kernel/kallsyms.c | 5 ++--- scripts/kallsyms.c | 6 +++--- 2 files changed, 5 insertions(+), 6 deletions(-)
Commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
stripped all function/variable suffixes started with '.' regardless
of whether those suffixes are generated at LTO mode or not. In fact,
as far as I know, in LTO mode, when a static function/variable is
promoted to the global scope, '.llvm.<...>' suffix is added.
The existing mechanism breaks live patch for a LTO kernel even if
no <symbol>.llvm.<...> symbols are involved. For example, for the following
kernel symbols:
$ grep bpf_verifier_vlog /proc/kallsyms
ffffffff81549f60 t bpf_verifier_vlog
ffffffff8268b430 d bpf_verifier_vlog._entry
ffffffff8282a958 d bpf_verifier_vlog._entry_ptr
ffffffff82e12a1f d bpf_verifier_vlog.__already_done
'bpf_verifier_vlog' is a static function. '_entry', '_entry_ptr' and
'__already_done' are static variables used inside 'bpf_verifier_vlog',
so llvm promotes them to file-level static with prefix 'bpf_verifier_vlog.'.
Note that the func-level to file-level static function promotion also
happens without LTO.
Given a symbol name 'bpf_verifier_vlog', with LTO kernel, current mechanism will
return 4 symbols to live patch subsystem which current live patching
subsystem cannot handle it. With non-LTO kernel, only one symbol
is returned.
In [1], we have a lengthy discussion, the suggestion is to separate two
cases:
(1). new symbols with suffix which are generated regardless of whether
LTO is enabled or not, and
(2). new symbols with suffix generated only when LTO is enabled.
The cleanup_symbol_name() should only remove suffixes for case (2).
Case (1) should not be changed so it can work uniformly with or without LTO.
This patch removed LTO-only suffix '.llvm.<...>' so live patching and
tracing should work the same way for non-LTO kernel.
The cleanup_symbol_name() in scripts/kallsyms.c is also changed to have the same
filtering pattern so both kernel and kallsyms tool have the same
expectation on the order of symbols.
[1] https://lore.kernel.org/live-patching/20230615170048.2382735-1-song@kernel.org/T/#u
Fixes: 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
Reported-by: Song Liu <song@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
kernel/kallsyms.c | 5 ++---
scripts/kallsyms.c | 6 +++---
2 files changed, 5 insertions(+), 6 deletions(-)
Changelogs:
v1 -> v2:
. add 'Reported-by: Song Liu <song@kernel.org>'
. also fix in scripts/kallsyms.c.
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 77747391f49b..4874508bb950 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -174,11 +174,10 @@ static bool cleanup_symbol_name(char *s)
* LLVM appends various suffixes for local functions and variables that
* must be promoted to global scope as part of LTO. This can break
* hooking of static functions with kprobes. '.' is not a valid
- * character in an identifier in C. Suffixes observed:
+ * character in an identifier in C. Suffixes only in LLVM LTO observed:
* - foo.llvm.[0-9a-f]+
- * - foo.[0-9a-f]+
*/
- res = strchr(s, '.');
+ res = strstr(s, ".llvm.");
if (res) {
*res = '\0';
return true;
diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 0d2db41177b2..13af6d0ff845 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -346,10 +346,10 @@ static void cleanup_symbol_name(char *s)
* ASCII[_] = 5f
* ASCII[a-z] = 61,7a
*
- * As above, replacing '.' with '\0' does not affect the main sorting,
- * but it helps us with subsorting.
+ * As above, replacing the first '.' in ".llvm." with '\0' does not
+ * affect the main sorting, but it helps us with subsorting.
*/
- p = strchr(s, '.');
+ p = strstr(s, ".llvm.");
if (p)
*p = '\0';
}
--
2.34.1
On 2023/6/29 2:19, Yonghong Song wrote:
> Commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
> stripped all function/variable suffixes started with '.' regardless
> of whether those suffixes are generated at LTO mode or not. In fact,
> as far as I know, in LTO mode, when a static function/variable is
> promoted to the global scope, '.llvm.<...>' suffix is added.
