Hi Song,
On 08/21/2018 10:53 AM, Ravi Bangoria wrote:
> Hi Song,
>
>> However, if I start a.out AFTER enabling the uprobe, there is something wrong:
>>
>> root@virt-test:~# ~/a.out
>> 11
>> semaphore 0 <<< this should be non-zero, as the uprobe is already enabled
In this testcase, semaphore variable is stored into .bss:
$ nm test | grep semaphore
0000000010010c5e B semaphore
$ readelf -SW ./test | grep "data\|bss"
[22] .data PROGBITS 0000000010010c58 000c58 000004 00 WA 0 0 1
[23] .bss NOBITS 0000000010010c5c 000c5c 000004 00 WA 0 0 2
I'm not so sure but I guess .bss data initialization happens after
calling uprobe_mmap() and thus you are seeing semaphore as 0.
To verify this, if I force to save semaphore into data section by
assigning non-zero value to it:
volatile short semaphore = 1
$ nm test | grep semaphore
0000000010010c5c D semaphore
$ readelf -SW ./test | grep "data\|bss"
[22] .data PROGBITS 0000000010010c58 000c58 000006 00 WA 0 0 2
[23] .bss NOBITS 0000000010010c5e 000c5e 000002 00 WA 0 0 1
increment/decrement works fine.
Ravi
