[PATCH] libbpf: Support raw btf placed in the default path

[PATCH] libbpf: Support raw btf placed in the default path

[chentao.ct]

Now only elf btf can be placed in the default path, raw btf should
also can be there.

Signed-off-by: chentao.ct <chentao.kernel@linux.alibaba.com>
---
 tools/lib/bpf/btf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index bb1e06e..b22b5b3 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -4661,7 +4661,7 @@ struct btf *btf__load_vmlinux_btf(void)
 	} locations[] = {
 		/* try canonical vmlinux BTF through sysfs first */
 		{ "/sys/kernel/btf/vmlinux", true /* raw BTF */ },
-		/* fall back to trying to find vmlinux ELF on disk otherwise */
+		/* fall back to trying to find vmlinux RAW/ELF on disk otherwise */
 		{ "/boot/vmlinux-%1$s" },
 		{ "/lib/modules/%1$s/vmlinux-%1$s" },
 		{ "/lib/modules/%1$s/build/vmlinux" },
@@ -4686,7 +4686,7 @@ struct btf *btf__load_vmlinux_btf(void)
 		if (locations[i].raw_btf)
 			btf = btf__parse_raw(path);
 		else
-			btf = btf__parse_elf(path, NULL);
+			btf = btf__parse(path, NULL);
 		err = libbpf_get_error(btf);
 		pr_debug("loading kernel BTF '%s': %d\n", path, err);
 		if (err)
-- 
2.2.1

Re: [PATCH] libbpf: Support raw btf placed in the default path

[Andrii Nakryiko]

On Wed, Aug 24, 2022 at 7:05 AM chentao.ct
<chentao.kernel@linux.alibaba.com> wrote:
>
> Now only elf btf can be placed in the default path, raw btf should
> also can be there.
>

It's not clear what you are trying to achieve. Do you want libbpf to
attempt to load /boot/vmlinux-%1$s as raw BTF as well (so you can sort
of sneak in pregenerated BTF), or what exactly?
btf__load_vmlinux_btf() code already supports loading raw BTF, it just
needs to be explicitly specified in locations table.

So with your change locations[i].raw_btf check doesn't make sense and
we need to clean this up.

But first, let's discuss the use case, instead of your specific solution.


> Signed-off-by: chentao.ct <chentao.kernel@linux.alibaba.com>
> ---
>  tools/lib/bpf/btf.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index bb1e06e..b22b5b3 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -4661,7 +4661,7 @@ struct btf *btf__load_vmlinux_btf(void)
>         } locations[] = {
>                 /* try canonical vmlinux BTF through sysfs first */
>                 { "/sys/kernel/btf/vmlinux", true /* raw BTF */ },
> -               /* fall back to trying to find vmlinux ELF on disk otherwise */
> +               /* fall back to trying to find vmlinux RAW/ELF on disk otherwise */
>                 { "/boot/vmlinux-%1$s" },
>                 { "/lib/modules/%1$s/vmlinux-%1$s" },
>                 { "/lib/modules/%1$s/build/vmlinux" },
> @@ -4686,7 +4686,7 @@ struct btf *btf__load_vmlinux_btf(void)
>                 if (locations[i].raw_btf)
>                         btf = btf__parse_raw(path);
>                 else
> -                       btf = btf__parse_elf(path, NULL);
> +                       btf = btf__parse(path, NULL);
>                 err = libbpf_get_error(btf);
>                 pr_debug("loading kernel BTF '%s': %d\n", path, err);
>                 if (err)
> --
> 2.2.1
>

Re: [PATCH] libbpf: Support raw btf placed in the default path

[Tao Chen]

Hi Nakryiko, thank you for your reply. Yes, i happed to put the raw
BTF made by myself in /boot on kernel4.19, unluckly it reported error.
So is it possible to allow the raw BTF in /boot directly, athough we
can set the specified btf location again to solve the problem with the
bpf_object_open_opts interface. 


As you say, maybe we can remove the locations[i].raw_btf check, just
use the btf__parse. It looks more concise.