>
> The existing mechanism breaks live patch for a LTO kernel even if
> no <symbol>.llvm.<...> symbols are involved. For example, for the following
> kernel symbols:
> $ grep bpf_verifier_vlog /proc/kallsyms
> ffffffff81549f60 t bpf_verifier_vlog
> ffffffff8268b430 d bpf_verifier_vlog._entry
> ffffffff8282a958 d bpf_verifier_vlog._entry_ptr
> ffffffff82e12a1f d bpf_verifier_vlog.__already_done
> 'bpf_verifier_vlog' is a static function. '_entry', '_entry_ptr' and
> '__already_done' are static variables used inside 'bpf_verifier_vlog',
> so llvm promotes them to file-level static with prefix 'bpf_verifier_vlog.'.
> Note that the func-level to file-level static function promotion also
> happens without LTO.
>
> Given a symbol name 'bpf_verifier_vlog', with LTO kernel, current mechanism will
> return 4 symbols to live patch subsystem which current live patching
> subsystem cannot handle it. With non-LTO kernel, only one symbol
> is returned.
>
> In [1], we have a lengthy discussion, the suggestion is to separate two
> cases:
> (1). new symbols with suffix which are generated regardless of whether
> LTO is enabled or not, and
> (2). new symbols with suffix generated only when LTO is enabled.
>
> The cleanup_symbol_name() should only remove suffixes for case (2).
> Case (1) should not be changed so it can work uniformly with or without LTO.
>
> This patch removed LTO-only suffix '.llvm.<...>' so live patching and
> tracing should work the same way for non-LTO kernel.
> The cleanup_symbol_name() in scripts/kallsyms.c is also changed to have the same
> filtering pattern so both kernel and kallsyms tool have the same
> expectation on the order of symbols.
Reviewed-by: Zhen Lei <thunder.leizhen@huawei.com>
>
> [1] https://lore.kernel.org/live-patching/20230615170048.2382735-1-song@kernel.org/T/#u
>
> Fixes: 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
> Reported-by: Song Liu <song@kernel.org>
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---
> kernel/kallsyms.c | 5 ++---
> scripts/kallsyms.c | 6 +++---
> 2 files changed, 5 insertions(+), 6 deletions(-)
>
> Changelogs:
> v1 -> v2:
> . add 'Reported-by: Song Liu <song@kernel.org>'
> . also fix in scripts/kallsyms.c.
>
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 77747391f49b..4874508bb950 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -174,11 +174,10 @@ static bool cleanup_symbol_name(char *s)
> * LLVM appends various suffixes for local functions and variables that
> * must be promoted to global scope as part of LTO. This can break
> * hooking of static functions with kprobes. '.' is not a valid
> - * character in an identifier in C. Suffixes observed:
> + * character in an identifier in C. Suffixes only in LLVM LTO observed:
> * - foo.llvm.[0-9a-f]+
> - * - foo.[0-9a-f]+
> */
> - res = strchr(s, '.');
> + res = strstr(s, ".llvm.");
> if (res) {
> *res = '\0';
> return true;
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index 0d2db41177b2..13af6d0ff845 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -346,10 +346,10 @@ static void cleanup_symbol_name(char *s)
> * ASCII[_] = 5f
> * ASCII[a-z] = 61,7a
> *
> - * As above, replacing '.' with '\0' does not affect the main sorting,
> - * but it helps us with subsorting.
> + * As above, replacing the first '.' in ".llvm." with '\0' does not
> + * affect the main sorting, but it helps us with subsorting.
> */
> - p = strchr(s, '.');
> + p = strstr(s, ".llvm.");
> if (p)
> *p = '\0';
> }
>
--
Regards,
Zhen Lei
On Wed, Jun 28, 2023 at 11:19 AM Yonghong Song <yhs@fb.com> wrote:
>
> Commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
> stripped all function/variable suffixes started with '.' regardless
> of whether those suffixes are generated at LTO mode or not. In fact,
> as far as I know, in LTO mode, when a static function/variable is
> promoted to the global scope, '.llvm.<...>' suffix is added.
>
> The existing mechanism breaks live patch for a LTO kernel even if
> no <symbol>.llvm.<...> symbols are involved. For example, for the following
> kernel symbols:
> $ grep bpf_verifier_vlog /proc/kallsyms
> ffffffff81549f60 t bpf_verifier_vlog
> ffffffff8268b430 d bpf_verifier_vlog._entry
> ffffffff8282a958 d bpf_verifier_vlog._entry_ptr
> ffffffff82e12a1f d bpf_verifier_vlog.__already_done
> 'bpf_verifier_vlog' is a static function. '_entry', '_entry_ptr' and
> '__already_done' are static variables used inside 'bpf_verifier_vlog',
> so llvm promotes them to file-level static with prefix 'bpf_verifier_vlog.'.
