[PATCH] bpftool: Try to read btf as raw data if elf read fails

[PATCH] bpftool: Try to read btf as raw data if elf read fails

[Jiri Olsa]

The bpftool interface stays the same, but now it's possible
to run it over BTF raw data, like:

  $ bpftool btf dump file /sys/kernel/btf/vmlinux
  libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux
  [1] INT '(anon)' size=4 bits_offset=0 nr_bits=32 encoding=(none)
  [2] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
  [3] CONST '(anon)' type_id=2

I'm also adding err init to 0 because I was getting uninitialized
warnings from gcc.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/bpf/bpftool/btf.c | 47 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 42 insertions(+), 5 deletions(-)

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index 9a9376d1d3df..100fb7e02329 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -12,6 +12,9 @@
 #include <libbpf.h>
 #include <linux/btf.h>
 #include <linux/hashtable.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
 
 #include "btf.h"
 #include "json_writer.h"
@@ -388,6 +391,35 @@ static int dump_btf_c(const struct btf *btf,
 	return err;
 }
 
+static struct btf *btf__parse_raw(const char *file)
+{
+	struct btf *btf = ERR_PTR(-EINVAL);
+	__u8 *buf = NULL;
+	struct stat st;
+	FILE *f;
+
+	if (stat(file, &st))
+		return btf;
+
+	f = fopen(file, "rb");
+	if (!f)
+		return btf;
+
+	buf = malloc(st.st_size);
+	if (!buf)
+		goto err;
+
+	if ((size_t) st.st_size != fread(buf, 1, st.st_size, f))
+		goto err;
+
+	btf = btf__new(buf, st.st_size);
+
+err:
+	free(buf);
+	fclose(f);
+	return btf;
+}
+
 static int do_dump(int argc, char **argv)
 {
 	struct btf *btf = NULL;
@@ -397,7 +429,7 @@ static int do_dump(int argc, char **argv)
 	__u32 btf_id = -1;
 	const char *src;
 	int fd = -1;
-	int err;
+	int err = 0;
 
 	if (!REQ_ARGS(2)) {
 		usage();
@@ -468,10 +500,15 @@ static int do_dump(int argc, char **argv)
 		btf = btf__parse_elf(*argv, NULL);
 		if (IS_ERR(btf)) {
 			err = PTR_ERR(btf);
-			btf = NULL;
-			p_err("failed to load BTF from %s: %s", 
-			      *argv, strerror(err));
-			goto done;
+			if (err == -LIBBPF_ERRNO__FORMAT)
+				btf = btf__parse_raw(*argv);
+			if (IS_ERR(btf)) {
+				btf = NULL;
+				/* Display the original error value. */
+				p_err("failed to load BTF from %s: %s",
+				      *argv, strerror(err));
+				goto done;
+			}
 		}
 		NEXT_ARG();
 	} else {
-- 
2.21.0

Re: [PATCH] bpftool: Try to read btf as raw data if elf read fails

[Andrii Nakryiko]

On 10/18/19 3:34 AM, Jiri Olsa wrote:
> The bpftool interface stays the same, but now it's possible
> to run it over BTF raw data, like:

Oh, great, I had similar patch laying around for a while, never got to 
cleaning it up, though, so thanks for picking this up!

> 
>    $ bpftool btf dump file /sys/kernel/btf/vmlinux
>    libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux

We should implement this so that we don't get an extra log output with 
errors. I've been thinking about checking first few bytes of the file. 
If that matches BTF_MAGIC, then try to parse it as raw BTF, otherwise 
parse as ELF w/ BTF. Does it make sense?

