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Evan Jones

2005-Nov-23 03:04 UTC

[LLVMdev] llvm-ranlib: Bus Error in regressions + fix

On Nov 22, 2005, at 19:10, Reid Spencer wrote:> 1. What is the path name associated with TmpArchive? If its the same 
> as the path name associated with archPath then that's a bug, probably 
> introduced when Path::makeUnique is called from 
> Path::createTemporaryFileOnDisk which is called from line 377 of 
> ArchiveWriter.cpp.
This does not appear to be the problem. I excluded the lines from the 
strace that created this temporary file. After line 377:

(gdb) p TmpArchive
$2 = {path = {static npos = 4294967295,
     _M_dataplus = {<allocator<char>> = {<No data fields>},
       _M_p = 0x835407c "temp.GNU.a-PozKFJ"}, static 
_S_empty_rep_storage = {0,
       0, 4, 0}}}
(gdb) p archPath
$3 = {path = {static npos = 4294967295,
     _M_dataplus = {<allocator<char>> = {<No data fields>},
       _M_p = 0x83545f4 "temp.GNU.a5\b"}, static _S_empty_rep_storage
=
{0, 0,
       4, 0}}}

So these two variables are pointing to different files, and the 
creation of TmpArchive works just fine.  The strace including the parts 
that reference the temporary file is appended to the end of the email. 
The very last open to the "archPath" file is at line 429, where it 
truncates it even though the foreignST pointer refers to data mmaped in 
that file. Is this data supposed to be copied out of the original file, 
or is another temporary supposed to be created and then the original 
could be replaced using a file move operation instead?

I'll try this on my Debian unstable system tomorrow. If ranlib works 
there, maybe I can track down the difference.

Evan Jones


open("temp.GNU.a", O_RDONLY)            = 3
fstat64(3, {st_mode=S_IFREG|0600, st_size=4210, ...}) = 0
mmap2(NULL, 8192, PROT_READ, MAP_PRIVATE, 3, 0) = 0x40017000
gettimeofday({1132714484, 283020}, NULL) = 0
getpid()                                = 28656
open("temp.GNU.a-O1Q6E8", O_RDWR|O_CREAT|O_EXCL, 0600) = 4
close(4)                                = 0
open("temp.GNU.a-O1Q6E8", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 4
close(4)                                = 0

*** SIGNAL HANDLING REMOVED ***

open("temp.GNU.a-O1Q6E8", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 4
brk(0)                                  = 0x8357000
brk(0x8359000)                          = 0x8359000
fstat64(4, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 
0) = 0x40019000
_llseek(4, 0, [0], SEEK_CUR)            = 0
_llseek(4, 0, [0], SEEK_SET)            = 0
_llseek(4, 0, [0], SEEK_SET)            = 0
_llseek(4, 0, [0], SEEK_SET)            = 0
_llseek(4, 0, [0], SEEK_SET)            = 0
brk(0)                                  = 0x8359000
brk(0x8369000)                          = 0x8369000
brk(0)                                  = 0x8369000
brk(0x836a000)                          = 0x836a000
mmap2(NULL, 2002944, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 
-1, 0) = 0x4013b000
munmap(0x4013b000, 2002944)             = 0
_llseek(4, 0, [0], SEEK_SET)            = 0
_llseek(4, 0, [0], SEEK_SET)            = 0
_llseek(4, 0, [0], SEEK_SET)            = 0
write(4, "!<arch>\nevenlen/        11008330"..., 4040) = 4040
close(4)                                = 0
munmap(0x40019000, 4096)                = 0
access("temp.GNU.a-O1Q6E8", F_OK)       = 0
open("temp.GNU.a-O1Q6E8", O_RDONLY)     = 4
fstat64(4, {st_mode=S_IFREG|0600, st_size=4040, ...}) = 0
mmap2(NULL, 4096, PROT_READ, MAP_PRIVATE, 4, 0) = 0x40019000
open("temp.GNU.a", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 5
fstat64(5, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 
0) = 0x4001a000
_llseek(5, 0, [0], SEEK_CUR)            = 0
--- SIGBUS (Bus error) @ 0 (0) ---


