I am trying to rebuild the 2.7 maintenance branch and get this error
on Ubuntu 10.04.1 LTS:

XXX lineno: 743, opcode: 0
Traceback (most recent call last):
 File "/usr/local/src/python-2.7-maint-svn/Lib/site.py", line 62, in <module>
  import os
 File "/usr/local/src/python-2.7-maint-svn/Lib/os.py", line 743, in <module>
  def urandom(n):
SystemError: unknown opcode

I installed it successfully once so I may be getting conflicts, but I can't figure out why.  There were some similar bugs reported in previous versions but I didn't see a clear solution.

I have done "make distclean" and "./configure".  I have unset my
PYTHONPATH and LD_LIBRARY_PATH, but python2.7 is my default python from a previous good build and installation.

Maybe a corrupted .pyc file? Can you please attach the file
/usr/local/src/python-2.7-maint-svn/Lib/os.pyc

File attached as requested.

Note that I tried to reproduce this on my 10.04.1 system, with various states of Python 2.7 installed, etc. and was unable to reproduce it.  It's certainly odd that you're getting the SystemError on that line.

For some reason your file os.pyc is corrupted:
I loaded it with a working python2.7:

import marshal, dis
pyc = open('bados.pyc', 'rb').read()
code = marshal.loads(pyc[8:])
dis.dis(code)

And it appears that all the "jump" instructions are wrong: the address is either 0, or something around 65536.

Which compiler do you use? I remember subtle bugs caused by some version of gcc.

I'm using gcc-4.5.1.  I'll try an older version: gcc (Ubuntu 4.4.3-4ubuntu5) 4.4.3.

The build succeeded with the older version of gcc.  I either have a mis-compiled gcc-4.5.1 (but the same version on another host worked okay) or gcc has a very subtle bug.  I think this issue can be considered closed; however, it may be worth a note in a FAQ or build instructions.  Good catch Amaury!

Correction on the bad gcc compiler: the actual version was a non-released version off the gcc-4.6 branch:  gcc version 4.6.0 20100908 (experimental) (GCC).  I'm filing a bug with gcc.  Sorry for the wasted time.

You're welcome.
Please join a link to the gcc bug when you have one.

Here is a link to the thread I started on the gcc-help mailing list concerning the issue: 

  http://gcc.gnu.org/ml/gcc-help/2010-09/msg00170.html

If I don't get a successful build with the current gcc trunk, I imagine this thread will transfer to the gcc (dev) list--I'll try to keep the links up.

I'm getting no interest from the gcc group at the moment.  I would like to help track down the bug and will nose around the Python source to zero in on where the problem is for detailed debugging.  Can anyone point me to the key files that concern the byte compiler?

You can look at Python/compile.c (the ast-to-bytecode compiler), Python/peephole.c (the bytecode optimizer), Python/marshal.c (the on-disk bytecode serializer/unserialize).

First step could be to actually disable the optimizer (see PyCode_Optimize in peephole.c).

I narrowed this issue down to -ftree-vectorize, which is part of
-O3.

With gcc-4.6 -O1, Python 3.2 works correctly. With gcc-4.6 -O1 -ftree-vectorize, the assertion "assert (new_line - last_line < 255);" fails in PyCode_Optimize().

I think that the problem is in the following loop:
-------------------------------------
#define NOP    9
#define HAVE_ARGUMENT  90  /* Opcodes from here have an argument: */
#define HAS_ARG(op) ((op) >= HAVE_ARGUMENT)
#define CODESIZE(op)  (HAS_ARG(op) ? 3 : 1)

unsigned char *codestr = NULL;
Py_ssize_t codelen;
int *addrmap = NULL;