>    [1] INT '(anon)' size=4 bits_offset=0 nr_bits=32 encoding=(none)
>    [2] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
>    [3] CONST '(anon)' type_id=2
> 
> I'm also adding err init to 0 because I was getting uninitialized
> warnings from gcc.
> 
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>   tools/bpf/bpftool/btf.c | 47 ++++++++++++++++++++++++++++++++++++-----
>   1 file changed, 42 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> index 9a9376d1d3df..100fb7e02329 100644
> --- a/tools/bpf/bpftool/btf.c
> +++ b/tools/bpf/bpftool/btf.c
> @@ -12,6 +12,9 @@
>   #include <libbpf.h>
>   #include <linux/btf.h>
>   #include <linux/hashtable.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <unistd.h>
>   
>   #include "btf.h"
>   #include "json_writer.h"
> @@ -388,6 +391,35 @@ static int dump_btf_c(const struct btf *btf,
>   	return err;
>   }
>   
> +static struct btf *btf__parse_raw(const char *file)
> +{
> +	struct btf *btf = ERR_PTR(-EINVAL);
> +	__u8 *buf = NULL;
> +	struct stat st;
> +	FILE *f;
> +
> +	if (stat(file, &st))
> +		return btf;
> +
> +	f = fopen(file, "rb");
> +	if (!f)
> +		return btf;
> +
> +	buf = malloc(st.st_size);
> +	if (!buf)
> +		goto err;
> +
> +	if ((size_t) st.st_size != fread(buf, 1, st.st_size, f))
> +		goto err;
> +
> +	btf = btf__new(buf, st.st_size);
> +
> +err:
> +	free(buf);
> +	fclose(f);
> +	return btf;
> +}
> +
>   static int do_dump(int argc, char **argv)
>   {
>   	struct btf *btf = NULL;
> @@ -397,7 +429,7 @@ static int do_dump(int argc, char **argv)
>   	__u32 btf_id = -1;
>   	const char *src;
>   	int fd = -1;
> -	int err;
> +	int err = 0;
>   
>   	if (!REQ_ARGS(2)) {
>   		usage();
> @@ -468,10 +500,15 @@ static int do_dump(int argc, char **argv)
>   		btf = btf__parse_elf(*argv, NULL);
>   		if (IS_ERR(btf)) {
>   			err = PTR_ERR(btf);
> -			btf = NULL;
> -			p_err("failed to load BTF from %s: %s",
> -			      *argv, strerror(err));
> -			goto done;
> +			if (err == -LIBBPF_ERRNO__FORMAT)
> +				btf = btf__parse_raw(*argv);
> +			if (IS_ERR(btf)) {
> +				btf = NULL;
> +				/* Display the original error value. */
> +				p_err("failed to load BTF from %s: %s",
> +				      *argv, strerror(err));
> +				goto done;
> +			}
>   		}
>   		NEXT_ARG();
>   	} else {
> 

Re: [PATCH] bpftool: Try to read btf as raw data if elf read fails

[Yonghong Song]

On 10/18/19 9:48 AM, Andrii Nakryiko wrote:
> On 10/18/19 3:34 AM, Jiri Olsa wrote:
>> The bpftool interface stays the same, but now it's possible
>> to run it over BTF raw data, like:
> 
> Oh, great, I had similar patch laying around for a while, never got to
> cleaning it up, though, so thanks for picking this up!
> 
>>
>>     $ bpftool btf dump file /sys/kernel/btf/vmlinux
>>     libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux
> 
> We should implement this so that we don't get an extra log output with
> errors. I've been thinking about checking first few bytes of the file.
> If that matches BTF_MAGIC, then try to parse it as raw BTF, otherwise
> parse as ELF w/ BTF. Does it make sense?

Agreed, this makes sense. We should not emit errors in such cases.
One minor comment below.