> Note that the func-level to file-level static function promotion also
> happens without LTO.
>
> Given a symbol name 'bpf_verifier_vlog', with LTO kernel, current mechanism will
> return 4 symbols to live patch subsystem which current live patching
> subsystem cannot handle it. With non-LTO kernel, only one symbol
> is returned.
>
> In [1], we have a lengthy discussion, the suggestion is to separate two
> cases:
> (1). new symbols with suffix which are generated regardless of whether
> LTO is enabled or not, and
> (2). new symbols with suffix generated only when LTO is enabled.
>
> The cleanup_symbol_name() should only remove suffixes for case (2).
> Case (1) should not be changed so it can work uniformly with or without LTO.
>
> This patch removed LTO-only suffix '.llvm.<...>' so live patching and
> tracing should work the same way for non-LTO kernel.
> The cleanup_symbol_name() in scripts/kallsyms.c is also changed to have the same
> filtering pattern so both kernel and kallsyms tool have the same
> expectation on the order of symbols.
>
> [1] https://lore.kernel.org/live-patching/20230615170048.2382735-1-song@kernel.org/T/#u
>
> Fixes: 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
> Reported-by: Song Liu <song@kernel.org>
> Signed-off-by: Yonghong Song <yhs@fb.com>
Thanks for the patch and improving live patch with LTO. Looking back
at the internal report that resulted in
commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
your version was what I originally had. I did not leave a comment as
to why I changed it when I sent it 2 years ago, and no longer recall
the reason.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
> kernel/kallsyms.c | 5 ++---
> scripts/kallsyms.c | 6 +++---
> 2 files changed, 5 insertions(+), 6 deletions(-)
>
> Changelogs:
> v1 -> v2:
> . add 'Reported-by: Song Liu <song@kernel.org>'
> . also fix in scripts/kallsyms.c.
>
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 77747391f49b..4874508bb950 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -174,11 +174,10 @@ static bool cleanup_symbol_name(char *s)
> * LLVM appends various suffixes for local functions and variables that
> * must be promoted to global scope as part of LTO. This can break
> * hooking of static functions with kprobes. '.' is not a valid
> - * character in an identifier in C. Suffixes observed:
> + * character in an identifier in C. Suffixes only in LLVM LTO observed:
> * - foo.llvm.[0-9a-f]+
> - * - foo.[0-9a-f]+
> */
> - res = strchr(s, '.');
> + res = strstr(s, ".llvm.");
> if (res) {
> *res = '\0';
> return true;
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index 0d2db41177b2..13af6d0ff845 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -346,10 +346,10 @@ static void cleanup_symbol_name(char *s)
> * ASCII[_] = 5f
> * ASCII[a-z] = 61,7a
> *
> - * As above, replacing '.' with '\0' does not affect the main sorting,
> - * but it helps us with subsorting.
> + * As above, replacing the first '.' in ".llvm." with '\0' does not
> + * affect the main sorting, but it helps us with subsorting.
> */
> - p = strchr(s, '.');
> + p = strstr(s, ".llvm.");
> if (p)
> *p = '\0';
> }
> --
> 2.34.1
>
--
Thanks,
~Nick Desaulniers
On 7/7/23 3:27 PM, Nick Desaulniers wrote:
> On Wed, Jun 28, 2023 at 11:19 AM Yonghong Song <yhs@fb.com> wrote:
>>
>> Commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
>> stripped all function/variable suffixes started with '.' regardless
>> of whether those suffixes are generated at LTO mode or not. In fact,
>> as far as I know, in LTO mode, when a static function/variable is
>> promoted to the global scope, '.llvm.<...>' suffix is added.
