[PATCH v2 00/12] Add build ID to stacktraces

[PATCH v2 00/12] Add build ID to stacktraces

[Stephen Boyd]

This series adds the kernel's build ID[1] to the stacktrace header printed
in oops messages, warnings, etc. and the build ID for any module that
appears in the stacktrace after the module name. The goal is to make the
stacktrace more self-contained and descriptive by including the relevant
build IDs in the kernel logs when something goes wrong. This can be used
by post processing tools like script/decode_stacktrace.sh and kernel
developers to easily locate the debug info associated with a kernel
crash and line up what line and file things started falling apart at.

To show how this can be used I've included a patch to
decode_stacktrace.sh that downloads the debuginfo from a debuginfod
server.

This also includes some patches to make the buildid.c file use more
const arguments and consolidate logic into buildid.c from kdump. These
are left to the end as they were mostly cleanup patches. I don't know
who exactly maintains this so I guess Andrew is the best option to merge
all this code.

Here's an example lkdtm stacktrace on arm64.

 WARNING: CPU: 4 PID: 3255 at drivers/misc/lkdtm/bugs.c:83 lkdtm_WARNING+0x28/0x30 [lkdtm]
 Modules linked in: lkdtm rfcomm algif_hash algif_skcipher af_alg xt_cgroup uinput xt_MASQUERADE
 CPU: 4 PID: 3255 Comm: bash Not tainted 5.11 #3 aa23f7a1231c229de205662d5a9e0d4c580f19a1
 Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
 pstate: 00400009 (nzcv daif +PAN -UAO -TCO BTYPE=--)
 pc : lkdtm_WARNING+0x28/0x30 [lkdtm]
 lr : lkdtm_do_action+0x24/0x40 [lkdtm]
 sp : ffffffc0134fbca0
 x29: ffffffc0134fbca0 x28: ffffff92d53ba240
 x27: 0000000000000000 x26: 0000000000000000
 x25: 0000000000000000 x24: ffffffe3622352c0
 x23: 0000000000000020 x22: ffffffe362233366
 x21: ffffffe3622352e0 x20: ffffffc0134fbde0
 x19: 0000000000000008 x18: 0000000000000000
 x17: ffffff929b6536fc x16: 0000000000000000
 x15: 0000000000000000 x14: 0000000000000012
 x13: ffffffe380ed892c x12: ffffffe381d05068
 x11: 0000000000000000 x10: 0000000000000000
 x9 : 0000000000000001 x8 : ffffffe362237000
 x7 : aaaaaaaaaaaaaaaa x6 : 0000000000000000
 x5 : 0000000000000000 x4 : 0000000000000001
 x3 : 0000000000000008 x2 : ffffff93fef25a70
 x1 : ffffff93fef15788 x0 : ffffffe3622352e0
 Call trace:
  lkdtm_WARNING+0x28/0x30 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]
  direct_entry+0x16c/0x1b4 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]
  full_proxy_write+0x74/0xa4
  vfs_write+0xec/0x2e8
  ksys_write+0x84/0xf0
  __arm64_sys_write+0x24/0x30
  el0_svc_common+0xf4/0x1c0
  do_el0_svc_compat+0x28/0x3c
  el0_svc_compat+0x10/0x1c
  el0_sync_compat_handler+0xa8/0xcc
  el0_sync_compat+0x178/0x180
 ---[ end trace 3d95032303e59e68 ]---

Changes from v1 (https://lore.kernel.org/r/20210301174749.1269154-1-swboyd@chromium.org):
 * New printk format %pSb and %pSr
 * Return binary format instead of hex format string from build ID APIs
 * Some new patches to cleanup buildid/decode_stacktrace.sh
 * A new patch to decode_stacktrace.sh to parse output

[1] https://fedoraproject.org/wiki/Releases/FeatureBuildId

Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Evan Green <evgreen@chromium.org>
Cc: Hsin-Yi Wang <hsinyi@chromium.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: <kexec@lists.infradead.org>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: <linux-arm-kernel@lists.infradead.org>
Cc: <linux-doc@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: <x86@kernel.org>

