Bug 188774

Description of problem:
The ftruncate system call writes register %ebx instead of preserving %ebx.

Version-Release number of selected component (if applicable):
kernel-2.6.16-1.2080_FC5

How reproducible:
Always

Steps to Reproduce:
1. Create a throw-away read-write file named foo_file using "date >foo_file".
2. Compile this program with "gcc -o ebx -nostartfiles -nostdlib ebx.S"
The 'int3' are for ease of use with gdb.
-----input file ebx.S
#include <asm/unistd.h>

#define O_RDWR               02

_start: .globl _start
        nop
        int3
        movl $ O_RDWR,%ecx
        movl $ foo,%ebx
        movl $__NR_open,%eax
        int $0x80
        subl %ecx,%ecx  # 0
        movl %eax,%ebx  # fd
        movl $__NR_ftruncate,%eax
        int $0x80  # should not change %ebx, but does in 2.6.16-1.2080_FC5
        nop
        int3
        movl $__NR_exit,%eax
        int $0x80  # exit code is %ebx: should be fd returned by __NR_open

        .data
foo:
        .asciz "foo_file"
-----
The program truncates 'foo_file' to have length 0, then exits with return code
equal what was left in %ebx by ftruncate, which should be the fd (the first
parameter to ftruncate.)
3. Run executable file ebx under gdb.  Step through, and note that the ftruncate
syscall chagnes %ebx.
  
Actual results:
The ftruncate syscall changes %ebx.  The values I see under gdb are %ebx=6 before
the call, and %ebx=1 after the call.  When run under strace, the __NR_open
returns 3, the __NR_ftruncate changes %ebx from 3 to 1, and the __NR_exit
process return value is 1 instead of 3:
-----
$ strace ./ebx
execve("./ebx", ["./ebx"], [/* 34 vars */]) = 0
open("foo_file", O_RDWR)                = 3
ftruncate(3, 0)                         = 0
_exit(1)                                = ?  ## should be _exit(3) instead
Process 13430 detached
-----

Expected results:
ftrunctate, like all syscalls, should preserve %ebx, %esi, %edi, %ebp, %esp.
(Registers %eax, %ecx, %edx, and %eflags may change.)
[This is the same convention as C subroutine calls.]

Additional info:
%ebx is preserved in RHEL4 (nahant) kernel-2.6.9-22.0.1.EL,
and in Fedora Core 4 kernel-2.6.14-1.1637_FC4.