>>
>> The existing mechanism breaks live patch for a LTO kernel even if
>> no <symbol>.llvm.<...> symbols are involved. For example, for the following
>> kernel symbols:
>> $ grep bpf_verifier_vlog /proc/kallsyms
>> ffffffff81549f60 t bpf_verifier_vlog
>> ffffffff8268b430 d bpf_verifier_vlog._entry
>> ffffffff8282a958 d bpf_verifier_vlog._entry_ptr
>> ffffffff82e12a1f d bpf_verifier_vlog.__already_done
>> 'bpf_verifier_vlog' is a static function. '_entry', '_entry_ptr' and
>> '__already_done' are static variables used inside 'bpf_verifier_vlog',
>> so llvm promotes them to file-level static with prefix 'bpf_verifier_vlog.'.
>> Note that the func-level to file-level static function promotion also
>> happens without LTO.
>>
>> Given a symbol name 'bpf_verifier_vlog', with LTO kernel, current mechanism will
>> return 4 symbols to live patch subsystem which current live patching
>> subsystem cannot handle it. With non-LTO kernel, only one symbol
>> is returned.
>>
>> In [1], we have a lengthy discussion, the suggestion is to separate two
>> cases:
>> (1). new symbols with suffix which are generated regardless of whether
>> LTO is enabled or not, and
>> (2). new symbols with suffix generated only when LTO is enabled.
>>
>> The cleanup_symbol_name() should only remove suffixes for case (2).
>> Case (1) should not be changed so it can work uniformly with or without LTO.
>>
>> This patch removed LTO-only suffix '.llvm.<...>' so live patching and
>> tracing should work the same way for non-LTO kernel.
>> The cleanup_symbol_name() in scripts/kallsyms.c is also changed to have the same
>> filtering pattern so both kernel and kallsyms tool have the same
>> expectation on the order of symbols.
>>
>> [1] https://lore.kernel.org/live-patching/20230615170048.2382735-1-song@kernel.org/T/#u
>>
>> Fixes: 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
>> Reported-by: Song Liu <song@kernel.org>
>> Signed-off-by: Yonghong Song <yhs@fb.com>
>
> Thanks for the patch and improving live patch with LTO. Looking back
> at the internal report that resulted in
> commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
> your version was what I originally had. I did not leave a comment as
> to why I changed it when I sent it 2 years ago, and no longer recall
> the reason.
>
>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Nick, thanks for the review. I am not sure how this patch could
be merged into the mainline. I checked your patch
6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
and it looks like the patch was merged by Kees Cook.
I added Kees in the 'To' list. Kees, could you help merge
this patch if you are okay with the change?
Thanks!
Yonghong
>
>> ---
>> kernel/kallsyms.c | 5 ++---
>> scripts/kallsyms.c | 6 +++---
>> 2 files changed, 5 insertions(+), 6 deletions(-)
>>
>> Changelogs:
>> v1 -> v2:
>> . add 'Reported-by: Song Liu <song@kernel.org>'
>> . also fix in scripts/kallsyms.c.
>>
>> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
>> index 77747391f49b..4874508bb950 100644
>> --- a/kernel/kallsyms.c
>> +++ b/kernel/kallsyms.c
>> @@ -174,11 +174,10 @@ static bool cleanup_symbol_name(char *s)
>> * LLVM appends various suffixes for local functions and variables that
>> * must be promoted to global scope as part of LTO. This can break
>> * hooking of static functions with kprobes. '.' is not a valid
>> - * character in an identifier in C. Suffixes observed:
>> + * character in an identifier in C. Suffixes only in LLVM LTO observed:
>> * - foo.llvm.[0-9a-f]+
>> - * - foo.[0-9a-f]+
>> */
>> - res = strchr(s, '.');
>> + res = strstr(s, ".llvm.");
>> if (res) {
>> *res = '\0';
>> return true;
>> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
>> index 0d2db41177b2..13af6d0ff845 100644
>> --- a/scripts/kallsyms.c
>> +++ b/scripts/kallsyms.c
>> @@ -346,10 +346,10 @@ static void cleanup_symbol_name(char *s)
>> * ASCII[_] = 5f
>> * ASCII[a-z] = 61,7a
>> *
>> - * As above, replacing '.' with '\0' does not affect the main sorting,
>> - * but it helps us with subsorting.
>> + * As above, replacing the first '.' in ".llvm." with '\0' does not
>> + * affect the main sorting, but it helps us with subsorting.
