Re: [PATCH v3 1/3] perf dso: Use libbfd to read build_id and .gnu_debuglink section

[Jiri Olsa]

On Fri, Aug 21, 2020 at 06:52:36PM +0200, Remi Bernon wrote:
> Wine generates PE binaries for most of its modules and perf is unable
> to parse these files to get build_id or .gnu_debuglink section.
> 
> Using libbfd when available, instead of libelf, makes it possible to
> resolve debug file location regardless of the dso binary format.
> 
> Signed-off-by: Remi Bernon <rbernon@xxxxxxxxxxxxxxx>
> Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Jacek Caban <jacek@xxxxxxxxxxxxxxx>
> ---
> 
> v3: Rebase and small changes to PATCH 2/3 and and PATCH 3/3.

all 3 patches look ok to me especially since I found out the new
code for loading symbols is for non ELF objects only ;-)

it'd be great if somebody with libbfd skills could review this,
but for me it looks ok.. for patchset:

Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>

thanks,
jirka

> 
>  tools/perf/util/symbol-elf.c | 80 ++++++++++++++++++++++++++++++++++--
>  1 file changed, 77 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index 8cc4b0059fb0..f7432c4a4154 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -50,6 +50,10 @@ typedef Elf64_Nhdr GElf_Nhdr;
>  #define DMGL_ANSI        (1 << 1)       /* Include const, volatile, etc */
>  #endif
>  
> +#ifdef HAVE_LIBBFD_SUPPORT
> +#define PACKAGE 'perf'
> +#include <bfd.h>
> +#else
>  #ifdef HAVE_CPLUS_DEMANGLE_SUPPORT
>  extern char *cplus_demangle(const char *, int);
>  
> @@ -65,9 +69,7 @@ static inline char *bfd_demangle(void __maybe_unused *v,
>  {
>  	return NULL;
>  }
> -#else
> -#define PACKAGE 'perf'
> -#include <bfd.h>
> +#endif
>  #endif
>  #endif
>  
> @@ -530,6 +532,36 @@ static int elf_read_build_id(Elf *elf, void *bf, size_t size)
>  	return err;
>  }
>  
> +#ifdef HAVE_LIBBFD_SUPPORT
> +
> +int filename__read_build_id(const char *filename, void *bf, size_t size)
> +{
> +	int err = -1;
> +	bfd *abfd;
> +
> +	abfd = bfd_openr(filename, NULL);
> +	if (!abfd)
> +		return -1;
> +
> +	if (!bfd_check_format(abfd, bfd_object)) {
> +		pr_debug2("%s: cannot read %s bfd file.\n", __func__, filename);
> +		goto out_close;
> +	}
> +
> +	if (!abfd->build_id || abfd->build_id->size > size)
> +		goto out_close;
> +
> +	memcpy(bf, abfd->build_id->data, abfd->build_id->size);
> +	memset(bf + abfd->build_id->size, 0, size - abfd->build_id->size);
> +	err = abfd->build_id->size;
> +
> +out_close:
> +	bfd_close(abfd);
> +	return err;
> +}
> +
> +#else
> +
>  int filename__read_build_id(const char *filename, void *bf, size_t size)
>  {
>  	int fd, err = -1;
> @@ -557,6 +589,8 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
>  	return err;
>  }
>  
> +#endif
> +
>  int sysfs__read_build_id(const char *filename, void *build_id, size_t size)
>  {
>  	int fd, err = -1;
> @@ -608,6 +642,44 @@ int sysfs__read_build_id(const char *filename, void *build_id, size_t size)
>  	return err;
>  }
>  
> +#ifdef HAVE_LIBBFD_SUPPORT
> +
> +int filename__read_debuglink(const char *filename, char *debuglink,
> +			     size_t size)
> +{
> +	int err = -1;
> +	asection *section;
> +	bfd *abfd;
> +
> +	abfd = bfd_openr(filename, NULL);
> +	if (!abfd)
> +		return -1;
> +
> +	if (!bfd_check_format(abfd, bfd_object)) {
> +		pr_debug2("%s: cannot read %s bfd file.\n", __func__, filename);
> +		goto out_close;
> +	}
> +
> +	section = bfd_get_section_by_name(abfd, ".gnu_debuglink");
> +	if (!section)
> +		goto out_close;
> +
> +	if (section->size > size)
> +		goto out_close;
> +
> +	if (!bfd_get_section_contents(abfd, section, debuglink, 0,
> +				      section->size))
> +		goto out_close;
> +
> +	err = 0;
> +
> +out_close:
> +	bfd_close(abfd);
> +	return err;
> +}
> +
> +#else
> +
>  int filename__read_debuglink(const char *filename, char *debuglink,
>  			     size_t size)
>  {
> @@ -660,6 +732,8 @@ int filename__read_debuglink(const char *filename, char *debuglink,
>  	return err;
>  }
>  
> +#endif
> +
>  static int dso__swap_init(struct dso *dso, unsigned char eidata)
>  {
>  	static unsigned int const endian = 1;
> -- 
> 2.28.0
>