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bug#16986: Fw: Re: Crash when idle
From: |
YAMAMOTO Mitsuharu |
Subject: |
bug#16986: Fw: Re: Crash when idle |
Date: |
Wed, 23 Jul 2014 19:09:50 +0900 |
User-agent: |
Wanderlust/2.14.0 (Africa) SEMI/1.14.6 (Maruoka) FLIM/1.14.8 (Shijō) APEL/10.6 Emacs/22.3 (sparc-sun-solaris2.8) MULE/5.0 (SAKAKI) |
>>>>> On Thu, 15 May 2014 09:31:32 +0100, Simon Carter <bbbscarter@gmail.com>
>>>>> said:
> 10 org.gnu.Emacs 0x00000001000d734a directory_files_internal + 742
> Dump of assembler code for function directory_files_internal:
> 0x00000001000d732a <+710>: callq 0x1000f4365 <make_uninit_multibyte_string>
> 0x00000001000d732f <+715>: mov %rax,-0x48(%rbp)
> 0x00000001000d7333 <+719>: mov 0x17(%rax),%rdi
> 0x00000001000d7337 <+723>: mov -0x88(%rbp),%rax
> 0x00000001000d733e <+730>: mov (%rax),%rsi
> 0x00000001000d7341 <+733>: mov -0x70(%rbp),%rdx
> 0x00000001000d7345 <+737>: callq 0x1001a1b08
> 0x00000001000d734a <+742>: mov -0x8c(%rbp),%eax
The above callq corresponds to the call to memcpy below:
276 memcpy (SDATA (fullname), SDATA (directory),
277 directory_nbytes);
The second argument is passed to memcpy via the register %rsi, which
is set to `(%rax)' at <+730>. Note that this is done *without
displacement* (compare it with the instruction for the first argument
%rdi at <+719>). That means the value of %rax at <+730> is
&XSTRING(directory)->data rather than `directory' itself, which seems
to be optimized out by the compiler possibly because SDATA(directory)
is used inside a loop and `directory' is not used later in the other
places.
As the following comment says, DECODE_FILE can GC in general:
251 /* Note: DECODE_FILE can GC; it should protect its argument,
252 though. */
253 name = DECODE_FILE (name);
254 len = SBYTES (name);
And actually the NS port on Darwin uses a special `utf-8-nfd' file
coding system that involves Lisp evaluation via the
`:post-read-conversion' property.
I suspect there are no direct references to the value of `directory'
from stack contents or register values, and thus GC triggered by the
above DECODE_FILE has collected the value of `directory' as a garbage.
If that is the case, %rax at <+730> (i.e., &XSTRING(directory)->data)
would become invalid.
YAMAMOTO Mitsuharu
mituharu@math.s.chiba-u.ac.jp
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