On 04/28, Denys Vlasenko wrote:
>
> On 04/28/2014 07:34 PM, Oleg Nesterov wrote:
> >
> > It seems that you are right. But it would be really great if you also
> > provide the test-case which proves the fix ;)
>
> Working on a testcase for this. So far covered div (test1)
> and cmpxchg (test2).
>
> Reproduced failure on a fairly old 3.10.11 kernel:
Just in case, confirm. Reproduced on v3.14 + all recent uprobes changes.
Thanks.
> # gcc -Os -Wall test_riprel.c -o test_riprel
> # ./test_riprel
> test1: pass
> test2: pass
> # perf probe -x ./test_riprel probe1
> # perf record -e probe_test:probe1 ./test_riprel
> test1: FAIL
> test2: pass
> # perf probe -x ./test_riprel probe2
> # perf record -e probe_test:probe2 ./test_riprel
> test1: pass
> test2: FAIL
>
> Source:
>
> test_riprel.c
> ==================
> #include <stdio.h>
>
> static const char *const fail_pass[] = { "FAIL", "pass" };
>
> long two = 2;
> long test1()
> {
> long ax=0, dx=0;
> asm volatile("\n"
> " xor %%edx,%%edx\n"
> " lea 2(%%edx),%%eax\n"
> // We divide 2 by 2. Result (in eax) should be 1:
> " probe1: .globl probe1\n"
> " divl two(%%rip)\n"
> // If we have a bug (eax mangled on entry) the result will be 2,
> // because eax gets restored by probe machinery.
> : "=a" (ax), "=d" (dx) /*out*/
> : "0" (ax), "1" (dx) /*in*/
> : "memory" /*clobber*/
> );
> dprintf(2, "%s: %s\n", __func__, fail_pass[ax == 1]);
> return ax;
> }
>
> long val2 = 0;
> long test2()
> {
> long old_val2 = val2;
> long ax=0, dx=0;
> asm volatile("\n"
> " mov val2,%%eax\n" // eax := val2
> " lea 1(%%eax),%%edx\n" // edx := eax+1
> // eax is equal to val2. cmpxchg should store edx to val2:
> " probe2: .globl probe2\n"
> " cmpxchg %%edx,val2(%%rip)\n"
> // If we have a bug (eax mangled on entry), val2 will stay unchanged
> : "=a" (ax), "=d" (dx) /*out*/
> : "0" (ax), "1" (dx) /*in*/
> : "memory" /*clobber*/
> );
> dprintf(2, "%s: %s\n", __func__, fail_pass[val2 == old_val2 + 1]);
> return ax == dx;
> }
>
> int main()
> {
> test1();
> test2();
> return 0;
> }
>
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