--
Evan Jones
http://evanjones.ca/

Reid Spencer

2005-Nov-23 04:59 UTC

head link

[LLVMdev] llvm-ranlib: Bus Error in regressions + fix

Evan Jones wrote:
> On Nov 22, 2005, at 19:10, Reid Spencer wrote:
> 
>> 1. What is the path name associated with TmpArchive? If its the same 
>> as the path name associated with archPath then that's a bug,
probably
>> introduced when Path::makeUnique is called from 
>> Path::createTemporaryFileOnDisk which is called from line 377 of 
>> ArchiveWriter.cpp.
> 
> 
> This does not appear to be the problem. I excluded the lines from the 
> strace that created this temporary file. After line 377:
> 
> (gdb) p TmpArchive
> $2 = {path = {static npos = 4294967295,
>     _M_dataplus = {<allocator<char>> = {<No data
fields>},
>       _M_p = 0x835407c "temp.GNU.a-PozKFJ"}, static
_S_empty_rep_storage
That looks like mkstemp working correctly.
> = {0,
>       0, 4, 0}}}
> (gdb) p archPath
> $3 = {path = {static npos = 4294967295,
>     _M_dataplus = {<allocator<char>> = {<No data
fields>},
>       _M_p = 0x83545f4 "temp.GNU.a5\b"}, static
_S_empty_rep_storage =
What's with the "5\b" at the end? Looks like garbage to me. Not
sure what's up
with that.> {0, 0,
>       4, 0}}}
> 
> So these two variables are pointing to different files, and the creation 
> of TmpArchive works just fine.  The strace including the parts that 
> reference the temporary file is appended to the end of the email. 
Okay, the previous strace looked like they were both opening
"temp.GNU.a";
perhaps the names were truncated in the strace.  Anyway, you're right, this 
isn't the problem if the file names are different.
> The 
> very last open to the "archPath" file is at line 429, where it
truncates
> it even though the foreignST pointer refers to data mmaped in that file. 
Yes, the foreignST points to a non-LLVM symbol table which must be retained for 
compatibility with other AR implementations. Unfortunately, it is being held 
from a file that is about to be mmap'd.
> Is this data supposed to be copied out of the original file, 
That's one solution but it defeats the purpose/efficiency of the mmap.

or is> another temporary supposed to be created and then the original could be 
> replaced using a file move operation instead?
Another temporary file would be even slower than copying the memory in
memory.> 
> I'll try this on my Debian unstable system tomorrow. If ranlib works 
> there, maybe I can track down the difference.
Sounds like a plan. Its a bit difficult to debug this over email. If you get 
stuck, let me know and I'll gen up a debug environment to take a look at it.
Chances are, however, that I won't be able to replicate this problem on FC3 
since it passes the nightly test here.
>   > open("temp.GNU.a", O_RDONLY)            = 3

Original file being opened (read-only, because we're not supposed to modify
it)
> fstat64(3, {st_mode=S_IFREG|0600, st_size=4210, ...}) = 0
> mmap2(NULL, 8192, PROT_READ, MAP_PRIVATE, 3, 0) = 0x40017000
> gettimeofday({1132714484, 283020}, NULL) = 0
> getpid()                                = 28656
> open("temp.GNU.a-O1Q6E8", O_RDWR|O_CREAT|O_EXCL, 0600) = 4
The temporary file that will contain the symbol table> close(4)                                = 0
> open("temp.GNU.a-O1Q6E8", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 4
> close(4)                                = 0Not sure why this is opened twice .. probably an llvm::sys::Path
issue.> 
> *** SIGNAL HANDLING REMOVED ***
> 
> open("temp.GNU.a-O1Q6E8", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 4Open yet again the temnporary file into which we'll build the
symtab.> brk(0)                                  = 0x8357000
> brk(0x8359000)                          = 0x8359000
> fstat64(4, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 
> 0) = 0x40019000
This mmap is just allocating memory> _llseek(4, 0, [0], SEEK_CUR)            = 0
> _llseek(4, 0, [0], SEEK_SET)            = 0
> _llseek(4, 0, [0], SEEK_SET)            = 0
> _llseek(4, 0, [0], SEEK_SET)            = 0
> _llseek(4, 0, [0], SEEK_SET)            = 0
> brk(0)                                  = 0x8359000
> brk(0x8369000)                          = 0x8369000
> brk(0)                                  = 0x8369000
> brk(0x836a000)                          = 0x836a000
> mmap2(NULL, 2002944, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 
> -1, 0) = 0x4013b000
more memory allocations> munmap(0x4013b000, 2002944)             = 0
> _llseek(4, 0, [0], SEEK_SET)            = 0
> _llseek(4, 0, [0], SEEK_SET)            = 0
> _llseek(4, 0, [0], SEEK_SET)            = 0
> write(4, "!<arch>\nevenlen/        11008330"..., 4040) =
4040
> close(4)                                = 0
> munmap(0x40019000, 4096)                = 0
> access("temp.GNU.a-O1Q6E8", F_OK)       = 0
> open("temp.GNU.a-O1Q6E8", O_RDONLY)     = 4
> fstat64(4, {st_mode=S_IFREG|0600, st_size=4040, ...}) = 0
> mmap2(NULL, 4096, PROT_READ, MAP_PRIVATE, 4, 0) = 0x40019000
map in the contents of the file we wrote.> open("temp.GNU.a", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 5
wipe out the original file> fstat64(5, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 
> 0) = 0x4001a000
allocate memory> _llseek(5, 0, [0], SEEK_CUR)            = 0
> --- SIGBUS (Bus error) @ 0 (0) ---
 From this strace it looks to me like the only solution is to copy the data 
pointed to by foreignST into malloc'd space. Its just a symbol table so it 
shouldn't be too huge.  The problem, as you've noted, is that the
foreignST
pointer is pointing into file handle 3. When file handle 5 is opened, the 
O_TRUNC parameter causes the memory pointed to by foreignST to be invalidated 
(unmapped). When we try to read this data in order to write it back to 
temp.GNU.a, it is getting the bus error trying to access the foreignST data.

