[lttng-dev] lttng-consumerd crash on aarch64 due to x86 arch specific optimization

[Anders Wallin]

Hi,

architectures that has memory alignment restrictions may/will fail with the
optimization done in 51b8f2fa2b972e62117caa946dd3e3565b6ca4a3.
Please revert the patch or make it X86 specific.

Regards

Anders Wallin

------------------------------------------------------------------------------------------------------------
commit 51b8f2fa2b972e62117caa946dd3e3565b6ca4a3
Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
Date:   Sun Sep 25 12:31:11 2016 -0400

    Performance: implement lttng_inline_memcpy

    Because all length parameters received for serializing data coming from
    applications go through a callback, they are never constant, and it
    hurts performance to perform a call to memcpy each time.

    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>

diff --git a/libringbuffer/backend_internal.h
b/libringbuffer/backend_internal.h
index 90088b89..e597cf4d 100644
--- a/libringbuffer/backend_internal.h
+++ b/libringbuffer/backend_internal.h
@@ -592,6 +592,28 @@ int update_read_sb_index(const struct
lttng_ust_lib_ring_buffer_config *config,
 #define inline_memcpy(dest, src, n)    memcpy(dest, src, n)
 #endif

+static inline __attribute__((always_inline))
+void lttng_inline_memcpy(void *dest, const void *src,
+               unsigned long len)
+{
+       switch (len) {
+       case 1:
+               *(uint8_t *) dest = *(const uint8_t *) src;
+               break;
+       case 2:
+               *(uint16_t *) dest = *(const uint16_t *) src;
+               break;
+       case 4:
+               *(uint32_t *) dest = *(const uint32_t *) src;
+               break;
+       case 8:
+               *(uint64_t *) dest = *(const uint64_t *) src;
+               break;
+       default:
+               inline_memcpy(dest, src, len);
+       }
+}
+
 /*
  * Use the architecture-specific memcpy implementation for constant-sized
  * inputs, but rely on an inline memcpy for length statically unknown.
@@ -603,7 +625,7 @@ do {
            \
        if (__builtin_constant_p(len))                          \
                memcpy(dest, src, __len);                       \
        else                                                    \
-               inline_memcpy(dest, src, __len);                \
+               lttng_inline_memcpy(dest, src, __len);          \
 } while (0)

 /*

----------------------------------------------------------------------------------------------------
Here is one example of a crash, where 0xf3b7eeb2 is not 8 byte aligned;

  (gdb) bt full
#0  lttng_inline_memcpy (len=8, src=0xf3b7eeb2, dest=<optimized out>) at
/usr/src/debug/lttng-ust/2.9.1/git/libringbuffer/backend_internal.h:610
No locals.
#1  lib_ring_buffer_write (len=8, src=0xf3b7eeb2, ctx=0xf57c47d0,
config=0xf737c560 <client_config>) at
/usr/src/debug/lttng-ust/2.9.1/git/libringbuffer/backend.h:100
        __len = 8
        handle = 0xf3b2e0c0
        backend_pages = <optimized out>
        chanb = 0xf3b2e2e0
        offset = <optimized out>
#2  lttng_event_write (ctx=0xf57c47d0, src=0xf3b7eeb2, len=8) at
/usr/src/debug/lttng-ust/2.9.1/git/liblttng-ust/lttng-ring-buffer-metadata-client.h:267
No locals.
#3  0xf7337ef8 in ustctl_write_one_packet_to_channel (channel=<optimized
out>, metadata_str=0xf3b7eeb2 "", len=<optimized out>) at
/usr/src/debug/lttng-ust/2.9.1/git/liblttng-ust-ctl/ustctl.c:1183
        ctx = {chan = 0xf3b2e290, priv = 0x0, handle = 0xf3b2e0c0,
data_size = 8, largest_align = 1, cpu = -1, buf = 0xf6909000, slot_size =
8, buf_offset = 163877, pre_offset = 163877, tsc = 0, rflags = 0, ctx_len =
80, ip = 0x0, priv2 = 0x0, padding2 = '\000' <repeats 11 times>,
backend_pages = 0xf690c000}
        chan = 0xf3b2e4d8
        str = 0xf3b7eeb2 ""
        reserve_len = 8
        ret = <optimized out>
        __func__ = '\000' <repeats 34 times>
        __PRETTY_FUNCTION__ = '\000' <repeats 34 times>
---Type <return> to continue, or q <return> to quit---
#4  0x000344cc in commit_one_metadata_packet (stream=stream at entry=0xf3b2e560)
at ust-consumer.c:2206
        write_len = <optimized out>
        ret = <optimized out>
        __PRETTY_FUNCTION__ = "commit_one_metadata_packet"
#5  0x00036538 in lttng_ustconsumer_read_subbuffer
(stream=stream at entry=0xf3b2e560,
ctx=ctx at entry=0x25e6e8) at ust-consumer.c:2452
        len = 4096
        subbuf_size = 4093
        padding = <optimized out>
        err = -11
        write_index = 1
        ret = <optimized out>
        ustream = <optimized out>
        index = {offset = 0, packet_size = 575697416355872, content_size =
17564043391468256584, timestamp_begin = 17564043425827782792, timestamp_end
= 34359738496, events_discarded = 313327092840, stream_id = 4089446416,
stream_instance_id = 17689097291346376608, packet_seq_num = 8589934593}
        __PRETTY_FUNCTION__ = "lttng_ustconsumer_read_subbuffer"
        __func__ = "lttng_ustconsumer_read_subbuffer"
.....
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