Stephen Boyd (12):
  buildid: Add API to parse build ID out of buffer
  buildid: Add method to get running kernel's build ID
  dump_stack: Add vmlinux build ID to stack traces
  module: Add printk format to add module build ID to stacktraces
  arm64: stacktrace: Use %pSb for backtrace printing
  x86/dumpstack: Use %pSb for backtrace printing
  scripts/decode_stacktrace.sh: Support debuginfod
  scripts/decode_stacktrace.sh: Silence stderr messages from
    addr2line/nm
  scripts/decode_stacktrace.sh: Indicate 'auto' can be used for base
    path
  buildid: Mark some arguments const
  buildid: Fix kernel-doc notation
  kdump: Use vmlinux_build_id() to simplify

 Documentation/core-api/printk-formats.rst |  9 +++
 arch/arm64/kernel/stacktrace.c            |  2 +-
 arch/x86/kernel/dumpstack.c               |  4 +-
 include/linux/buildid.h                   |  3 +
 include/linux/crash_core.h                |  6 +-
 include/linux/kallsyms.h                  | 13 +++-
 include/linux/module.h                    |  6 +-
 kernel/crash_core.c                       | 41 +----------
 kernel/kallsyms.c                         | 73 ++++++++++++++-----
 kernel/module.c                           | 24 +++++-
 lib/buildid.c                             | 75 +++++++++++++++----
 lib/dump_stack.c                          |  5 +-
 lib/vsprintf.c                            |  6 +-
 scripts/decode_stacktrace.sh              | 89 +++++++++++++++++++----
 14 files changed, 251 insertions(+), 105 deletions(-)


base-commit: a38fd8748464831584a19438cbb3082b5a2dab15
-- 
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[PATCH v2 02/12] buildid: Add method to get running kernel's build ID

[Stephen Boyd]

Add vmlinux_build_id() so that callers can print a hex format string
representation of the running kernel's build ID. This will be used in
the kdump and dump_stack code so that developers can easily locate the
vmlinux debug symbols for a crash/stacktrace.

Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Evan Green <evgreen@chromium.org>
Cc: Hsin-Yi Wang <hsinyi@chromium.org>
Cc: Dave Young <dyoung@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: <kexec@lists.infradead.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
---
 include/linux/buildid.h |  2 ++
 lib/buildid.c           | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/linux/buildid.h b/include/linux/buildid.h
index ebce93f26d06..2ff6b1b7cc9b 100644
--- a/include/linux/buildid.h
+++ b/include/linux/buildid.h
@@ -10,4 +10,6 @@ int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
 		   __u32 *size);
 int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size);
 
+const unsigned char *vmlinux_build_id(void);
+
 #endif
diff --git a/lib/buildid.c b/lib/buildid.c
index 010ab0674cb9..fa1b6466b4b8 100644
--- a/lib/buildid.c
+++ b/lib/buildid.c
@@ -4,6 +4,7 @@
 #include <linux/elf.h>
 #include <linux/kernel.h>
 #include <linux/pagemap.h>
+#include <linux/string.h>
 
 #define BUILD_ID 3
 
@@ -171,3 +172,21 @@ int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size)
 {
 	return parse_build_id_buf(build_id, NULL, buf, buf_size);
 }
+
+/**
+ * vmlinux_build_id - Get the running kernel's build ID
+ *
+ * Return: Running kernel's build ID
+ */
+const unsigned char *vmlinux_build_id(void)
+{
+	extern const void __start_notes __weak;
+	extern const void __stop_notes __weak;
+	unsigned int size = &__stop_notes - &__start_notes;
+	static unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX];
+
+	if (!memchr_inv(vmlinux_build_id, 0, BUILD_ID_SIZE_MAX))
+		build_id_parse_buf(&__start_notes, vmlinux_build_id, size);
+
+	return vmlinux_build_id;
+}
-- 
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Re: [PATCH v2 02/12] buildid: Add method to get running kernel's build ID

[Rasmus Villemoes]