> 
>>     [1] INT '(anon)' size=4 bits_offset=0 nr_bits=32 encoding=(none)
>>     [2] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
>>     [3] CONST '(anon)' type_id=2
>>
>> I'm also adding err init to 0 because I was getting uninitialized
>> warnings from gcc.
>>
>> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
>> ---
>>    tools/bpf/bpftool/btf.c | 47 ++++++++++++++++++++++++++++++++++++-----
>>    1 file changed, 42 insertions(+), 5 deletions(-)
>>
>> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
>> index 9a9376d1d3df..100fb7e02329 100644
>> --- a/tools/bpf/bpftool/btf.c
>> +++ b/tools/bpf/bpftool/btf.c
>> @@ -12,6 +12,9 @@
>>    #include <libbpf.h>
>>    #include <linux/btf.h>
>>    #include <linux/hashtable.h>
>> +#include <sys/types.h>
>> +#include <sys/stat.h>
>> +#include <unistd.h>
>>    
>>    #include "btf.h"
>>    #include "json_writer.h"
>> @@ -388,6 +391,35 @@ static int dump_btf_c(const struct btf *btf,
>>    	return err;
>>    }
>>    
>> +static struct btf *btf__parse_raw(const char *file)
>> +{
>> +	struct btf *btf = ERR_PTR(-EINVAL);
>> +	__u8 *buf = NULL;
>> +	struct stat st;
>> +	FILE *f;
>> +
>> +	if (stat(file, &st))
>> +		return btf;
>> +
>> +	f = fopen(file, "rb");
>> +	if (!f)
>> +		return btf;
>> +
>> +	buf = malloc(st.st_size);
>> +	if (!buf)
>> +		goto err;
>> +
>> +	if ((size_t) st.st_size != fread(buf, 1, st.st_size, f))
>> +		goto err;
>> +
>> +	btf = btf__new(buf, st.st_size);
>> +
>> +err:

Non error case can also reach here. Let us change
label to a different name, e.g., "done"?

>> +	free(buf);
>> +	fclose(f);
>> +	return btf;
>> +}
>> +
>>    static int do_dump(int argc, char **argv)
>>    {
>>    	struct btf *btf = NULL;
>> @@ -397,7 +429,7 @@ static int do_dump(int argc, char **argv)
>>    	__u32 btf_id = -1;
>>    	const char *src;
>>    	int fd = -1;
>> -	int err;
>> +	int err = 0;
>>    
>>    	if (!REQ_ARGS(2)) {
>>    		usage();
>> @@ -468,10 +500,15 @@ static int do_dump(int argc, char **argv)
>>    		btf = btf__parse_elf(*argv, NULL);
>>    		if (IS_ERR(btf)) {
>>    			err = PTR_ERR(btf);
>> -			btf = NULL;
>> -			p_err("failed to load BTF from %s: %s",
>> -			      *argv, strerror(err));
>> -			goto done;
>> +			if (err == -LIBBPF_ERRNO__FORMAT)
>> +				btf = btf__parse_raw(*argv);
>> +			if (IS_ERR(btf)) {
>> +				btf = NULL;
>> +				/* Display the original error value. */
>> +				p_err("failed to load BTF from %s: %s",
>> +				      *argv, strerror(err));
>> +				goto done;
>> +			}
>>    		}
>>    		NEXT_ARG();
>>    	} else {
>>
> 

Re: [PATCH] bpftool: Try to read btf as raw data if elf read fails

[Jiri Olsa]

On Fri, Oct 18, 2019 at 08:04:44PM +0000, Yonghong Song wrote:

SNIP

> >> +	FILE *f;
> >> +
> >> +	if (stat(file, &st))
> >> +		return btf;
> >> +
> >> +	f = fopen(file, "rb");
> >> +	if (!f)
> >> +		return btf;
> >> +
> >> +	buf = malloc(st.st_size);
> >> +	if (!buf)
> >> +		goto err;
> >> +
> >> +	if ((size_t) st.st_size != fread(buf, 1, st.st_size, f))
> >> +		goto err;
> >> +
> >> +	btf = btf__new(buf, st.st_size);
> >> +
> >> +err:
> 
> Non error case can also reach here. Let us change
> label to a different name, e.g., "done"?

ok, will change

thanks,
jirka

Re: [PATCH] bpftool: Try to read btf as raw data if elf read fails

[Jiri Olsa]

On Fri, Oct 18, 2019 at 04:48:25PM +0000, Andrii Nakryiko wrote:
> On 10/18/19 3:34 AM, Jiri Olsa wrote:
> > The bpftool interface stays the same, but now it's possible
> > to run it over BTF raw data, like:
> 
> Oh, great, I had similar patch laying around for a while, never got to 
> cleaning it up, though, so thanks for picking this up!
> 
> > 
> >    $ bpftool btf dump file /sys/kernel/btf/vmlinux
> >    libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux
> 
> We should implement this so that we don't get an extra log output with 
> errors. I've been thinking about checking first few bytes of the file. 
> If that matches BTF_MAGIC, then try to parse it as raw BTF, otherwise 
> parse as ELF w/ BTF. Does it make sense?

