[LTP] [PATCH] syscalls/signal06: fix test for regression with earlier version of gcc and kernel

[Guangwen Feng]

Hi!

Thanks for your review and confirmation!

Regards,
Guangwen Feng

On 08/08/2016 04:44 PM, Li Wang wrote:
> On 5 August 2016 at 14:58, Guangwen Feng <fenggw-fnst@cn.fujitsu.com> wrote:
>> 1. Currently, following code is incorrect on some releases with
>>    earlier version of gcc(tested on RHEL5.11GA):
>>
>>         while (D == d && loop < LOOPS) {
>>
>>    Because the argument in function test(double d) is used via (%rsp),
>>    but here we actually need a xmm register to trigger the fpu bug.
>>    So use global value instead to make sure to take use of xmm.
> 
> Sounds reasonable! To verify that I did disassemble work of the
> pre/post signal06 for comparison:
> 
> signal06 old version
> -------------------------
> void test(double d)
> {
>         int loop = 0;
>         int pid = getpid();
>   402846:       89 c7                   mov    %eax,%edi
> 
>         D = d;
>   402848:       f2 0f 11 05 b0 27 21    movsd  %xmm0,0x2127b0(%rip)
>     # 615000 <D>
>   40284f:       00
>         while (D == d && loop < LOOPS) {
>   402850:       f2 0f 10 05 a8 27 21    movsd  0x2127a8(%rip),%xmm0
>     # 615000 <D>
>   402857:       00
>   402858:       66 0f 2e 44 24 08       ucomisd 0x8(%rsp),%xmm0
>   40285e:       0f 85 b8 00 00 00       jne    40291c <test+0xec>
>   402864:       0f 8a b2 00 00 00       jp     40291c <test+0xec>
>   40286a:       31 db                   xor    %ebx,%ebx
>   40286c:       ba c8 00 00 00          mov    $0xc8,%edx
>   402871:       be 01 00 00 00          mov    $0x1,%esi
>   402876:       eb 0a                   jmp    402882 <test+0x52>
>   402878:       81 fb 10 27 00 00       cmp    $0x2710,%ebx
>   40287e:       66 90                   xchg   %ax,%ax
>   402880:       74 6d                   je     4028ef <test+0xbf>
> 
> 
> after applying this patch
> ------------------------------
> void test(void)
> {
>         int loop = 0;
>   402c58:       bb 00 00 00 00          mov    $0x0,%ebx
>         int pid = getpid();
> 
>         D = VALUE;
>         while (D == VALUE && loop < LOOPS) {
>   402c5d:       0f 85 b5 00 00 00       jne    402d18 <test+0xe8>
>   402c63:       89 c7                   mov    %eax,%edi
>                 /* sys_tkill(pid, SIGHUP); asm to avoid save/reload
>                  * fp regs around c call */
>                 asm ("" : : "a"(__NR_tkill), "D"(pid), "S"(SIGHUP));
>   402c65:       ba c8 00 00 00          mov    $0xc8,%edx
>   402c6a:       be 01 00 00 00          mov    $0x1,%esi
> {
>         int loop = 0;
>         int pid = getpid();
> 
>         D = VALUE;
>         while (D == VALUE && loop < LOOPS) {
>   402c6f:       66 0f 28 d1             movapd %xmm1,%xmm2
>   402c73:       eb 11                   jmp    402c86 <test+0x56>
>   402c75:       0f 1f 00                nopl   (%rax)
>   402c78:       66 0f 2e c2             ucomisd %xmm2,%xmm0
>   402c7c:       75 1d                   jne    402c9b <test+0x6b>
>   402c7e:       81 fb a0 86 01 00       cmp    $0x186a0,%ebx
>   402c84:       74 65                   je     402ceb <test+0xbb>
> 
> 
>>
>> 2. Although this regression test is designed to trigger SIGSEGV
>>    intentionally, on some releases with old kernel(tested on RHEL5.11GA),
>>    this will still lead to segmentation fault that terminate the program
>>    and break the test even though compiling with -O2.  So slightly adjust
>>    the weight of the codes in child thread to depress SIGSEGV trigger's
>>    chance while increase LOOPS to ensure reproducible.
> 
> This is also acceptable, seems too many signals more than one kenel
> can handled that easily cause segmental fault at the moment.
> 
> I test this patch on RHEL5.11(reproduced) and RHEL7.2(pass), it works fine.
> 
> Regards,
> Li Wang
> 
> 
> .
>