On 24/03/2021 03.04, Stephen Boyd wrote:
> Add vmlinux_build_id() so that callers can print a hex format string
> representation of the running kernel's build ID. This will be used in
> the kdump and dump_stack code so that developers can easily locate the
> vmlinux debug symbols for a crash/stacktrace.
> 
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Jessica Yu <jeyu@kernel.org>
> Cc: Evan Green <evgreen@chromium.org>
> Cc: Hsin-Yi Wang <hsinyi@chromium.org>
> Cc: Dave Young <dyoung@redhat.com>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: <kexec@lists.infradead.org>
> Signed-off-by: Stephen Boyd <swboyd@chromium.org>
> ---
>  include/linux/buildid.h |  2 ++
>  lib/buildid.c           | 19 +++++++++++++++++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/include/linux/buildid.h b/include/linux/buildid.h
> index ebce93f26d06..2ff6b1b7cc9b 100644
> --- a/include/linux/buildid.h
> +++ b/include/linux/buildid.h
> @@ -10,4 +10,6 @@ int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
>  		   __u32 *size);
>  int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size);
>  
> +const unsigned char *vmlinux_build_id(void);
> +
>  #endif
> diff --git a/lib/buildid.c b/lib/buildid.c
> index 010ab0674cb9..fa1b6466b4b8 100644
> --- a/lib/buildid.c
> +++ b/lib/buildid.c
> @@ -4,6 +4,7 @@
>  #include <linux/elf.h>
>  #include <linux/kernel.h>
>  #include <linux/pagemap.h>
> +#include <linux/string.h>
>  
>  #define BUILD_ID 3
>  
> @@ -171,3 +172,21 @@ int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size)
>  {
>  	return parse_build_id_buf(build_id, NULL, buf, buf_size);
>  }
> +
> +/**
> + * vmlinux_build_id - Get the running kernel's build ID
> + *
> + * Return: Running kernel's build ID
> + */
> +const unsigned char *vmlinux_build_id(void)
> +{
> +	extern const void __start_notes __weak;
> +	extern const void __stop_notes __weak;
> +	unsigned int size = &__stop_notes - &__start_notes;
> +	static unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX];
> +
> +	if (!memchr_inv(vmlinux_build_id, 0, BUILD_ID_SIZE_MAX))
> +		build_id_parse_buf(&__start_notes, vmlinux_build_id, size);
> +
> +	return vmlinux_build_id;
> +}
> 

Hm, is there any reason to do that initialization lazily and thus need
an accessor? If the system is coming down hard, there's a (very very
small) risk that one thread starts finding the build id, is in the
middle of the memcpy, another thread also ends up wanting the vmlinux
build id, sees some non-nul byte, and proceeds to using the partially
written vmlinux_build_id.

Perhaps consider just exposing the vmlinux_build_id[] array itself,
adding a init_vmlinux_build_id() call somewhere early in start_kernel().

It could then also be made __ro_after_init.

In any case, if you decide to keep the current way, please rename the
local variable (just "build_id" is fine) so that it doesn't shadow the
very function it resides in, that's very confusing.

Rasmus

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Re: [PATCH v2 02/12] buildid: Add method to get running kernel's build ID

[Stephen Boyd]

