String segfault with wide character function, Windows

Ruby
1

Ruby 1.8.4 (one click)
Windows XP

Check this out segfault:

strtest.rb

require ‘Win32API’

GetFullPathNameW = Win32API.new(‘kernel32’,‘GetFullPathNameW’,‘PLPP’,
‘L’)

path = “C:\test”
buf = 0.chr * 260

if GetFullPathNameW.call(path, buf.size, buf, 0) == 0
puts “Failed”
end

#p buf
p buf.split("\0\0").first # boom!

Result

strtest.rb:13: [BUG] Segmentation fault
ruby 1.8.4 (2005-12-24) [i386-mswin32]

This application has requested the Runtime to terminate it in an unusual
way. Please contact the application’s support team for more information.

I noticed that if I dropped the ‘buf’ to 245 or fewer characters, it
works ok. Also, it segfaults on just about any op that modifies buf,
not just String#split.

Any ideas?

Thanks,

Dan

2

Daniel B. wrote:

path = “C:\test”
strtest.rb:13: [BUG] Segmentation fault

Thanks,

Dan

The solution was found by Heesob, which I have pasted below (taken from
the win32utils-devel mailing list):

I have found out what is the problem.
It’s not bug of Ruby or Windows, it is only bug of code.

First try this:

require ‘Win32API’
GetFullPathNameW = Win32API.new(‘kernel32’,‘GetFullPathNameW’,‘PLPP’,
‘L’)
for i in 1…100
path = “c:\test”
buf = 0.chr * 260
if GetFullPathNameW.call(path, buf.size, buf, 0) == 0
puts “Failed”
end
p buf.split("\0\0").first
end

It will cause various errors like
uninitialized constant GetFullPathNameW (NameError)
or
segfault.

Next, try this:

require ‘Win32API’
GetFullPathNameW = Win32API.new(‘kernel32’,‘GetFullPathNameW’,‘PLPP’,
‘L’)
for i in 1…100
path = “c:\test”
buf = 0.chr * 260

buf.size/2 -> actual length of buf

if GetFullPathNameW.call(path, buf.size/2, buf, 0) == 0
puts “Failed”
end
p buf.split("\0\0").first
end

It runs Ok. but the result is not correct.

Next , try this:

require ‘Win32API’
GetFullPathNameW = Win32API.new(‘kernel32’,‘GetFullPathNameW’,‘PLPP’,
‘L’)
for i in 1…100

append \0 to path

path = “c:\test\0”
buf = 0.chr * 260

buf.size/2 -> actual length of buf in unicode string

if GetFullPathNameW.call(path, buf.size/2, buf, 0) == 0
puts “Failed”
end
p buf.split("\0\0").first
end

It runs ok. The result is correct.

Finally, the complete and correct code is like this:

require ‘Win32API’
GetFullPathNameW = Win32API.new(‘kernel32’,‘GetFullPathNameW’,‘PLPP’,
‘L’)
for i in 1…100
path = “c\0:\0\\0t\0e\0s\0t\0\0”
buf = 0.chr * 260

buf.size/2 -> actual length of buf in unicode string

if GetFullPathNameW.call(path, buf.size/2, buf, 0) == 0
puts “Failed”
end
buf = buf.split("\0\0").first
buf = (buf.size % 2).zero? ? buf : buf+"\0"
p buf
end

Remeber, Ruby’s string is terminated with “\0” implicitly, but UTF16
string requires double “\0”.
For ascii chars, it happens trailing three “\0” : one for ascii char
and two for string termination.

Regards,

Park H.