Messages in this thread |  | | From | Ravi Bangoria <> | Subject | Re: [PATCH v9 0/4] Uprobes: Support SDT markers having reference count (semaphore) | Date | Tue, 21 Aug 2018 11:50:43 +0530 |
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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
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