Hi,
On Tue, Sep 8, 2020 at 6:23 PM Ulrich Windl <Ulrich.Windl@xxxxxxxxxxxxxxxxxxxx> wrote:
Hi!
vbuf is initialized: It has some address on the stack, so "if (value != vbuf)" is comparing adresses, if I got it right...
vbuf having some address on stack and "if(value!=vbuf)" is comparing addresses doesn't necessarily implies that vbuf is initialized.
I am still not clear about where vbuf is initialized.
Also, expecting some information regarding my queries in below mail.
Thanks,
Amit
>>> Amit anand <amit.table@xxxxxxxxx> schrieb am 08.09.2020 um 13:56 in Nachricht
<CAMkFpM5NFmN+pc_cztmMZW=j1vn2RYC16AgJ3LYL6RSgdqP1eA@xxxxxxxxxxxxxx>:
> Hi systemd-devel team,
>
> I am trying to understand where "vbuf" is initialized in function
> "token_match_attr()" in file udev-rules.c
>
> Below code snippet :
> static bool* token_match_attr*(UdevRuleToken *token, sd_device *dev,
> UdevEvent *event) {
> *char* nbuf[UTIL_NAME_SIZE], *vbuf*[UTIL_NAME_SIZE]; // Here, vbuf is
> defined, however not initialized.
> *const char* *name, **value; *// Here, value is declared to be of
> type const char *, however, not initialized.
> ...
> ... // some code
> ...
> switch (token->attr_subst_type) { // *Event 1* : This evaluates to
> SUBST_TYPE_PLAIN
> ...
> case *SUBST_TYPE_PLAIN*: if (sd_device_get_sysattr_value(dev, name,
> &value) < 0) // *Event 2* :The if condition evaluates to false.
> return false;
> break;
> ...// some code
> ...
> }
>
> if (token->attr_match_remove_trailing_whitespace) { // *Event
> 4*: If condition evaluates to true
> if (value != vbuf) { // *Event 5* : vbuf and value
> are both declared but not initialized. Comparison is done without
> initializing "vbuf" and "value".
> strscpy(vbuf, sizeof(vbuf), value);
> value = vbuf;
> } // End of if.
>
> delete_trailing_chars(vbuf, NULL); // *Event 6*:
> trying to delete trailing chars from "vbuf" which is not initialzed. ??
> } // End of outer if.
> ... // some code
> } /End of function : *token_match_attr()*
>
> Below are my queries :
> 1. *Event 5 *above, we are comparing two resources ("value" and "vbuf")
> even before initializing them.
> Are we doing this comparision to do decision making based on whether
> the pointer type variable "value" is pointing to "vbuf" or not.
> *Query*: Kindly confirm whether my understanding is correct.
>
> 2. *Event 6* above, delete_trailing_chars(vbuf, NULL) is called outside *if
> (value != vbuf).*
> This implies there may occur a situation where:
> step 1 ) *if (value != vbuf) *condition fails --> step 2 )
> *vbuf* is not initialzed inside the *if(value != vbuf) *--> step 3 )
> delete_trailing_chars(*vbuf*, NULL).
> Here, delete_trailing_chars() called for "*vbuf*" which is not necessarily
> initiazlied.
> *Query*: Kindly let me know if my understanding is correct or I am missing
> something.
>
> Thanks,
> Amit
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