libsframe asan: avoid generating misaligned loads

There are two places where unaligned loads were seen on aarch64:
  - #1. access to the SFrame FRE stack offsets in the in-memory
    representation/abstraction provided by libsframe.
  - #2. access to the SFrame FRE start address in the on-disk representation
    of the frame row entry.

For #1, we can fix this by reordering the struct members of
sframe_frame_row_entry in libsframe/sframe-api.h.

For #2, we need to default to using memcpy instead, and copy out the bytes
to a location for output.

SFrame format is an unaligned on-disk format. As such, there are other blobs
of memory in the on-disk SFrame FRE that are on not on their natural
boundaries.  But that does not pose further problems yet, because the users
are provided access to the on-disk SFrame FRE data via libsframe's
sframe_frame_row_entry, the latter has its' struct members aligned on their
respective natural boundaries (and initialized using memcpy).

PR 29856 libsframe asan: load misaligned at sframe.c:516

ChangeLog:

	PR libsframe/29856
	* bfd/elf64-x86-64.c: Adjust as the struct members have been
	reordered.
	* libsframe/sframe.c (sframe_decode_fre_start_address): Use
	memcpy to perform 16-bit/32-bit reads.
	* libsframe/testsuite/libsframe.encode/encode-1.c: Adjust as the
	struct members have been reordered.

include/ChangeLog:

	PR libsframe/29856
	* sframe-api.h: Reorder fre_offsets for natural alignment.

1 files changed, 6 insertions, 2 deletions

diff --git a/include/sframe-api.h b/include/sframe-api.h
index 0a86389..c9db39e 100644
--- a/include/sframe-api.h
+++ b/include/sframe-api.h
@@ -34,13 +34,17 @@ typedef struct sframe_encoder_ctx sframe_encoder_ctx;
 
 /* User interfacing SFrame Row Entry.
    An abstraction provided by libsframe so the consumer is decoupled from
-   the binary format representation of the same.  */
+   the binary format representation of the same.
+
+   The members are best ordered such that they are aligned at their natural
+   boundaries.  This helps avoid usage of undesirable misaligned memory
+   accesses.  See PR libsframe/29856.  */
 
 typedef struct sframe_frame_row_entry
 {
   uint32_t fre_start_addr;
-  unsigned char fre_info;
   unsigned char fre_offsets[MAX_OFFSET_BYTES];
+  unsigned char fre_info;
 } sframe_frame_row_entry;
 
 #define SFRAME_ERR ((int) -1)