Quoting Rasmus Villemoes (2021-03-24 02:24:27)
> On 24/03/2021 03.04, Stephen Boyd wrote:
> > Add vmlinux_build_id() so that callers can print a hex format string
> > representation of the running kernel's build ID. This will be used in
> > the kdump and dump_stack code so that developers can easily locate the
> > vmlinux debug symbols for a crash/stacktrace.
> > 
> > Cc: Jiri Olsa <jolsa@kernel.org>
> > Cc: Alexei Starovoitov <ast@kernel.org>
> > Cc: Jessica Yu <jeyu@kernel.org>
> > Cc: Evan Green <evgreen@chromium.org>
> > Cc: Hsin-Yi Wang <hsinyi@chromium.org>
> > Cc: Dave Young <dyoung@redhat.com>
> > Cc: Baoquan He <bhe@redhat.com>
> > Cc: Vivek Goyal <vgoyal@redhat.com>
> > Cc: <kexec@lists.infradead.org>
> > Signed-off-by: Stephen Boyd <swboyd@chromium.org>
> > ---
> >  include/linux/buildid.h |  2 ++
> >  lib/buildid.c           | 19 +++++++++++++++++++
> >  2 files changed, 21 insertions(+)
> > 
> > diff --git a/include/linux/buildid.h b/include/linux/buildid.h
> > index ebce93f26d06..2ff6b1b7cc9b 100644
> > --- a/include/linux/buildid.h
> > +++ b/include/linux/buildid.h
> > @@ -10,4 +10,6 @@ int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
> >                  __u32 *size);
> >  int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size);
> >  
> > +const unsigned char *vmlinux_build_id(void);
> > +
> >  #endif
> > diff --git a/lib/buildid.c b/lib/buildid.c
> > index 010ab0674cb9..fa1b6466b4b8 100644
> > --- a/lib/buildid.c
> > +++ b/lib/buildid.c
> > @@ -4,6 +4,7 @@
> >  #include <linux/elf.h>
> >  #include <linux/kernel.h>
> >  #include <linux/pagemap.h>
> > +#include <linux/string.h>
> >  
> >  #define BUILD_ID 3
> >  
> > @@ -171,3 +172,21 @@ int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size)
> >  {
> >       return parse_build_id_buf(build_id, NULL, buf, buf_size);
> >  }
> > +
> > +/**
> > + * vmlinux_build_id - Get the running kernel's build ID
> > + *
> > + * Return: Running kernel's build ID
> > + */
> > +const unsigned char *vmlinux_build_id(void)
> > +{
> > +     extern const void __start_notes __weak;
> > +     extern const void __stop_notes __weak;
> > +     unsigned int size = &__stop_notes - &__start_notes;
> > +     static unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX];
> > +
> > +     if (!memchr_inv(vmlinux_build_id, 0, BUILD_ID_SIZE_MAX))
> > +             build_id_parse_buf(&__start_notes, vmlinux_build_id, size);
> > +
> > +     return vmlinux_build_id;
> > +}
> > 
> 
> Hm, is there any reason to do that initialization lazily and thus need
> an accessor? If the system is coming down hard, there's a (very very
> small) risk that one thread starts finding the build id, is in the
> middle of the memcpy, another thread also ends up wanting the vmlinux
> build id, sees some non-nul byte, and proceeds to using the partially
> written vmlinux_build_id.
> 
> Perhaps consider just exposing the vmlinux_build_id[] array itself,
> adding a init_vmlinux_build_id() call somewhere early in start_kernel().
> 
> It could then also be made __ro_after_init.
> 
> In any case, if you decide to keep the current way, please rename the
> local variable (just "build_id" is fine) so that it doesn't shadow the
> very function it resides in, that's very confusing.
> 

No particular reason to do it this way. I'll take that approach to
initialize it early in start_kernel() and then expose the array instead.
Thanks!

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[PATCH v2 12/12] kdump: Use vmlinux_build_id() to simplify

[Stephen Boyd]

We can use the vmlinux_build_id() helper here now instead of open coding
it. This consolidates code and possibly avoids calculating the build ID
twice in the case of a crash with a stacktrace.

Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Evan Green <evgreen@chromium.org>
Cc: Hsin-Yi Wang <hsinyi@chromium.org>
Cc: Dave Young <dyoung@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: <kexec@lists.infradead.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
---
 include/linux/crash_core.h |  6 +-----
 kernel/crash_core.c        | 41 ++------------------------------------
 2 files changed, 3 insertions(+), 44 deletions(-)

diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index 206bde8308b2..fb8ab99bb2ee 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -39,7 +39,7 @@ phys_addr_t paddr_vmcoreinfo_note(void);
 #define VMCOREINFO_OSRELEASE(value) \
 	vmcoreinfo_append_str("OSRELEASE=%s\n", value)
 #define VMCOREINFO_BUILD_ID(value) \
-	vmcoreinfo_append_str("BUILD-ID=%s\n", value)
+	vmcoreinfo_append_str("BUILD-ID=%20phN\n", value)
 #define VMCOREINFO_PAGESIZE(value) \
 	vmcoreinfo_append_str("PAGESIZE=%ld\n", value)
 #define VMCOREINFO_SYMBOL(name) \
@@ -69,10 +69,6 @@ extern unsigned char *vmcoreinfo_data;
 extern size_t vmcoreinfo_size;
 extern u32 *vmcoreinfo_note;
 
