[PATCH 2/2] perf tools: Fix copying of /proc/kcore

From: Adrian Hunter
Date: Thu Sep 24 2015 - 06:08:49 EST


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.

Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
---
tools/perf/util/symbol-elf.c | 35 +++++++++++++----------------------
1 file changed, 13 insertions(+), 22 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index f78ea3dc4c08..475d88d0a1c9 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -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;
--
1.9.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/