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Add a comment documenting the reason for subtracting one from the IP value

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after each pass of the loop.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@5012
This commit is contained in:
Tom Hughes 2005-11-05 00:17:21 +00:00
parent 100bb1fdf9
commit efaaa0b74a
1 changed files with 15 additions and 0 deletions
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15
coregrind/m_stacktrace.c
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@ -110,6 +110,21 @@ UInt VG_(get_StackTrace2) ( Addr* ips, UInt n_ips,
ips[0] = ip;
i = 1;
/* Loop unwinding the stack. Note that the IP value we get on
* each pass (whether from CFI info or a stack frame) is a
* return address so is actually after the calling instruction
* in the calling function.
*
* Because of this we subtract one from the IP after each pass
* of the loop so that we find the right CFI block on the next
* pass - otherwise we can find the wrong CFI info if it happens
* to change after the calling instruction and that will mean
* that we will fail to unwind the next step.
*
* This most frequently happens at the end of a function when
* a tail call occurs and we wind up using the CFI info for the
* next function which is completely wrong.
*/
while (True) {
if (i >= n_ips)