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

Guangwen Feng
2016-08-16T03:08:52Z

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
>
>
> .
>