ok, sounds good

jirka

Re: [PATCH] bpftool: Try to read btf as raw data if elf read fails

[Jakub Kicinski]

On Fri, 18 Oct 2019 12:34:04 +0200, Jiri Olsa wrote:
> The bpftool interface stays the same, but now it's possible
> to run it over BTF raw data, like:
> 
>   $ bpftool btf dump file /sys/kernel/btf/vmlinux
>   libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux
>   [1] INT '(anon)' size=4 bits_offset=0 nr_bits=32 encoding=(none)
>   [2] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
>   [3] CONST '(anon)' type_id=2
> 
> I'm also adding err init to 0 because I was getting uninitialized
> warnings from gcc.
> 
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  tools/bpf/bpftool/btf.c | 47 ++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 42 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> index 9a9376d1d3df..100fb7e02329 100644
> --- a/tools/bpf/bpftool/btf.c
> +++ b/tools/bpf/bpftool/btf.c
> @@ -12,6 +12,9 @@
>  #include <libbpf.h>
>  #include <linux/btf.h>
>  #include <linux/hashtable.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <unistd.h>
>  
>  #include "btf.h"
>  #include "json_writer.h"
> @@ -388,6 +391,35 @@ static int dump_btf_c(const struct btf *btf,
>  	return err;
>  }
>  
> +static struct btf *btf__parse_raw(const char *file)
> +{
> +	struct btf *btf = ERR_PTR(-EINVAL);
> +	__u8 *buf = NULL;

Please drop the inits

> +	struct stat st;
> +	FILE *f;
> +
> +	if (stat(file, &st))
> +		return btf;

And return constants here

> +	f = fopen(file, "rb");
> +	if (!f)
> +		return btf;

and here

> +	buf = malloc(st.st_size);
> +	if (!buf)
> +		goto err;

and jump to the right place here.

> +	if ((size_t) st.st_size != fread(buf, 1, st.st_size, f))
> +		goto err;
> +
> +	btf = btf__new(buf, st.st_size);
> +
> +err:

The prefix for error labels which is shared with non-error path is exit_

> +	free(buf);
> +	fclose(f);
> +	return btf;
> +}
> +
>  static int do_dump(int argc, char **argv)
>  {
>  	struct btf *btf = NULL;
> @@ -397,7 +429,7 @@ static int do_dump(int argc, char **argv)
>  	__u32 btf_id = -1;
>  	const char *src;
>  	int fd = -1;
> -	int err;
> +	int err = 0;

This change looks unnecessary.

>  	if (!REQ_ARGS(2)) {
>  		usage();
> @@ -468,10 +500,15 @@ static int do_dump(int argc, char **argv)
>  		btf = btf__parse_elf(*argv, NULL);
>  		if (IS_ERR(btf)) {
>  			err = PTR_ERR(btf);
> -			btf = NULL;
> -			p_err("failed to load BTF from %s: %s", 
> -			      *argv, strerror(err));
> -			goto done;
> +			if (err == -LIBBPF_ERRNO__FORMAT)
> +				btf = btf__parse_raw(*argv);
> +			if (IS_ERR(btf)) {
> +				btf = NULL;
> +				/* Display the original error value. */
> +				p_err("failed to load BTF from %s: %s",
> +				      *argv, strerror(err));
> +				goto done;
> +			}
>  		}
>  		NEXT_ARG();
>  	} else {

Re: [PATCH] bpftool: Try to read btf as raw data if elf read fails

[Jiri Olsa]

