lttng team mailing list archive

[Colin King <1316617@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

Decoding an lttng user space trace on an ARM platform results in a bus
error.    Gdb shows this to be:

0x4004358c in yyparse (scanner=0x19fe0, yyscanner=0x199f0)
    at ctf-parser.y:1210
1210                            $$->u.unary_expression.u.unsigned_constant = $1;
(gdb) where
#0  0x4004358c in yyparse (scanner=0x19fe0, yyscanner=0x199f0)
    at ctf-parser.y:1210
#1  0x400380ca in ctf_trace_metadata_read (td=td@entry=0x1a600,
    metadata_fp=metadata_fp@entry=0x0, scanner=0x19fe0, append=append@entry=0)
    at ctf.c:1281
#2  0x40039d38 in ctf_open_trace_read (metadata_fp=0x0,
    packet_seek=0x40039295 <ctf_packet_seek>, flags=0,
    path=0x19ab0 "/home/phablet/lttng-traces/auto-20130101-023753/ust/uid/0/32-bit", td=0x1a600) at ctf.c:2111
#3  ctf_open_trace (
    path=0x19ab0 "/home/phablet/lttng-traces/auto-20130101-023753/ust/uid/0/32-bit", flags=0, packet_seek=0x40039295 <ctf_packet_seek>, metadata_fp=0x0)
    at ctf.c:2206
#4  0x400242f8 in bt_context_add_trace (ctx=ctx@entry=0x15f30,
    path=0x19ab0 "/home/phablet/lttng-traces/auto-20130101-023753/ust/uid/0/32-bit", format_name=format_name@entry=0x15ff0 "ctf",
    packet_seek=packet_seek@entry=0x0, stream_list=stream_list@entry=0x0,
    metadata=metadata@entry=0x0) at context.c:95
#5  0x0000a7d2 in bt_context_add_traces_recursive (ctx=ctx@entry=0x15f30,
    path=path@entry=0x18968 "/home/phablet/lttng-traces/auto-20130101-023753", format_str=0x15ff0 "ctf", packet_seek=packet_seek@entry=0x0)
    at babeltrace.c:529
#6  0x00009c86 in main (argc=<optimized out>, argv=<optimized out>)

A workaround is to enable misaligned access handling in the kernel:

echo 2 | sudo tee /proc/cpu/alignment

Alternatively,  making struct ctf_node in formats/ctf/metadata/ctf-ast.h
packed using the gcc attribute __attribute__((packed())) seems to stop
this.

I think this is reported upstream too: https://bugs.lttng.org/issues/789

** Affects: babeltrace (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1316617

Title:
  babeltrace unaligned access bus errors

Status in “babeltrace” package in Ubuntu:
  New

Bug description:
  Decoding an lttng user space trace on an ARM platform results in a bus
  error.    Gdb shows this to be:

  0x4004358c in yyparse (scanner=0x19fe0, yyscanner=0x199f0)
      at ctf-parser.y:1210
  1210                            $$->u.unary_expression.u.unsigned_constant = $1;
  (gdb) where
  #0  0x4004358c in yyparse (scanner=0x19fe0, yyscanner=0x199f0)
      at ctf-parser.y:1210
  #1  0x400380ca in ctf_trace_metadata_read (td=td@entry=0x1a600,
      metadata_fp=metadata_fp@entry=0x0, scanner=0x19fe0, append=append@entry=0)
      at ctf.c:1281
  #2  0x40039d38 in ctf_open_trace_read (metadata_fp=0x0,
      packet_seek=0x40039295 <ctf_packet_seek>, flags=0,
      path=0x19ab0 "/home/phablet/lttng-traces/auto-20130101-023753/ust/uid/0/32-bit", td=0x1a600) at ctf.c:2111
  #3  ctf_open_trace (
      path=0x19ab0 "/home/phablet/lttng-traces/auto-20130101-023753/ust/uid/0/32-bit", flags=0, packet_seek=0x40039295 <ctf_packet_seek>, metadata_fp=0x0)
      at ctf.c:2206
  #4  0x400242f8 in bt_context_add_trace (ctx=ctx@entry=0x15f30,
      path=0x19ab0 "/home/phablet/lttng-traces/auto-20130101-023753/ust/uid/0/32-bit", format_name=format_name@entry=0x15ff0 "ctf",
      packet_seek=packet_seek@entry=0x0, stream_list=stream_list@entry=0x0,
      metadata=metadata@entry=0x0) at context.c:95
  #5  0x0000a7d2 in bt_context_add_traces_recursive (ctx=ctx@entry=0x15f30,
      path=path@entry=0x18968 "/home/phablet/lttng-traces/auto-20130101-023753", format_str=0x15ff0 "ctf", packet_seek=packet_seek@entry=0x0)
      at babeltrace.c:529
  #6  0x00009c86 in main (argc=<optimized out>, argv=<optimized out>)

  A workaround is to enable misaligned access handling in the kernel:

  echo 2 | sudo tee /proc/cpu/alignment

  Alternatively,  making struct ctf_node in formats/ctf/metadata/ctf-
  ast.h packed using the gcc attribute __attribute__((packed())) seems
  to stop this.

  I think this is reported upstream too:
  https://bugs.lttng.org/issues/789

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