在 2022/8/26 上午4:26, Andrii Nakryiko 写道:
> On Wed, Aug 24, 2022 at 7:05 AM chentao.ct
> <chentao.kernel@linux.alibaba.com> wrote:
>>
>> Now only elf btf can be placed in the default path, raw btf should
>> also can be there.
>>
> 
> It's not clear what you are trying to achieve. Do you want libbpf to
> attempt to load /boot/vmlinux-%1$s as raw BTF as well (so you can sort
> of sneak in pregenerated BTF), or what exactly?
> btf__load_vmlinux_btf() code already supports loading raw BTF, it just
> needs to be explicitly specified in locations table.
> 
> So with your change locations[i].raw_btf check doesn't make sense and
> we need to clean this up.
> 
> But first, let's discuss the use case, instead of your specific solution.
> 
> 
>> Signed-off-by: chentao.ct <chentao.kernel@linux.alibaba.com>
>> ---
>>   tools/lib/bpf/btf.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
>> index bb1e06e..b22b5b3 100644
>> --- a/tools/lib/bpf/btf.c
>> +++ b/tools/lib/bpf/btf.c
>> @@ -4661,7 +4661,7 @@ struct btf *btf__load_vmlinux_btf(void)
>>          } locations[] = {
>>                  /* try canonical vmlinux BTF through sysfs first */
>>                  { "/sys/kernel/btf/vmlinux", true /* raw BTF */ },
>> -               /* fall back to trying to find vmlinux ELF on disk otherwise */
>> +               /* fall back to trying to find vmlinux RAW/ELF on disk otherwise */
>>                  { "/boot/vmlinux-%1$s" },
>>                  { "/lib/modules/%1$s/vmlinux-%1$s" },
>>                  { "/lib/modules/%1$s/build/vmlinux" },
>> @@ -4686,7 +4686,7 @@ struct btf *btf__load_vmlinux_btf(void)
>>                  if (locations[i].raw_btf)
>>                          btf = btf__parse_raw(path);
>>                  else
>> -                       btf = btf__parse_elf(path, NULL);
>> +                       btf = btf__parse(path, NULL);
>>                  err = libbpf_get_error(btf);
>>                  pr_debug("loading kernel BTF '%s': %d\n", path, err);
>>                  if (err)
>> --
>> 2.2.1
>>

Re: [PATCH] libbpf: Support raw btf placed in the default path

[Andrii Nakryiko]

On Sun, Aug 28, 2022 at 10:36 PM Tao Chen
<chentao.kernel@linux.alibaba.com> wrote:
>
> Hi Nakryiko, thank you for your reply. Yes, i happed to put the raw
> BTF made by myself in /boot on kernel4.19, unluckly it reported error.
> So is it possible to allow the raw BTF in /boot directly, athough we
> can set the specified btf location again to solve the problem with the
> bpf_object_open_opts interface.
>
> As you say, maybe we can remove the locations[i].raw_btf check, just
> use the btf__parse, It looks more concise.

Please don't top post, reply inline (that's kernel mail lists rules).

But yes, I think we can just use btf__parse and let libbpf figure out.
Please send a patch.

>
> 在 2022/8/26 上午4:26, Andrii Nakryiko 写道:
>
> On Wed, Aug 24, 2022 at 7:05 AM chentao.ct
> <chentao.kernel@linux.alibaba.com> wrote:
>
> Now only elf btf can be placed in the default path, raw btf should
> also can be there.
>
> It's not clear what you are trying to achieve. Do you want libbpf to
> attempt to load /boot/vmlinux-%1$s as raw BTF as well (so you can sort
> of sneak in pregenerated BTF), or what exactly?
> btf__load_vmlinux_btf() code already supports loading raw BTF, it just
> needs to be explicitly specified in locations table.
>
> So with your change locations[i].raw_btf check doesn't make sense and
> we need to clean this up.
>
> But first, let's discuss the use case, instead of your specific solution.
>
>
> Signed-off-by: chentao.ct <chentao.kernel@linux.alibaba.com>
> ---
>  tools/lib/bpf/btf.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index bb1e06e..b22b5b3 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -4661,7 +4661,7 @@ struct btf *btf__load_vmlinux_btf(void)
>         } locations[] = {
>                 /* try canonical vmlinux BTF through sysfs first */
>                 { "/sys/kernel/btf/vmlinux", true /* raw BTF */ },
> -               /* fall back to trying to find vmlinux ELF on disk otherwise */
> +               /* fall back to trying to find vmlinux RAW/ELF on disk otherwise */
>                 { "/boot/vmlinux-%1$s" },
>                 { "/lib/modules/%1$s/vmlinux-%1$s" },
>                 { "/lib/modules/%1$s/build/vmlinux" },
> @@ -4686,7 +4686,7 @@ struct btf *btf__load_vmlinux_btf(void)
>                 if (locations[i].raw_btf)
>                         btf = btf__parse_raw(path);
>                 else
> -                       btf = btf__parse_elf(path, NULL);
> +                       btf = btf__parse(path, NULL);
>                 err = libbpf_get_error(btf);
>                 pr_debug("loading kernel BTF '%s': %d\n", path, err);
>                 if (err)
> --
> 2.2.1
>

