linux-kernel - Re: [PATCH RFC RESEND] Perf: lookup dwarf unwind stack info in debug file pointed by .gnu

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Date:   Mon, 22 Aug 2016 17:19:19 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@...ia.com>
Cc:     acme@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC RESEND] Perf: lookup dwarf unwind stack info in debug
 file pointed by .gnu_debuglink

On Mon, Aug 22, 2016 at 02:32:04PM +0200, Matija Glavinic Pecotic wrote:

SNIP

> Signed-off-by: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@...ia.com>
> ---
>  tools/perf/util/unwind-libunwind-local.c | 36 ++++++++++++++++++++++++++++----
>  1 file changed, 32 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/unwind-libunwind-local.c b/tools/perf/util/unwind-libunwind-local.c
> index 97c0f8f..5d40acd 100644
> --- a/tools/perf/util/unwind-libunwind-local.c
> +++ b/tools/perf/util/unwind-libunwind-local.c
> @@ -35,6 +35,7 @@
>  #include "util.h"
>  #include "debug.h"
>  #include "asm/bug.h"
> +#include "dso.h"
>  
>  extern int
>  UNW_OBJ(dwarf_search_unwind_table) (unw_addr_space_t as,
> @@ -292,10 +293,13 @@ static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
>  
>  #ifndef NO_LIBUNWIND_DEBUG_FRAME
>  static int read_unwind_spec_debug_frame(struct dso *dso,
> -					struct machine *machine, u64 *offset)
> +					struct machine *machine, u64 *offset,
> +					char **symfile)
>  {
>  	int fd;
>  	u64 ofs = dso->data.debug_frame_offset;
> +	char *debuglink = malloc(PATH_MAX);
> +	int ret = 0;
>  
>  	if (ofs == 0) {
>  		fd = dso__data_get_fd(dso, machine);
> @@ -312,6 +316,26 @@ static int read_unwind_spec_debug_frame(struct dso *dso,
>  	if (*offset)
>  		return 0;
>  
> +	/* If not found, try to lookup in debuglink */
> +	ret = dso__read_binary_type_filename(
> +			dso, DSO_BINARY_TYPE__DEBUGLINK,
> +			machine->root_dir, debuglink, PATH_MAX);
> +	if (!ret) {
> +		pr_debug("%s: dso: %s, ret: %d, debuglink: <%s>\n",
> +			__func__, dso->short_name, ret, debuglink);
> +
> +		fd = open(debuglink, O_RDONLY);
> +		if (fd >= 0) {
> +			ofs = elf_section_offset(fd, ".debug_frame");
> +			close(fd);

should you also set following?

	*offset = ofs
	dso->debug_frame_offset = ofs;

I guess if we found the debuglink section with file having .debug_frame
section, we want to use it for this dso from now on..

I'd think let's have read_unwind_spec_debug_frame to find .debug_frame
and provide that info under dso object for subsequent reads

> +
> +			if (ofs) {
> +				*symfile = debuglink;
> +				return 0;
> +			}
> +		}
> +	}
> +
>  	return -EINVAL;
>  }
>  #endif
> @@ -343,6 +367,7 @@ find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
>  	unw_dyn_info_t di;
>  	u64 table_data, segbase, fde_count;
>  	int ret = -EINVAL;
> +	char *symfile = NULL;
>  
>  	map = find_map(ip, ui);
>  	if (!map || !map->dso)
> @@ -368,16 +393,19 @@ find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
>  #ifndef NO_LIBUNWIND_DEBUG_FRAME
>  	/* Check the .debug_frame section for unwinding info */
>  	if (ret < 0 &&
> -	    !read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
> +	    !read_unwind_spec_debug_frame(
> +		    map->dso, ui->machine, &segbase, &symfile)) {
>  		int fd = dso__data_get_fd(map->dso, ui->machine);
>  		int is_exec = elf_is_exec(fd, map->dso->name);
>  		unw_word_t base = is_exec ? 0 : map->start;
> -		const char *symfile;
>  
>  		if (fd >= 0)
>  			dso__data_put_fd(map->dso);
>  
> -		symfile = map->dso->symsrc_filename ?: map->dso->name;
> +		if (!symfile)
> +			symfile = map->dso->symsrc_filename ?: map->dso->name;

so in case we find debuglink-ed file, it has precedence over the file
we found symtab in? assuming thats what dso->symsrc_filename is..

thanks,
jirka