>> */
>> - p = strchr(s, '.');
>> + p = strstr(s, ".llvm.");
>> if (p)
>> *p = '\0';
>> }
>> --
>> 2.34.1
>>
>
>
On 7/7/23 5:23 PM, Yonghong Song wrote:
>
>
> On 7/7/23 3:27 PM, Nick Desaulniers wrote:
>> On Wed, Jun 28, 2023 at 11:19 AM Yonghong Song <yhs@fb.com> wrote:
>>>
>>> Commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static
>>> functions")
>>> stripped all function/variable suffixes started with '.' regardless
>>> of whether those suffixes are generated at LTO mode or not. In fact,
>>> as far as I know, in LTO mode, when a static function/variable is
>>> promoted to the global scope, '.llvm.<...>' suffix is added.
>>>
>>> The existing mechanism breaks live patch for a LTO kernel even if
>>> no <symbol>.llvm.<...> symbols are involved. For example, for the
>>> following
>>> kernel symbols:
>>> $ grep bpf_verifier_vlog /proc/kallsyms
>>> ffffffff81549f60 t bpf_verifier_vlog
>>> ffffffff8268b430 d bpf_verifier_vlog._entry
>>> ffffffff8282a958 d bpf_verifier_vlog._entry_ptr
>>> ffffffff82e12a1f d bpf_verifier_vlog.__already_done
>>> 'bpf_verifier_vlog' is a static function. '_entry', '_entry_ptr' and
>>> '__already_done' are static variables used inside 'bpf_verifier_vlog',
>>> so llvm promotes them to file-level static with prefix
>>> 'bpf_verifier_vlog.'.
>>> Note that the func-level to file-level static function promotion also
>>> happens without LTO.
>>>
>>> Given a symbol name 'bpf_verifier_vlog', with LTO kernel, current
>>> mechanism will
>>> return 4 symbols to live patch subsystem which current live patching
>>> subsystem cannot handle it. With non-LTO kernel, only one symbol
>>> is returned.
>>>
>>> In [1], we have a lengthy discussion, the suggestion is to separate two
>>> cases:
>>> (1). new symbols with suffix which are generated regardless of
>>> whether
>>> LTO is enabled or not, and
>>> (2). new symbols with suffix generated only when LTO is enabled.
>>>
>>> The cleanup_symbol_name() should only remove suffixes for case (2).
>>> Case (1) should not be changed so it can work uniformly with or
>>> without LTO.
>>>
>>> This patch removed LTO-only suffix '.llvm.<...>' so live patching and
>>> tracing should work the same way for non-LTO kernel.
>>> The cleanup_symbol_name() in scripts/kallsyms.c is also changed to
>>> have the same
>>> filtering pattern so both kernel and kallsyms tool have the same
>>> expectation on the order of symbols.
>>>
>>> [1]
>>> https://lore.kernel.org/live-patching/20230615170048.2382735-1-song@kernel.org/T/#u
>>>
>>> Fixes: 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static
>>> functions")
>>> Reported-by: Song Liu <song@kernel.org>
>>> Signed-off-by: Yonghong Song <yhs@fb.com>
>>
>> Thanks for the patch and improving live patch with LTO. Looking back
>> at the internal report that resulted in
>> commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static
>> functions")
>> your version was what I originally had. I did not leave a comment as
>> to why I changed it when I sent it 2 years ago, and no longer recall
>> the reason.
>>
>>
>> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>
> Nick, thanks for the review. I am not sure how this patch could
> be merged into the mainline. I checked your patch
> 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
> and it looks like the patch was merged by Kees Cook.
>
> I added Kees in the 'To' list. Kees, could you help merge
> this patch if you are okay with the change?
Looks like Kees might be on vacation. Nick, Petr, do you
have any suggestions who could take this patch? Thanks!
>
> Thanks!
>
> Yonghong
>
>>
>>> ---
>>> kernel/kallsyms.c | 5 ++---
>>> scripts/kallsyms.c | 6 +++---
>>> 2 files changed, 5 insertions(+), 6 deletions(-)
>>>
>>> Changelogs:
>>> v1 -> v2:
>>> . add 'Reported-by: Song Liu <song@kernel.org>'
>>> . also fix in scripts/kallsyms.c.