-/* raw contents of kernel .notes section */
-extern const void __start_notes __weak;
-extern const void __stop_notes __weak;
-
 Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
 			  void *data, size_t data_len);
 void final_note(Elf_Word *buf);
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 825284baaf46..0b0e24668697 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -4,6 +4,7 @@
  * Copyright (C) 2002-2004 Eric Biederman  <ebiederm@xmission.com>
  */
 
+#include <linux/buildid.h>
 #include <linux/crash_core.h>
 #include <linux/utsname.h>
 #include <linux/vmalloc.h>
@@ -378,51 +379,13 @@ phys_addr_t __weak paddr_vmcoreinfo_note(void)
 }
 EXPORT_SYMBOL(paddr_vmcoreinfo_note);
 
-#define NOTES_SIZE (&__stop_notes - &__start_notes)
-#define BUILD_ID_MAX SHA1_DIGEST_SIZE
-#define NT_GNU_BUILD_ID 3
-
-struct elf_note_section {
-	struct elf_note	n_hdr;
-	u8 n_data[];
-};
-
 /*
  * Add build ID from .notes section as generated by the GNU ld(1)
  * or LLVM lld(1) --build-id option.
  */
 static void add_build_id_vmcoreinfo(void)
 {
-	char build_id[BUILD_ID_MAX * 2 + 1];
-	int n_remain = NOTES_SIZE;
-
-	while (n_remain >= sizeof(struct elf_note)) {
-		const struct elf_note_section *note_sec =
-			&__start_notes + NOTES_SIZE - n_remain;
-		const u32 n_namesz = note_sec->n_hdr.n_namesz;
-
-		if (note_sec->n_hdr.n_type == NT_GNU_BUILD_ID &&
-		    n_namesz != 0 &&
-		    !strcmp((char *)&note_sec->n_data[0], "GNU")) {
-			if (note_sec->n_hdr.n_descsz <= BUILD_ID_MAX) {
-				const u32 n_descsz = note_sec->n_hdr.n_descsz;
-				const u8 *s = &note_sec->n_data[n_namesz];
-
-				s = PTR_ALIGN(s, 4);
-				bin2hex(build_id, s, n_descsz);
-				build_id[2 * n_descsz] = '\0';
-				VMCOREINFO_BUILD_ID(build_id);
-				return;
-			}
-			pr_warn("Build ID is too large to include in vmcoreinfo: %u > %u\n",
-				note_sec->n_hdr.n_descsz,
-				BUILD_ID_MAX);
-			return;
-		}
-		n_remain -= sizeof(struct elf_note) +
-			ALIGN(note_sec->n_hdr.n_namesz, 4) +
-			ALIGN(note_sec->n_hdr.n_descsz, 4);
-	}
+	VMCOREINFO_BUILD_ID(vmlinux_build_id());
 }
 
 static int __init crash_save_vmcoreinfo_init(void)
-- 
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Re: [PATCH v2 00/12] Add build ID to stacktraces

[Christoph Hellwig]

On Tue, Mar 23, 2021 at 07:04:31PM -0700, Stephen Boyd wrote:
>  x5 : 0000000000000000 x4 : 0000000000000001
>  x3 : 0000000000000008 x2 : ffffff93fef25a70
>  x1 : ffffff93fef15788 x0 : ffffffe3622352e0
>  Call trace:
>   lkdtm_WARNING+0x28/0x30 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]
>   direct_entry+0x16c/0x1b4 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]

Yikes.  No, please do not make the backtraces a complete mess for
something that serves absolutely no need.

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Re: [PATCH v2 00/12] Add build ID to stacktraces

[peter enderborg]

On 3/24/21 9:55 AM, Christoph Hellwig wrote:
> On Tue, Mar 23, 2021 at 07:04:31PM -0700, Stephen Boyd wrote:
>>  x5 : 0000000000000000 x4 : 0000000000000001
>>  x3 : 0000000000000008 x2 : ffffff93fef25a70
>>  x1 : ffffff93fef15788 x0 : ffffffe3622352e0
>>  Call trace:
>>   lkdtm_WARNING+0x28/0x30 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]
>>   direct_entry+0x16c/0x1b4 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]
> Yikes.  No, please do not make the backtraces a complete mess for
> something that serves absolutely no need.