On Fri, Oct 18, 2019 at 03:39:05PM -0700, Jakub Kicinski wrote:
> On Fri, 18 Oct 2019 12:34:04 +0200, Jiri Olsa wrote:
> > The bpftool interface stays the same, but now it's possible
> > to run it over BTF raw data, like:
> > 
> >   $ bpftool btf dump file /sys/kernel/btf/vmlinux
> >   libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux
> >   [1] INT '(anon)' size=4 bits_offset=0 nr_bits=32 encoding=(none)
> >   [2] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
> >   [3] CONST '(anon)' type_id=2
> > 
> > I'm also adding err init to 0 because I was getting uninitialized
> > warnings from gcc.
> > 
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> >  tools/bpf/bpftool/btf.c | 47 ++++++++++++++++++++++++++++++++++++-----
> >  1 file changed, 42 insertions(+), 5 deletions(-)
> > 
> > diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> > index 9a9376d1d3df..100fb7e02329 100644
> > --- a/tools/bpf/bpftool/btf.c
> > +++ b/tools/bpf/bpftool/btf.c
> > @@ -12,6 +12,9 @@
> >  #include <libbpf.h>
> >  #include <linux/btf.h>
> >  #include <linux/hashtable.h>
> > +#include <sys/types.h>
> > +#include <sys/stat.h>
> > +#include <unistd.h>
> >  
> >  #include "btf.h"
> >  #include "json_writer.h"
> > @@ -388,6 +391,35 @@ static int dump_btf_c(const struct btf *btf,
> >  	return err;
> >  }
> >  
> > +static struct btf *btf__parse_raw(const char *file)
> > +{
> > +	struct btf *btf = ERR_PTR(-EINVAL);
> > +	__u8 *buf = NULL;
> 
> Please drop the inits
> 
> > +	struct stat st;
> > +	FILE *f;
> > +
> > +	if (stat(file, &st))
> > +		return btf;
> 
> And return constants here
> 
> > +	f = fopen(file, "rb");
> > +	if (!f)
> > +		return btf;
> 
> and here
> 
> > +	buf = malloc(st.st_size);
> > +	if (!buf)
> > +		goto err;
> 
> and jump to the right place here.
> 
> > +	if ((size_t) st.st_size != fread(buf, 1, st.st_size, f))
> > +		goto err;
> > +
> > +	btf = btf__new(buf, st.st_size);
> > +
> > +err:
> 
> The prefix for error labels which is shared with non-error path is exit_
> 
> > +	free(buf);
> > +	fclose(f);
> > +	return btf;
> > +}
> > +

ok for all above

> >  static int do_dump(int argc, char **argv)
> >  {
> >  	struct btf *btf = NULL;
> > @@ -397,7 +429,7 @@ static int do_dump(int argc, char **argv)
> >  	__u32 btf_id = -1;
> >  	const char *src;
> >  	int fd = -1;
> > -	int err;
> > +	int err = 0;
> 
> This change looks unnecessary.

I'm getting confusing warnings from gcc about this,
but there is a code path where do_dump would return
untouched err:

  do_dump
     int err;

     } else if (is_prefix(src, "file")) {
       btf = btf__parse_elf(*argv, NULL);   // succeeds

     }

     while (argc) {
       if (is_prefix(*argv, "format")) {
       else {                                // in here
          goto done;
       }

     done:
       return err;

thanks,
jirka

Re: [PATCH] bpftool: Try to read btf as raw data if elf read fails

[Jakub Kicinski]

On Mon, 21 Oct 2019 16:02:27 +0200, Jiri Olsa wrote:
> > >  static int do_dump(int argc, char **argv)
> > >  {
> > >  	struct btf *btf = NULL;
> > > @@ -397,7 +429,7 @@ static int do_dump(int argc, char **argv)
> > >  	__u32 btf_id = -1;
> > >  	const char *src;
> > >  	int fd = -1;
> > > -	int err;
> > > +	int err = 0;  
> > 
> > This change looks unnecessary.  
> 
> I'm getting confusing warnings from gcc about this,
> but there is a code path where do_dump would return
> untouched err:
> 
>   do_dump
>      int err;
> 
>      } else if (is_prefix(src, "file")) {
>        btf = btf__parse_elf(*argv, NULL);   // succeeds
> 
>      }
> 
>      while (argc) {
>        if (is_prefix(*argv, "format")) {
>        else {                                // in here
>           goto done;
>        }
> 
>      done:
>        return err;

ugh, right those look legit, although unrelated to you change.

err should always be set before jumping to 'done'. The error
setting in this function looks super messy :( Sometimes is returns
errno codes, sometimes positive values, sometimes negative, sometimes
just -1. Sometimes it jumps to 'done' for no good reason, ahh :/