[PATCH v4 02/13] buildid: Add API to parse build ID out of buffer

[Stephen Boyd]

Add an API that can parse the build ID out of a buffer, instead of a
vma, to support printing a kernel module's build ID for stack traces.

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>
Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
---
 include/linux/buildid.h |  1 +
 lib/buildid.c           | 50 ++++++++++++++++++++++++++++++-----------
 2 files changed, 38 insertions(+), 13 deletions(-)

diff --git a/include/linux/buildid.h b/include/linux/buildid.h
index 40232f90db6e..ebce93f26d06 100644
--- a/include/linux/buildid.h
+++ b/include/linux/buildid.h
@@ -8,5 +8,6 @@
 
 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);
 
 #endif
diff --git a/lib/buildid.c b/lib/buildid.c
index e014636ec3eb..6aea1c4e5e85 100644
--- a/lib/buildid.c
+++ b/lib/buildid.c
@@ -2,30 +2,23 @@
 
 #include <linux/buildid.h>
 #include <linux/elf.h>
+#include <linux/kernel.h>
 #include <linux/pagemap.h>
 
 #define BUILD_ID 3
+
 /*
  * Parse build id from the note segment. This logic can be shared between
  * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
  * identical.
  */
-static inline int parse_build_id(void *page_addr,
-				 unsigned char *build_id,
-				 __u32 *size,
-				 void *note_start,
-				 Elf32_Word note_size)
+static int parse_build_id_buf(unsigned char *build_id,
+			      __u32 *size,
+			      const void *note_start,
+			      Elf32_Word note_size)
 {
 	Elf32_Word note_offs = 0, new_offs;
 
-	/* check for overflow */
-	if (note_start < page_addr || note_start + note_size < note_start)
-		return -EINVAL;
-
-	/* only supports note that fits in the first page */
-	if (note_start + note_size > page_addr + PAGE_SIZE)
-		return -EINVAL;
-
 	while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
 		Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
 
@@ -50,9 +43,27 @@ static inline int parse_build_id(void *page_addr,
 			break;
 		note_offs = new_offs;
 	}
+
 	return -EINVAL;
 }
 
+static inline int parse_build_id(void *page_addr,
+				 unsigned char *build_id,
+				 __u32 *size,
+				 void *note_start,
+				 Elf32_Word note_size)
+{
+	/* check for overflow */
+	if (note_start < page_addr || note_start + note_size < note_start)
+		return -EINVAL;
+
+	/* only supports note that fits in the first page */
+	if (note_start + note_size > page_addr + PAGE_SIZE)
+		return -EINVAL;
+
+	return parse_build_id_buf(build_id, size, note_start, note_size);
+}
+
 /* Parse build ID from 32-bit ELF */
 static int get_build_id_32(void *page_addr, unsigned char *build_id,
 			   __u32 *size)
@@ -148,3 +159,16 @@ int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
 	put_page(page);
 	return ret;
 }
+
+/**
+ * build_id_parse_buf - Get build ID from a buffer
+ * @buf:      Elf note section(s) to parse
+ * @buf_size: Size of @buf in bytes
+ * @build_id: Build ID parsed from @buf, at least BUILD_ID_SIZE_MAX long
+ *
+ * Return: 0 on success, -EINVAL otherwise
+ */
+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);
+}
-- 
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