Re: [PATCH] libbpf: Support raw btf placed in the default path

[Tao Chen]

在 2022/9/10 上午3:00, Andrii Nakryiko 写道:
> On Sun, Aug 28, 2022 at 10:36 PM Tao Chen
> <chentao.kernel@linux.alibaba.com> wrote:
>>
>> Hi Nakryiko, thank you for your reply. Yes, i happed to put the raw
>> BTF made by myself in /boot on kernel4.19, unluckly it reported error.
>> So is it possible to allow the raw BTF in /boot directly, athough we
>> can set the specified btf location again to solve the problem with the
>> bpf_object_open_opts interface.
>>
>> As you say, maybe we can remove the locations[i].raw_btf check, just
>> use the btf__parse, It looks more concise.
> 
> Please don't top post, reply inline (that's kernel mail lists rules).
> 
> But yes, I think we can just use btf__parse and let libbpf figure out.
> Please send a patch.
> 

Thank you, i will send the patch in v2.
>>
>> 在 2022/8/26 上午4:26, Andrii Nakryiko 写道:
>>
>> On Wed, Aug 24, 2022 at 7:05 AM chentao.ct
>> <chentao.kernel@linux.alibaba.com> wrote:
>>
>> Now only elf btf can be placed in the default path, raw btf should
>> also can be there.
>>
>> It's not clear what you are trying to achieve. Do you want libbpf to
>> attempt to load /boot/vmlinux-%1$s as raw BTF as well (so you can sort
>> of sneak in pregenerated BTF), or what exactly?
>> btf__load_vmlinux_btf() code already supports loading raw BTF, it just
>> needs to be explicitly specified in locations table.
>>
>> So with your change locations[i].raw_btf check doesn't make sense and
>> we need to clean this up.
>>
>> But first, let's discuss the use case, instead of your specific solution.
>>
>>
>> Signed-off-by: chentao.ct <chentao.kernel@linux.alibaba.com>
>> ---
>>   tools/lib/bpf/btf.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
>> index bb1e06e..b22b5b3 100644
>> --- a/tools/lib/bpf/btf.c
>> +++ b/tools/lib/bpf/btf.c
>> @@ -4661,7 +4661,7 @@ struct btf *btf__load_vmlinux_btf(void)
>>          } locations[] = {
>>                  /* try canonical vmlinux BTF through sysfs first */
>>                  { "/sys/kernel/btf/vmlinux", true /* raw BTF */ },
>> -               /* fall back to trying to find vmlinux ELF on disk otherwise */
>> +               /* fall back to trying to find vmlinux RAW/ELF on disk otherwise */
>>                  { "/boot/vmlinux-%1$s" },
>>                  { "/lib/modules/%1$s/vmlinux-%1$s" },
>>                  { "/lib/modules/%1$s/build/vmlinux" },
>> @@ -4686,7 +4686,7 @@ struct btf *btf__load_vmlinux_btf(void)
>>                  if (locations[i].raw_btf)
>>                          btf = btf__parse_raw(path);
>>                  else
>> -                       btf = btf__parse_elf(path, NULL);
>> +                       btf = btf__parse(path, NULL);
>>                  err = libbpf_get_error(btf);
>>                  pr_debug("loading kernel BTF '%s': %d\n", path, err);
>>                  if (err)
>> --
>> 2.2.1
>>