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libsframe asan: avoid generating misaligned loads

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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.
This commit is contained in:
Indu Bhagat
2022-12-15 13:12:01 -08:00
parent 69de431392
commit 8c078abdc2
4 changed files with 42 additions and 24 deletions
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8
include/sframe-api.h
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@ -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)