>>>
>>> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
>>> index 77747391f49b..4874508bb950 100644
>>> --- a/kernel/kallsyms.c
>>> +++ b/kernel/kallsyms.c
>>> @@ -174,11 +174,10 @@ static bool cleanup_symbol_name(char *s)
>>> * LLVM appends various suffixes for local functions and
>>> variables that
>>> * must be promoted to global scope as part of LTO. This
>>> can break
>>> * hooking of static functions with kprobes. '.' is not a valid
>>> - * character in an identifier in C. Suffixes observed:
>>> + * character in an identifier in C. Suffixes only in LLVM LTO
>>> observed:
>>> * - foo.llvm.[0-9a-f]+
>>> - * - foo.[0-9a-f]+
>>> */
>>> - res = strchr(s, '.');
>>> + res = strstr(s, ".llvm.");
>>> if (res) {
>>> *res = '\0';
>>> return true;
>>> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
>>> index 0d2db41177b2..13af6d0ff845 100644
>>> --- a/scripts/kallsyms.c
>>> +++ b/scripts/kallsyms.c
>>> @@ -346,10 +346,10 @@ static void cleanup_symbol_name(char *s)
>>> * ASCII[_] = 5f
>>> * ASCII[a-z] = 61,7a
>>> *
>>> - * As above, replacing '.' with '\0' does not affect the main
>>> sorting,
>>> - * but it helps us with subsorting.
>>> + * As above, replacing the first '.' in ".llvm." with '\0'
>>> does not
>>> + * affect the main sorting, but it helps us with subsorting.
>>> */
>>> - p = strchr(s, '.');
>>> + p = strstr(s, ".llvm.");
>>> if (p)
>>> *p = '\0';
>>> }
>>> --
>>> 2.34.1
>>>
>>
>>
On Thu, Jun 29, 2023 at 2:19 AM Yonghong Song <yhs@fb.com> wrote:
>
> Commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
> stripped all function/variable suffixes started with '.' regardless
> of whether those suffixes are generated at LTO mode or not. In fact,
> as far as I know, in LTO mode, when a static function/variable is
> promoted to the global scope, '.llvm.<...>' suffix is added.
>
> The existing mechanism breaks live patch for a LTO kernel even if
> no <symbol>.llvm.<...> symbols are involved. For example, for the following
> kernel symbols:
> $ grep bpf_verifier_vlog /proc/kallsyms
> ffffffff81549f60 t bpf_verifier_vlog
> ffffffff8268b430 d bpf_verifier_vlog._entry
> ffffffff8282a958 d bpf_verifier_vlog._entry_ptr
> ffffffff82e12a1f d bpf_verifier_vlog.__already_done
> 'bpf_verifier_vlog' is a static function. '_entry', '_entry_ptr' and
> '__already_done' are static variables used inside 'bpf_verifier_vlog',
> so llvm promotes them to file-level static with prefix 'bpf_verifier_vlog.'.
> Note that the func-level to file-level static function promotion also
> happens without LTO.
>
> Given a symbol name 'bpf_verifier_vlog', with LTO kernel, current mechanism will
> return 4 symbols to live patch subsystem which current live patching
> subsystem cannot handle it. With non-LTO kernel, only one symbol
> is returned.
>
> In [1], we have a lengthy discussion, the suggestion is to separate two
> cases:
> (1). new symbols with suffix which are generated regardless of whether
> LTO is enabled or not, and
> (2). new symbols with suffix generated only when LTO is enabled.
>
> The cleanup_symbol_name() should only remove suffixes for case (2).
> Case (1) should not be changed so it can work uniformly with or without LTO.
>
> This patch removed LTO-only suffix '.llvm.<...>' so live patching and
> tracing should work the same way for non-LTO kernel.
> The cleanup_symbol_name() in scripts/kallsyms.c is also changed to have the same
> filtering pattern so both kernel and kallsyms tool have the same
> expectation on the order of symbols.
>
> [1] https://lore.kernel.org/live-patching/20230615170048.2382735-1-song@kernel.org/T/#u
>
> Fixes: 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
> Reported-by: Song Liu <song@kernel.org>
> Signed-off-by: Yonghong Song <yhs@fb.com>
Acked-by: Song Liu <song@kernel.org>
> ---
> kernel/kallsyms.c | 5 ++---
> scripts/kallsyms.c | 6 +++---
> 2 files changed, 5 insertions(+), 6 deletions(-)
>
> Changelogs:
> v1 -> v2:
> . add 'Reported-by: Song Liu <song@kernel.org>'
> . also fix in scripts/kallsyms.c.
