[PATCH v4 03/13] buildid: Stash away kernels build ID on init

[Stephen Boyd]

Parse the kernel's build ID at initialization so that other code 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@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Jessica Yu <jeyu@xxxxxxxxxx>
Cc: Evan Green <evgreen@xxxxxxxxxxxx>
Cc: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: <kexec@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
---
 include/linux/buildid.h |  3 +++
 init/main.c             |  1 +
 lib/buildid.c           | 15 +++++++++++++++
 3 files changed, 19 insertions(+)

diff --git a/include/linux/buildid.h b/include/linux/buildid.h
index ebce93f26d06..f375900cf9ed 100644
--- a/include/linux/buildid.h
+++ b/include/linux/buildid.h
@@ -10,4 +10,7 @@ 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);
 
+extern unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX];
+void init_vmlinux_build_id(void);
+
 #endif
diff --git a/init/main.c b/init/main.c
index 53b278845b88..eaede2f41327 100644
--- a/init/main.c
+++ b/init/main.c
@@ -857,6 +857,7 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
 	set_task_stack_end_magic(&init_task);
 	smp_setup_processor_id();
 	debug_objects_early_init();
+	init_vmlinux_build_id();
 
 	cgroup_init_early();
 
diff --git a/lib/buildid.c b/lib/buildid.c
index 6aea1c4e5e85..1103ed46214f 100644
--- a/lib/buildid.c
+++ b/lib/buildid.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include <linux/buildid.h>
+#include <linux/cache.h>
 #include <linux/elf.h>
 #include <linux/kernel.h>
 #include <linux/pagemap.h>
@@ -172,3 +173,17 @@ 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);
 }
+
+unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX] __ro_after_init;
+
+/**
+ * init_vmlinux_build_id - Compute and stash the running kernel's build ID
+ */
+void __init init_vmlinux_build_id(void)
+{
+	extern const void __start_notes __weak;
+	extern const void __stop_notes __weak;
+	unsigned int size = &__stop_notes - &__start_notes;
+
+	build_id_parse_buf(&__start_notes, vmlinux_build_id, size);
+}
-- 
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