/* Fixup linenotab */
for (i=0, nops=0 ; i<codelen ; i += CODESIZE(codestr[i])) {
    addrmap[i] = i - nops;
    if (codestr[i] == NOP)
        nops++;
}
-------------------------------------

gcc-4.6 -O1:
-------------------------------------
0x0000000000480991 <+5041>:  mov    %eax,%edx
0x0000000000480993 <+5043>:  sub    %esi,%edx
0x0000000000480995 <+5045>:  mov    %edx,(%r12,%rax,4)
0x0000000000480999 <+5049>:  movzbl 0x0(%rbp,%rax,1),%edx
0x000000000048099e <+5054>:  cmp    $0x9,%dl
0x00000000004809a1 <+5057>:  jne    0x4809a8 <PyCode_Optimize+5064>
0x00000000004809a3 <+5059>:  add    $0x1,%esi
0x00000000004809a6 <+5062>:  jmp    0x4809b2 <PyCode_Optimize+5074>
0x00000000004809a8 <+5064>:  mov    $0x3,%ecx
0x00000000004809ad <+5069>:  cmp    $0x59,%dl
0x00000000004809b0 <+5072>:  ja     0x4809b7 <PyCode_Optimize+5079>
0x00000000004809b2 <+5074>:  mov    $0x1,%ecx
0x00000000004809b7 <+5079>:  add    %rcx,%rax
0x00000000004809ba <+5082>:  cmp    %rax,%rdi
0x00000000004809bd <+5085>:  jg     0x480991 <PyCode_Optimize+5041>
-------------------------------------

gcc-4.6 -O1 -ftree-vectorize
-------------------------------------
0x0000000000480991 <+5041>:  mov    %eax,%ecx
0x0000000000480993 <+5043>:  sub    %edx,%ecx
0x0000000000480995 <+5045>:  mov    %ecx,(%r12,%rax,4)
0x0000000000480999 <+5049>:  movzbl 0x0(%rbp,%rax,1),%ecx
0x000000000048099e <+5054>:  lea    0x1(%rdx),%esi
0x00000000004809a1 <+5057>:  cmp    $0x9,%cl
0x00000000004809a4 <+5060>:  cmovne %edx,%esi
0x00000000004809a7 <+5063>:  cmove  %esi,%edx
0x00000000004809aa <+5066>:  setne  %cl
0x00000000004809ad <+5069>:  movzbl %cl,%ecx
0x00000000004809b0 <+5072>:  lea    0x1(%rax,%rcx,2),%rax
0x00000000004809b5 <+5077>:  cmp    %rax,%rdi
0x00000000004809b8 <+5080>:  jg     0x480991 <PyCode_Optimize+5041>
-------------------------------------

More info about the loop:
----
Py_ssize_t i;
int nops;
----

My setup:
 * Intel(R) Pentium(R) 4 CPU 3.00GHz
 * Debian Sid
 * gcc (Debian 20110106-1) 4.6.0 20110106 (experimental) [trunk revision 168538]

[...]
> 
> gcc-4.6 -O1 -ftree-vectorize
> -------------------------------------
> 0x0000000000480991 <+5041>:  mov    %eax,%ecx
> 0x0000000000480993 <+5043>:  sub    %edx,%ecx
> 0x0000000000480995 <+5045>:  mov    %ecx,(%r12,%rax,4)
> 0x0000000000480999 <+5049>:  movzbl 0x0(%rbp,%rax,1),%ecx
> 0x000000000048099e <+5054>:  lea    0x1(%rdx),%esi
> 0x00000000004809a1 <+5057>:  cmp    $0x9,%cl
> 0x00000000004809a4 <+5060>:  cmovne %edx,%esi
> 0x00000000004809a7 <+5063>:  cmove  %esi,%edx
> 0x00000000004809aa <+5066>:  setne  %cl
> 0x00000000004809ad <+5069>:  movzbl %cl,%ecx
> 0x00000000004809b0 <+5072>:  lea    0x1(%rax,%rcx,2),%rax
> 0x00000000004809b5 <+5077>:  cmp    %rax,%rdi
> 0x00000000004809b8 <+5080>:  jg     0x480991 <PyCode_Optimize+5041>
> -------------------------------------

Looks like code generation is borked.
(it lacks a compare to 0x59 or 0x5a (90), and "setne" wouldn't be the
right instruction anyway)

> Looks like code generation is borked.

I sent an email to the mailing list:
http://gcc.gnu.org/ml/gcc-help/2011-01/msg00136.html

I reported the bug to GCC:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47271

Do we have to keep this open?

> Do we have to keep this open?

Nope, let's close it.