Bug 325451

Description of problem:
In RHEL 5, only the 64-bit s390 kernel is provided (not the 31-bit), but
the 31-bit compat libs are provided.  The issue is reproduced by building the
attached files with:

gcc -m31 -g -o debuggee debuggee.c demo1.s
gcc -m31 -g -o debugger debugger.c

Using ptrace() to debug a target process. On the s390 we use some 'undocumented'
calls into ptrace. These calls are, ptrace(PTRACE_PEEKUSR_AREA...) and
ptrace(PTRACE_POKEUSR_AREA...).  The calls should read/write a structure filled
with register values that represent a snapshot of the target process. This was
working fine on RHEL 4, but on RHEL5 31bit, it fails with an EIO failure.  I've
attached a small demo of the problem. './debugger' will run the demo. If you
convert the demo for 64bit instead of 31bit then it works as expected.

I expect to see :
process stopped
read PC = 0x004004bc
wrote PC = 0x004004c0
We're back!

But on RHEL5 I get :
process stopped
PTRACE_PEEKUSR_AREA, failed
 : Input/output error
read PC = (nil)
PTRACE_PEEKUSR_AREA, failed
 : Input/output error
wrote PC = 0x00000004
We're back!

I thought the way that the ptrace(PTRACE_PEEKUSR_AREA...) call worked
was, you pass an offset of the first register to read, and a size
indicating the amount of registers to read, (such that the size value
could be any multiple of the register size), and your buffer would be
filled with register values from the indicated offset up to the size
allowed in pt_area->len. If that was the case then you could read one
register by passing an offset and a size of one register. Is this idea
correct?

------------

On RHEL 4, glibc-kernheaders provides 31-bit and 64-bit versions of ptrace.h:

# rpm -ql glibc-kernheaders | grep ptrace.h

/usr/include/asm-s390/ptrace.h
/usr/include/asm-s390x/ptrace.h
/usr/include/asm/ptrace.h
/usr/include/linux/ptrace.h

# cat /usr/include/asm/ptrace.h 

#ifndef __ASM_STUB_PTRACE_H__
# define __ASM_STUB_PTRACE_H__
# if defined __s390__ && !defined __s390x__
#  include <asm-s390/ptrace.h>
# endif
# if defined __s390x__
#  include <asm-s390x/ptrace.h>
# endif
#endif

but on RHEL 5, there's only one version:

# rpm -ql kernel-headers | grep ptrace.h

/usr/include/asm/ptrace.h
/usr/include/linux/ptrace.h

Would providing the 31-bit version of ptrace.h fix this, or is the error
related to using ptrace(PTRACE_PEEKUSR_AREA...)?

Version-Release number of selected component (if applicable):
kernel-2.6.18-52.el5

How reproducible:
100%

Steps to Reproduce:
1. gcc -m31 -g -o debuggee debuggee.c demo1.s
2. gcc -m31 -g -o debugger debugger.c
3. ./debugger