linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Sami Tolvanen <samitolvanen@google.com>
To: Padmanabha Srinivasaiah <treasure4paddy@gmail.com>
Cc: Jessica Yu <jeyu@kernel.org>, Kees Cook <keescook@chromium.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Miroslav Benes <mbenes@suse.cz>, Petr Mladek <pmladek@suse.com>,
	Miguel Ojeda <ojeda@kernel.org>, Joe Perches <joe@perches.com>,
	Stephen Boyd <swboyd@chromium.org>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH v2] kallsyms: strip ThinLTO postfix ".cfi_jt"
Date: Wed, 28 Jul 2021 13:57:21 -0700	[thread overview]
Message-ID: <CABCJKudYRiK0KcMHGHeBFcr+Smwa9EM+NFeBpMo_ePqK+zHz0w@mail.gmail.com> (raw)
In-Reply-To: <20210727140618.19130-1-treasure4paddy@gmail.com>

Hi,

On Tue, Jul 27, 2021 at 7:07 AM Padmanabha Srinivasaiah
<treasure4paddy@gmail.com> wrote:
>
> Clang ThinLTO adds a postfix ".cfi_jt" to a symbols of extern functions.

These symbols are added with CONFIG_CFI_CLANG no matter which LTO mode
is selected, so talking about ThinLTO here isn't quite correct.

> For example this breaks syscall tracer that doesn't expect such postfix,
> so strip out the postfix from the output.
>
> Signed-off-by: Padmanabha Srinivasaiah <treasure4paddy@gmail.com>
> ---
> Change in v2:
>   - Use existing routine in kallsyms to strip postfix ".cfi_jt" from
>     extern function name.
>   - Modified the commit message accordingly
>
>  kernel/kallsyms.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 0ba87982d017..e9148626ae6c 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -166,16 +166,20 @@ static unsigned long kallsyms_sym_address(int idx)
>
>  #if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN)
>  /*
> - * LLVM appends a hash to static function names when ThinLTO and CFI are
> - * both enabled, i.e. foo() becomes foo$707af9a22804d33c81801f27dcfe489b.
> - * This causes confusion and potentially breaks user space tools, so we
> - * strip the suffix from expanded symbol names.
> + * LLVM appends a hash to static function names and just ".cfi_jt" postfix
> + * for non-static functions when both ThinLTO and CFI are enabled,

Functions aren't technically speaking renamed to add a .cfi_jt
postfix. Instead, these are separate symbols that point to the CFI
jump table. Perhaps the comment should just say that we want to strip
.cfi_jt from CFI jump table symbols?

> + * i.e. for example foo() becomes foo$707af9a22804d33c81801f27dcfe489b.
> + * This causes confusion and potentially breaks user space tools and
> + * built-in components, so we strip the suffix from expanded symbol names.
>   */
>  static inline bool cleanup_symbol_name(char *s)
>  {
>         char *res;
>
>         res = strrchr(s, '$');
> +       if (!res)
> +               res = strstr(s, ".cfi_jt");
> +
>         if (res)
>                 *res = '\0';

This looks otherwise fine to me, but it's going to conflict with
Nick's earlier patch:

https://lore.kernel.org/lkml/20210707181814.365496-1-ndesaulniers@google.com/

Could you please rebase this on top of that, and take into account
that we should do this when CONFIG_LTO_CLANG is enabled, not only with
LTO_CLANG_THIN?

Sami

  reply	other threads:[~2021-07-28 20:57 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20210727131853.GA18032@pswork>
2021-07-27 14:06 ` Padmanabha Srinivasaiah
2021-07-28 20:57   ` Sami Tolvanen [this message]
2021-07-29 15:29     ` Padmanabha Srinivasaiah
2021-07-29 20:53     ` [PATCH v3] kallsyms: strip CLANG CFI " Padmanabha Srinivasaiah
2021-08-03 16:28       ` Sami Tolvanen
2021-08-04 17:17         ` Padmanabha Srinivasaiah
2021-08-05 23:27         ` [PATCH v4] " Padmanabha Srinivasaiah
2021-08-12 23:05           ` Sami Tolvanen
2021-08-14 12:15             ` Padmanabha Srinivasaiah
2021-08-14 12:42             ` [PATCH v5] " Padmanabha Srinivasaiah
2021-10-01 18:29               ` Nick Desaulniers

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CABCJKudYRiK0KcMHGHeBFcr+Smwa9EM+NFeBpMo_ePqK+zHz0w@mail.gmail.com \
    --to=samitolvanen@google.com \
    --cc=clang-built-linux@googlegroups.com \
    --cc=gustavoars@kernel.org \
    --cc=jeyu@kernel.org \
    --cc=joe@perches.com \
    --cc=keescook@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mbenes@suse.cz \
    --cc=nathan@kernel.org \
    --cc=ndesaulniers@google.com \
    --cc=ojeda@kernel.org \
    --cc=pmladek@suse.com \
    --cc=swboyd@chromium.org \
    --cc=treasure4paddy@gmail.com \
    --subject='Re: [PATCH v2] kallsyms: strip ThinLTO postfix ".cfi_jt"' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).