Would a "verbose" flag be acceptable solution?    Something like write 1 to /sys/kernel/debug/verbose_stack to get the extra info.

I think I see a need for it.


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Re: [PATCH v2 00/12] Add build ID to stacktraces

[Stephen Boyd]

Quoting peter enderborg (2021-03-25 04:06:17)
> On 3/24/21 9:55 AM, Christoph Hellwig wrote:
> > On Tue, Mar 23, 2021 at 07:04:31PM -0700, Stephen Boyd wrote:
> >>  x5 : 0000000000000000 x4 : 0000000000000001
> >>  x3 : 0000000000000008 x2 : ffffff93fef25a70
> >>  x1 : ffffff93fef15788 x0 : ffffffe3622352e0
> >>  Call trace:
> >>   lkdtm_WARNING+0x28/0x30 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]
> >>   direct_entry+0x16c/0x1b4 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]
> > Yikes.  No, please do not make the backtraces a complete mess for
> > something that serves absolutely no need.

It serves a need. Please look at the patches to understand that I'm
adding the buildid to automatically find the associated debug
information on distros.

> 
> Would a "verbose" flag be acceptable solution?    Something like write 1 to /sys/kernel/debug/verbose_stack to get the extra info.
> 
> I think I see a need for it.
> 

Or a kernel config option and a commandline parameter? That would be OK
for me as I said on v1 of this series. I'll add that in for the next
patch series given all the distaste for some more hex characters next to
the module name.

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Re: [PATCH v2 00/12] Add build ID to stacktraces

[Petr Mladek]

On Thu 2021-03-25 16:21:46, Stephen Boyd wrote:
> Quoting peter enderborg (2021-03-25 04:06:17)
> > On 3/24/21 9:55 AM, Christoph Hellwig wrote:
> > > On Tue, Mar 23, 2021 at 07:04:31PM -0700, Stephen Boyd wrote:
> > >>  x5 : 0000000000000000 x4 : 0000000000000001
> > >>  x3 : 0000000000000008 x2 : ffffff93fef25a70
> > >>  x1 : ffffff93fef15788 x0 : ffffffe3622352e0
> > >>  Call trace:
> > >>   lkdtm_WARNING+0x28/0x30 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]
> > >>   direct_entry+0x16c/0x1b4 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]
> > > Yikes.  No, please do not make the backtraces a complete mess for
> > > something that serves absolutely no need.
> 
> It serves a need. Please look at the patches to understand that I'm
> adding the buildid to automatically find the associated debug
> information on distros.
> 
> > 
> > Would a "verbose" flag be acceptable solution?    Something like write 1 to /sys/kernel/debug/verbose_stack to get the extra info.
> > 
> > I think I see a need for it.
> > 
> 
> Or a kernel config option and a commandline parameter? That would be OK
> for me as I said on v1 of this series. I'll add that in for the next
> patch series given all the distaste for some more hex characters next to
> the module name.

IMHO, a build configure option would fit the best here.

It does not make sense to show the ID when the kernel vendor does
not have a service to download the related binaries. But it makes
sense to show the buildid by default when the provider/distro has
the service and want to use the ID when handling bug reports.

We could always add boot/run time options when people really need it.

Best Regards,
Petr

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Re: [PATCH v2 00/12] Add build ID to stacktraces

[Stephen Boyd]

HTML mail?

Quoting Konstantin Khlebnikov (2021-03-24 01:23:55)
> 24.03.2021, 05:04, "Stephen Boyd" <swboyd@chromium.org>:
>  
> Looks too noisy for me. Maybe print id in the line "Modules linked in:"?
> I suppose only out-of-tree modules need this?
>  

Please see this note in patch 4:

Originally, I put this on the %pS format, but that was quickly rejected
given that %pS is used in other places such as ftrace where build IDs
aren't meaningful. There was some discussions on the list to put every
module build ID into the "Modules linked in:" section of the stacktrace
message but that quickly becomes very hard to read once you have more
than three or four modules linked in. It also provides too much
information when we don't expect each module to be traversed in a
stacktrace. Having the build ID for modules that aren't important just
makes things messy. Splitting it to multiple lines for each module
quickly explodes the number of lines printed in an oops too, possibly
wrapping the warning off the console. And finally, trying to stash away
each module used in a callstack to provide the ID of each symbol printed
is cumbersome and would require changes to each architecture to stash
away modules and return their build IDs once unwinding has completed.

