perf tools: Fix copying of /proc/kcore]

Sorry, forgot the "vger.", but I guess it would be nice to have a forwarder from [email protected] to [email protected] :-)

- Arnaldo

----- Forwarded message from Arnaldo Carvalho de Melo <[email protected]> -----

Date: Fri, 25 Sep 2015 12:28:38 -0300
From: Arnaldo Carvalho de Melo <[email protected]>
Subject: [PATCH 3/3] perf tools: Fix copying of /proc/kcore
To: Ingo Molnar <[email protected]>
Cc: [email protected], Adrian Hunter <[email protected]>, Jiri Olsa <[email protected]>, [email protected], Arnaldo Carvalho de Melo
<[email protected]>

From: Adrian Hunter <[email protected]>

A copy of /proc/kcore containing the kernel text can be made to the buildid cache. e.g.

perf buildid-cache -v -k /proc/kcore

To workaround objdump limitations, a copy is also made when annotating against /proc/kcore.

The copying process stops working from libelf about v1.62 onwards (the problem was found with v1.63).

The cause is that a call to gelf_getphdr() in kcore__add_phdr() fails because additional validation has been added to gelf_getphdr().

The use of gelf_getphdr() is a misguided attempt to get default initialization of the Gelf_Phdr structure. That should not be necessary because every member of the Gelf_Phdr structure is subsequently assigned. So just remove the call to gelf_getphdr().

Similarly, a call to gelf_getehdr() in gelf_kcore__init() can be removed also.

Committer notes:

Note to [email protected], from Adrian in the cover letter for this patchkit:

The "Fix copying of /proc/kcore" problem goes back to v3.13 if you think it is important enough for stable.

---
 tools/perf/util/symbol-elf.c | 35 +++++++++++++----------------------
 1 file changed, 13 insertions(+), 22 deletions(-)

index f78ea3dc4c08..475d88d0a1c9 100644
@@ -1271,8 +1271,6 @@ out_close:
 static int kcore__init(struct kcore *kcore, char *filename, int elfclass,
 		       bool temp)
 {
-	GElf_Ehdr *ehdr;
-
 	kcore->elfclass = elfclass;
 
 	if (temp)

@@ -1289,9 +1287,7 @@ static int kcore__init(struct kcore *kcore, char *filename, int elfclass,
 	if (!gelf_newehdr(kcore->elf, elfclass))
 		goto out_end;
 
-	ehdr = gelf_getehdr(kcore->elf, &kcore->ehdr);
-	if (!ehdr)
-		goto out_end;
+	memset(&kcore->ehdr, 0, sizeof(GElf_Ehdr));
 
 	return 0;
 

@@ -1348,23 +1344,18 @@ static int kcore__copy_hdr(struct kcore *from, struct kcore *to, size_t count)
 static int kcore__add_phdr(struct kcore *kcore, int idx, off_t offset,
 			   u64 addr, u64 len)
 {
-	GElf_Phdr gphdr;
-	GElf_Phdr *phdr;
-
-	phdr = gelf_getphdr(kcore->elf, idx, &gphdr);
-	if (!phdr)
-		return -1;
-
-	phdr->p_type	= PT_LOAD;
-	phdr->p_flags	= PF_R | PF_W | PF_X;
-	phdr->p_offset	= offset;
-	phdr->p_vaddr	= addr;
-	phdr->p_paddr	= 0;
-	phdr->p_filesz	= len;
-	phdr->p_memsz	= len;
-	phdr->p_align	= page_size;
-
-	if (!gelf_update_phdr(kcore->elf, idx, phdr))
+	GElf_Phdr phdr = {
+		.p_type		= PT_LOAD,
+		.p_flags	= PF_R | PF_W | PF_X,
+		.p_offset	= offset,
+		.p_vaddr	= addr,
+		.p_paddr	= 0,
+		.p_filesz	= len,
+		.p_memsz	= len,
+		.p_align	= page_size,
+	};
+
+	if (!gelf_update_phdr(kcore->elf, idx, &phdr))
 		return -1;
 
 	return 0;

2.1.0

----- End forwarded message -----

My scripts know to pick up both of these, thanks, I got it now.

greg k-h

Em Tue, Oct 13, 2015 at 01:13:21PM -0700, Greg KH escreveu:

Great,

- Arnaldo