environment with the following error message
> with thin lto:
>   [    1.877897] kallsyms_selftest: Test for 1750th symbol failed: (tsc_cs_mark_unstable) addr=ffffffff81038090
>   [    1.877901] kallsyms_selftest: abort
> 
> It appears that commit 8cc32a9bbf29 ("kallsyms: strip LTO-only suffixes
> from promoted global functions") caused the failure. Commit 8cc32a9bbf29
> changed cleanup_symbol_name() based on ".llvm." instead of '.' where
> ".llvm." is appended to a before-lto-optimization local symbol name.
> We need to propagate such knowledge in kallsyms_selftest.c as well.
> 
> Further more, compare_symbol_name() in kallsyms.c needs change as well.
> In scripts/kallsyms.c, kallsyms_names and kallsyms_seqs_of_names are used
> to record symbol names themselves and index to symbol names respectively.
> For example:
>   kallsyms_names:
>     ...
>     __amd_smn_rw._entry       <== seq 1000
>     __amd_smn_rw._entry.5     <== seq 1001
>     __amd_smn_rw.llvm.<hash>  <== seq 1002
>     ...
> 
> kallsyms_seqs_of_names are sorted based on cleanup_symbol_name() through, so
> the order in kallsyms_seqs_of_names actually has
> 
>   index 1000:   seq 1002   <== __amd_smn_rw.llvm.<hash> (actual symbol comparison using '__amd_smn_rw')
>   index 1001:   seq 1000   <== __amd_smn_rw._entry
>   index 1002:   seq 1001   <== __amd_smn_rw._entry.5
> 
> Let us say at a particular point, at index 1000, symbol '__amd_smn_rw.llvm.<hash>'
> is comparing to '__amd_smn_rw._entry' where '__amd_smn_rw._entry' is the one to
> search e.g., with function kallsyms_on_each_match_symbol(). The current implementation
> will find out '__amd_smn_rw._entry' is less than '__amd_smn_rw.llvm.<hash>' and
> then continue to search e.g., index 999 and never found a match although the actual
> index 1001 is a match.
> 
> To fix this issue, let us do cleanup_symbol_name() first and then do comparison.
> In the above case, comparing '__amd_smn_rw' vs '__amd_smn_rw._entry' and
> '__amd_smn_rw._entry' being greater than '__amd_smn_rw', the next comparison will
> be > index 1000 and eventually index 1001 will be hit an a match is found.
> 
> For any symbols not having '.llvm.' substr, there is no functionality change
> for compare_symbol_name().

Reviewed-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>

> 
> Fixes: 8cc32a9bbf29 ("kallsyms: strip LTO-only suffixes from promoted global functions")
> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-lkp/202308232200.1c932a90-oliver.sang@xxxxxxxxx
> Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
> ---
>  kernel/kallsyms.c          | 17 +++++++----------
>  kernel/kallsyms_selftest.c | 23 +----------------------
>  2 files changed, 8 insertions(+), 32 deletions(-)
> 
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 016d997131d4..e12d26c10dba 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -188,16 +188,13 @@ static bool cleanup_symbol_name(char *s)
>  
>  static int compare_symbol_name(const char *name, char *namebuf)
>  {
> -	int ret;
> -
> -	ret = strcmp(name, namebuf);
> -	if (!ret)
> -		return ret;
> -
> -	if (cleanup_symbol_name(namebuf) && !strcmp(name, namebuf))
> -		return 0;
> -
> -	return ret;
> +	/* The kallsyms_seqs_of_names is sorted based on names after
> +	 * cleanup_symbol_name() (see scripts/kallsyms.c) if clang lto is enabled.
> +	 * To ensure correct bisection in kallsyms_lookup_names(), do
> +	 * cleanup_symbol_name(namebuf) before comparing name and namebuf.
> +	 */
> +	cleanup_symbol_name(namebuf);
> +	return strcmp(name, namebuf);
>  }
>  
>  static unsigned int get_symbol_seq(int index)
> diff --git a/kernel/kallsyms_selftest.c b/kernel/kallsyms_selftest.c
> index a2e3745d15c4..e05ddc33a752 100644
> --- a/kernel/kallsyms_selftest.c
> +++ b/kernel/kallsyms_selftest.c
> @@ -196,7 +196,7 @@ static bool match_cleanup_name(const char *s, const char *name)
>  	if (!IS_ENABLED(CONFIG_LTO_CLANG))
>  		return false;
>  
> -	p = strchr(s, '.');
> +	p = strstr(s, ".llvm.");
>  	if (!p)
>  		return false;
>  
> @@ -344,27 +344,6 @@ static int test_kallsyms_basic_function(void)
>  			goto failed;
>  		}
>  
> -		/*
> -		 * The first '.' may be the initial letter, in which case the
> -		 * entire symbol name will be truncated to an empty string in
> -		 * cleanup_symbol_name(). Do not test these symbols.
> -		 *
> -		 * For example:
> -		 * cat /proc/kallsyms | awk '{print $3}' | grep -E "^\." | head
> -		 * .E_read_words
> -		 * .E_leading_bytes
> -		 * .E_trailing_bytes
> -		 * .E_write_words
> -		 * .E_copy
> -		 * .str.292.llvm.12122243386960820698
> -		 * .str.24.llvm.12122243386960820698
> -		 * .str.29.llvm.12122243386960820698
> -		 * .str.75.llvm.12122243386960820698
> -		 * .str.99.llvm.12122243386960820698
> -		 */
> -		if (IS_ENABLED(CONFIG_LTO_CLANG) && !namebuf[0])
> -			continue;
> -
>  		lookup_addr = kallsyms_lookup_name(namebuf);
>  
>  		memset(stat, 0, sizeof(*stat));
> 

-- 
Regards,
  Zhen Lei