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Re: [PATCH v2 00/12] Add build ID to stacktraces

[peter enderborg]

On 3/24/21 3:04 AM, Stephen Boyd wrote:
> This series adds the kernel's build ID[1] to the stacktrace header printed
> in oops messages, warnings, etc. and the build ID for any module that
> appears in the stacktrace after the module name. The goal is to make the
> stacktrace more self-contained and descriptive by including the relevant
> build IDs in the kernel logs when something goes wrong. This can be used
> by post processing tools like script/decode_stacktrace.sh and kernel
> developers to easily locate the debug info associated with a kernel
> crash and line up what line and file things started falling apart at.
>
> To show how this can be used I've included a patch to
> decode_stacktrace.sh that downloads the debuginfo from a debuginfod
> server.
>
> This also includes some patches to make the buildid.c file use more
> const arguments and consolidate logic into buildid.c from kdump. These
> are left to the end as they were mostly cleanup patches. I don't know
> who exactly maintains this so I guess Andrew is the best option to merge
> all this code.
>
> Here's an example lkdtm stacktrace on arm64.
>
>  WARNING: CPU: 4 PID: 3255 at drivers/misc/lkdtm/bugs.c:83 lkdtm_WARNING+0x28/0x30 [lkdtm]
>  Modules linked in: lkdtm rfcomm algif_hash algif_skcipher af_alg xt_cgroup uinput xt_MASQUERADE
>  CPU: 4 PID: 3255 Comm: bash Not tainted 5.11 #3 aa23f7a1231c229de205662d5a9e0d4c580f19a1
>  Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
>  pstate: 00400009 (nzcv daif +PAN -UAO -TCO BTYPE=--)
>  pc : lkdtm_WARNING+0x28/0x30 [lkdtm]
>  lr : lkdtm_do_action+0x24/0x40 [lkdtm]
>  sp : ffffffc0134fbca0
>  x29: ffffffc0134fbca0 x28: ffffff92d53ba240
>  x27: 0000000000000000 x26: 0000000000000000
>  x25: 0000000000000000 x24: ffffffe3622352c0
>  x23: 0000000000000020 x22: ffffffe362233366
>  x21: ffffffe3622352e0 x20: ffffffc0134fbde0
>  x19: 0000000000000008 x18: 0000000000000000
>  x17: ffffff929b6536fc x16: 0000000000000000
>  x15: 0000000000000000 x14: 0000000000000012
>  x13: ffffffe380ed892c x12: ffffffe381d05068
>  x11: 0000000000000000 x10: 0000000000000000
>  x9 : 0000000000000001 x8 : ffffffe362237000
>  x7 : aaaaaaaaaaaaaaaa x6 : 0000000000000000
>  x5 : 0000000000000000 x4 : 0000000000000001
>  x3 : 0000000000000008 x2 : ffffff93fef25a70
>  x1 : ffffff93fef15788 x0 : ffffffe3622352e0
>  Call trace:
>   lkdtm_WARNING+0x28/0x30 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]
>   direct_entry+0x16c/0x1b4 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]
>   full_proxy_write+0x74/0xa4
>   vfs_write+0xec/0x2e8
>   ksys_write+0x84/0xf0
>   __arm64_sys_write+0x24/0x30
>   el0_svc_common+0xf4/0x1c0
>   do_el0_svc_compat+0x28/0x3c
>   el0_svc_compat+0x10/0x1c
>   el0_sync_compat_handler+0xa8/0xcc
>   el0_sync_compat+0x178/0x180
>  ---[ end trace 3d95032303e59e68 ]---

How will this work with the ftrace?


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Re: [PATCH v2 00/12] Add build ID to stacktraces

[Stephen Boyd]

Quoting peter enderborg (2021-03-25 04:14:31)
> >   el0_sync_compat_handler+0xa8/0xcc
> >   el0_sync_compat+0x178/0x180
> >  ---[ end trace 3d95032303e59e68 ]---
> 
> How will this work with the ftrace?
> 

It won't affect ftrace, if that's the question you're asking.

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