Re: libunwind-using-elfutils mail review

[Andrew Cagney <cagney at redhat dot com>]

Jan,

Looking at the changes:

@@ -348,7 +350,11 @@ extern int dwarf_init (void);
extern int dwarf_find_proc_info (unw_addr_space_t as, unw_word_t ip,
				 unw_proc_info_t *pi,
				 int need_unwind_info, void *arg);
+extern int dwarf_get_proc_name (unw_addr_space_t as, pid_t pid, unw_word_t ip,
+				char *buf, size_t buf_len, unw_word_t *offp,
+				void *arg);
extern int dwarf_search_unwind_table (unw_addr_space_t as,
+				      pid_t pid,
				      unw_word_t ip,
				      unw_dyn_info_t *di,
				      unw_proc_info_t *pi,

I'm guessing that the PID is added so that it can be passed through to 
elfutils and hence let elfutils access /proc/PID/maps and other local 
process information?  For libunwind, its the unw_accessor_t vector that 
should be used when accessing process information, and not access things 
directly.  This becomes important when, say,  "process" is a core-file, 
or when the "process" is on another system  - the unw_accessor_t methods 
provide the call-backs needed to extract the memory, and other 
information from the non-process.

Have you tried getting libunwind to use elfutils by overriding the 
unw_accessor_t methods:
 find_proc_info
 put_unwind_info
 get_proc_name
D-M-T's posts suggest is is, but looking at the changes you had to make 
to get libunwind working with elfutils then I'm wondering if there could 
be problems.  Perhaps you could provide a set of accessors, like the 
existing UPT accessors, for handling the local case using libunwind and 
elfutils.

The ability to override those methods with elf versions, is very 
important.  At present npremji is rewriting the libunwind bindings so 
that they can work properly remote - that is implementing a 
unw_accessors_t vector that obtains all information using frysk.proc 
and, hopefully, elfutils.  Once that is finished, the next step will be 
to re-iimplement the elfutils (libdwfl) bindings so that they too obtain 
their information from frysk.proc.

Andrew


For frysk, nurdin is currently preparing changes to

Jan Kratochvil wrote:
> Hi Andrew,
>
> please check the mail to <libunwind-devel@nongnu.org>.
>
> I would like to suggest some frysk's libunwind changes merge upstream...