>
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 77747391f49b..4874508bb950 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -174,11 +174,10 @@ static bool cleanup_symbol_name(char *s)
> * LLVM appends various suffixes for local functions and variables that
> * must be promoted to global scope as part of LTO. This can break
> * hooking of static functions with kprobes. '.' is not a valid
> - * character in an identifier in C. Suffixes observed:
> + * character in an identifier in C. Suffixes only in LLVM LTO observed:
> * - foo.llvm.[0-9a-f]+
> - * - foo.[0-9a-f]+
> */
> - res = strchr(s, '.');
> + res = strstr(s, ".llvm.");
> if (res) {
> *res = '\0';
> return true;
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index 0d2db41177b2..13af6d0ff845 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -346,10 +346,10 @@ static void cleanup_symbol_name(char *s)
> * ASCII[_] = 5f
> * ASCII[a-z] = 61,7a
> *
> - * As above, replacing '.' with '\0' does not affect the main sorting,
> - * but it helps us with subsorting.
> + * As above, replacing the first '.' in ".llvm." with '\0' does not
> + * affect the main sorting, but it helps us with subsorting.
> */
> - p = strchr(s, '.');
> + p = strstr(s, ".llvm.");
> if (p)
> *p = '\0';
> }
> --
> 2.34.1
>
On Wed, 28 Jun 2023 11:19:26 -0700, Yonghong Song wrote:
> Commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
> stripped all function/variable suffixes started with '.' regardless
> of whether those suffixes are generated at LTO mode or not. In fact,
> as far as I know, in LTO mode, when a static function/variable is
> promoted to the global scope, '.llvm.<...>' suffix is added.
>
> The existing mechanism breaks live patch for a LTO kernel even if
> no <symbol>.llvm.<...> symbols are involved. For example, for the following
> kernel symbols:
> $ grep bpf_verifier_vlog /proc/kallsyms
> ffffffff81549f60 t bpf_verifier_vlog
> ffffffff8268b430 d bpf_verifier_vlog._entry
> ffffffff8282a958 d bpf_verifier_vlog._entry_ptr
> ffffffff82e12a1f d bpf_verifier_vlog.__already_done
> 'bpf_verifier_vlog' is a static function. '_entry', '_entry_ptr' and
> '__already_done' are static variables used inside 'bpf_verifier_vlog',
> so llvm promotes them to file-level static with prefix 'bpf_verifier_vlog.'.
> Note that the func-level to file-level static function promotion also
> happens without LTO.
>
> [...]
Applied, thanks!
[1/1] kallsyms: strip LTO-only suffixes from promoted global functions
https://git.kernel.org/kees/c/8cc32a9bbf29
Best regards,
--
Kees Cook
On 7/12/23 3:40 PM, Kees Cook wrote:
>
> On Wed, 28 Jun 2023 11:19:26 -0700, Yonghong Song wrote:
>> Commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions")
>> stripped all function/variable suffixes started with '.' regardless
>> of whether those suffixes are generated at LTO mode or not. In fact,
>> as far as I know, in LTO mode, when a static function/variable is
>> promoted to the global scope, '.llvm.<...>' suffix is added.
>>
>> The existing mechanism breaks live patch for a LTO kernel even if
>> no <symbol>.llvm.<...> symbols are involved. For example, for the following
>> kernel symbols:
>> $ grep bpf_verifier_vlog /proc/kallsyms
>> ffffffff81549f60 t bpf_verifier_vlog
>> ffffffff8268b430 d bpf_verifier_vlog._entry
>> ffffffff8282a958 d bpf_verifier_vlog._entry_ptr
>> ffffffff82e12a1f d bpf_verifier_vlog.__already_done
>> 'bpf_verifier_vlog' is a static function. '_entry', '_entry_ptr' and
>> '__already_done' are static variables used inside 'bpf_verifier_vlog',
>> so llvm promotes them to file-level static with prefix 'bpf_verifier_vlog.'.
>> Note that the func-level to file-level static function promotion also
>> happens without LTO.
>>
>> [...]
>
> Applied, thanks!
>
> [1/1] kallsyms: strip LTO-only suffixes from promoted global functions
> https://git.kernel.org/kees/c/8cc32a9bbf29
Thanks Kees!
>
> Best regards,
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