[HWASan] Save + print registers when tag mismatch occurs in AArch64.
Summary:
This change change the instrumentation to allow users to view the registers at the point at which tag mismatch occured. Most of the heavy lifting is done in the runtime library, where we save the registers to the stack and emit unwind information. This allows us to reduce the overhead, as very little additional work needs to be done in each __hwasan_check instance.
In this implementation, the fast path of __hwasan_check is unmodified. There are an additional 4 instructions (16B) emitted in the slow path in every __hwasan_check instance. This may increase binary size somewhat, but as most of the work is done in the runtime library, it's manageable.
The failure trace now contains a list of registers at the point of which the failure occured, in a format similar to that of Android's tombstones. It currently has the following format:
Registers where the failure occurred (pc 0x0055555561b4):
x0
0000000000000014 x1
0000007ffffff6c0 x2
1100007ffffff6d0 x3
12000056ffffe025
x4
0000007fff800000 x5
0000000000000014 x6
0000007fff800000 x7
0000000000000001
x8
12000056ffffe020 x9
0200007700000000 x10
0200007700000000 x11
0000000000000000
x12
0000007fffffdde0 x13
0000000000000000 x14
02b65b01f7a97490 x15
0000000000000000
x16
0000007fb77376b8 x17
0000000000000012 x18
0000007fb7ed6000 x19
0000005555556078
x20
0000007ffffff768 x21
0000007ffffff778 x22
0000000000000001 x23
0000000000000000
x24
0000000000000000 x25
0000000000000000 x26
0000000000000000 x27
0000000000000000
x28
0000000000000000 x29
0000007ffffff6f0 x30
00000055555561b4
... and prints after the dump of memory tags around the buggy address.
Every register is saved exactly as it was at the point where the tag mismatch occurs, with the exception of x16/x17. These registers are used in the tag mismatch calculation as scratch registers during __hwasan_check, and cannot be saved without affecting the fast path. As these registers are designated as scratch registers for linking, there should be no important information in them that could aid in debugging.
Reviewers: pcc, eugenis
Reviewed By: pcc, eugenis
Subscribers: srhines, kubamracek, mgorny, javed.absar, krytarowski, kristof.beyls, hiraditya, jdoerfert, llvm-commits, #sanitizers
Tags: #sanitizers, #llvm
Differential Revision: https://reviews.llvm.org/D58857
llvm-svn: 355738