There's two solutions:
(1) copy the data pointed to by foreignST
(2) build the new file with the symbol table in a 3rd temporary file which is 
later renamed as the original (temp.GNU.a in this case).


Reid.

Evan Jones

2005-Nov-23 13:16 UTC

head link

[LLVMdev] llvm-ranlib: Bus Error in regressions + fix

On Nov 22, 2005, at 23:59, Reid Spencer wrote:>> = {0,
>>       0, 4, 0}}}
>> (gdb) p archPath
>> $3 = {path = {static npos = 4294967295,
>>     _M_dataplus = {<allocator<char>> = {<No data
fields>},
>>       _M_p = 0x83545f4 "temp.GNU.a5\b"}, static
_S_empty_rep_storage > What's with the "5\b" at the end? Looks
like garbage to me. Not sure
> what's up with that.
The implementation of std::string on this system does not always NULL 
terminate strings. I verified that the path.length() value in that case 
was 10, and calling path.c_str() returned the correct NULL terminated 
string.


I found a system where llvm-ranlib "works," and I have figured out the
problem. Here is the crashed strace, after it opens the file:

open("temp.GNU.a", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 15
fstat64(15, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 
0) = 0x4001a000
_llseek(15, 0, [0], SEEK_CUR)           = 0
--- SIGBUS (Bus error) @ 0 (0) ---


and here is the "working" strace, after it opens the file:

open("temp.GNU.a", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 17
write(17, "!<arch>\n", 8)               = 8
_llseek(17, 0, [8], SEEK_CUR)           = 0
write(17, "/               1100833490  0   "..., 106) = 106
_llseek(17, 0, [114], SEEK_CUR)         = 0


Note that in the "working" case, the C++ library decides to flush the 
magic number to the file immediately. This causes the first page in the 
MMAPed file to be allocated (with zeros). Hence, when we go to read the 
foreignST pointer, it doesn't crash, but it has silently corrupted the 
data. The foreignST pointer looks like this when it is first read from 
the file:

(gdb) x/46bx foreignST->getData()
0xf6ffe044:     0x00    0x00    0x00    0x02    0x00    0x00    0x07    
0x4e
0xf6ffe04c:     0x00    0x00    0x07    0x4e    0x5f    0x5a    0x4e    
0x34
0xf6ffe054:     0x6c    0x6c    0x76    0x6d    0x35    0x49    0x73    
0x4e
0xf6ffe05c:     0x41    0x4e    0x45    0x66    0x00    0x5f    0x5a    
0x4e
0xf6ffe064:     0x34    0x6c    0x6c    0x76    0x6d    0x35    0x49    
0x73
0xf6ffe06c:     0x4e    0x41    0x4e    0x45    0x64    0x00


And it looks like this just before it gets written out:

(gdb) x/46bx foreignST->getData()
0xf6ffe044:     0x00    0x00    0x00    0x00    0x00    0x00    0x00    
0x00
0xf6ffe04c:     0x00    0x00    0x00    0x00    0x00    0x00    0x00    
0x00
0xf6ffe054:     0x00    0x00    0x00    0x00    0x00    0x00    0x00    
0x00
0xf6ffe05c:     0x00    0x00    0x00    0x00    0x00    0x00    0x00    
0x00
0xf6ffe064:     0x00    0x00    0x00    0x00    0x00    0x00    0x00    
0x00
0xf6ffe06c:     0x00    0x00    0x00    0x00    0x00    0x00


You can tell that it is getting corrupted by looking at the file with 
"hexdump -C" before and after llvm-ranlib. The native symbol table is 
supposed to start at offset 0x44.

>> Is this data supposed to be copied out of the original file,
> That's one solution but it defeats the purpose/efficiency of the mmap.
Well, only the native symbol table would need to be copied, and only in 
the writeToDisk function, before the file gets invalidated.

>> another temporary supposed to be created and then the original could 
>> be replaced using a file move operation instead?
> Another temporary file would be even slower than copying the memory in 
> memory.
I'm not so sure about that. The archive file is being truncated anyway. 
How much worse would it be to unlink the file before writing it out? 
The operating system probably already deallocates the disk blocks as 
soon as it is truncated. That also fixes the problem, since the 
original mapped file still exists until it is unmapped.

> There's two solutions:
> (1) copy the data pointed to by foreignST
> (2) build the new file with the symbol table in a 3rd temporary file 
> which is later renamed as the original (temp.GNU.a in this case).
(3) unlink the original file first (basically equivalent to (2))
(4) Write the foreignST into the TmpArchive file. Is there any reason 
that this isn't possible? Then the final archive would be created in a 
single pass, and it could just be moved into place.

Also, since writeToDisk() invalidates the mapped file that was 
originally used to create the archive, shouldn't this function also 
unmap that file and erase all its members? This would prevent and 
further bugs like this from happening.

Evan Jones

--
Evan Jones
http://evanjones.ca/

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