Yet another pahole crash

Yet another pahole crash

[Diego E. “Flameeyes” Pettenò]

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Trying to debug some problems I found a fun crash in pahole. The file
producing the error is available at
http://www.flameeyes.eu/tmp/feng.pahole.crasher.20090508.bz2

Have fun!

-- 
Diego Elio Pettenò — “Flameeyes”
http://blog.flameeyes.eu/

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Re: Yet another pahole crash

[Arnaldo Carvalho de Melo]

Em Fri, May 08, 2009 at 01:29:34AM +0200, Diego E. “Flameeyes” Pettenò escreveu:
> Trying to debug some problems I found a fun crash in pahole. The file
> producing the error is available at
> http://www.flameeyes.eu/tmp/feng.pahole.crasher.20090508.bz2

You forgot to mention that this is only when you ask for the anonymous structs:

[acme@doppio object_samples]$ pahole --anon_include feng.pahole.crasher.20090508
<BIG SNIP>
typedef struct {
	sock_type                  socktype;        /*     0     4 */
	int                        fd;              /*     4     4 */
	struct sockaddr_storage    local_stg;       /*     8   128 */
	/* --- cacheline 2 boundary (128 bytes) was 8 bytes ago --- */
	struct sockaddr_storage    remote_stg;      /*   136   128 */
	/* --- cacheline 4 boundary (256 bytes) was 8 bytes ago --- */
	struct sockaddr_storage    multicast_stg;   /*   264   128 */
	/* --- cacheline 6 boundary (384 bytes) was 8 bytes ago --- */
	sock_flags                 flags;           /*   392     4 */

	/* XXX 4 bytes hole, try to pack */

	char *                     remote_host;     /*   400     8 */
	char *                     local_host;      /*   408     8 */
	in_port_t                  remote_port;     /*   416     2 */
	in_port_t                  local_port;      /*   418     2 */

	/* XXX 4 bytes hole, try to pack */

	void *                     ssl;             /*   424     8 */
	void *                     data;            /*   432     8 */

	/* size: 440, cachelines: 7, members: 12 */
	/* sum members: 432, holes: 2, sum holes: 8 */
	/* last cacheline: 56 bytes */
} Sock;
Segmentation fault
[acme@doppio object_samples]$ pahole -Aa feng.pahole.crasher.20090508

Must be some bug I introduced in the last month or so, investigating.
 
> Have fun!

Having.

- Arnaldo
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Re: Yet another pahole crash

[Arnaldo Carvalho de Melo]

Em Fri, May 08, 2009 at 12:54:08AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Fri, May 08, 2009 at 01:29:34AM +0200, Diego E. “Flameeyes” Pettenò escreveu:
> > Trying to debug some problems I found a fun crash in pahole. The file
> > producing the error is available at
> > http://www.flameeyes.eu/tmp/feng.pahole.crasher.20090508.bz2
> 
> You forgot to mention that this is only when you ask for the anonymous structs:
> 
> [acme@doppio object_samples]$ pahole --anon_include feng.pahole.crasher.20090508
> <BIG SNIP>
> typedef struct {
> 	sock_type                  socktype;        /*     0     4 */
> 	int                        fd;              /*     4     4 */
> 	struct sockaddr_storage    local_stg;       /*     8   128 */
> 	/* --- cacheline 2 boundary (128 bytes) was 8 bytes ago --- */
> 	struct sockaddr_storage    remote_stg;      /*   136   128 */
> 	/* --- cacheline 4 boundary (256 bytes) was 8 bytes ago --- */
> 	struct sockaddr_storage    multicast_stg;   /*   264   128 */
> 	/* --- cacheline 6 boundary (384 bytes) was 8 bytes ago --- */
> 	sock_flags                 flags;           /*   392     4 */
> 
> 	/* XXX 4 bytes hole, try to pack */
> 
> 	char *                     remote_host;     /*   400     8 */
> 	char *                     local_host;      /*   408     8 */
> 	in_port_t                  remote_port;     /*   416     2 */
> 	in_port_t                  local_port;      /*   418     2 */
> 
> 	/* XXX 4 bytes hole, try to pack */
> 
> 	void *                     ssl;             /*   424     8 */
> 	void *                     data;            /*   432     8 */
> 
> 	/* size: 440, cachelines: 7, members: 12 */
> 	/* sum members: 432, holes: 2, sum holes: 8 */
> 	/* last cacheline: 56 bytes */
> } Sock;
> Segmentation fault
> [acme@doppio object_samples]$ pahole -Aa feng.pahole.crasher.20090508
> 
> Must be some bug I introduced in the last month or so, investigating.
>  
> > Have fun!
> 
> Having.

Put a bandaid for now, only side effect, obvious for a multi-object file like this:

$ readelf -wi feng.pahole.crasher.20090508 | grep DW_TAG_compile_unit | wc -l
56

Is that anonymous structs will be printed for every CU where they are defined:

$ pahole --anon_include feng.pahole.crasher.20090508  | grep '} server_config' | wc -l
18

Yes, avoiding duplicates by looking for the same name always was, hum, lame and
could avoid printing a different struct that has the same name (as
unlikely/stupid as this may be, its possible), I'll get that properly fixed
soon.

And here is the bandaid, for reference, already commited and pushed, thanks one
more time for reporting Diego!

- Arnaldo

[acme@doppio pahole]$ git-diff
diff --git a/pahole.c b/pahole.c
index 0ba7dde..1c0eef8 100644
--- a/pahole.c
+++ b/pahole.c
@@ -295,6 +295,16 @@ static void print_classes(struct cu *cu)
                        print_packable_info(pos, cu, id);
                else if (formatter != NULL)
                        formatter(pos, cu, id);
+               /*
+                * FIXME: No sense in adding an anonymous struct to the list of
+                * structs already printed, as we look for the name... The
+                * right fix probably will be to call class__fprintf on a
+                * in-memory FILE, do a hash, and look it by full contents, not
+                * by name. And this is needed for CTF as well, but its late now
+                * and I'm sleepy, will leave for later...
+                */
+               if (pos->type.namespace.name == 0)
+                       continue;
 
                if (structures__add(pos, cu) == NULL) {
                        fprintf(stderr, "pahole: insufficient memory for "

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