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Issue #6042:

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lnotab-based tracing is very complicated and isn't documented very well.  There
were at least 3 comment blocks purporting to document co_lnotab, and none did a
very good job. This patch unifies them into Objects/lnotab_notes.txt which
tries to completely capture the current state of affairs.

I also discovered that we've attached 2 layers of patches to the basic tracing
scheme. The first layer avoids jumping to instructions that don't start a line,
to avoid problems in if statements and while loops.  The second layer
discovered that jumps backward do need to trace at instructions that don't
start a line, so it added extra lnotab entries for 'while' and 'for' loops, and
added a special case for backward jumps within the same line. I replaced these
patches by just treating forward and backward jumps differently.
This commit is contained in:
Jeffrey Yasskin 2009-05-23 23:23:01 +00:00
parent 3724d6c392
commit 655d835415
6 changed files with 157 additions and 209 deletions
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25
Python/ceval.c
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@ -3591,33 +3591,30 @@ _PyEval_CallTracing(PyObject *func, PyObject *args)
return result;
}
/* See Objects/lnotab_notes.txt for a description of how tracing works. */
static int
maybe_call_line_trace(Py_tracefunc func, PyObject *obj,
PyFrameObject *frame, int *instr_lb, int *instr_ub,
int *instr_prev)
{
int result = 0;
int line = frame->f_lineno;
/* If the last instruction executed isn't in the current
instruction window, reset the window. If the last
instruction happens to fall at the start of a line or if it
represents a jump backwards, call the trace function.
instruction window, reset the window.
*/
if ((frame->f_lasti < *instr_lb || frame->f_lasti >= *instr_ub)) {
int line;
if (frame->f_lasti < *instr_lb || frame->f_lasti >= *instr_ub) {
PyAddrPair bounds;
line = PyCode_CheckLineNumber(frame->f_code, frame->f_lasti,
&bounds);
if (line >= 0) {
frame->f_lineno = line;
result = call_trace(func, obj, frame,
PyTrace_LINE, Py_None);
}
line = _PyCode_CheckLineNumber(frame->f_code, frame->f_lasti,
&bounds);
*instr_lb = bounds.ap_lower;
*instr_ub = bounds.ap_upper;
}
else if (frame->f_lasti <= *instr_prev) {
/* If the last instruction falls at the start of a line or if
it represents a jump backwards, update the frame's line
number and call the trace function. */
if (frame->f_lasti == *instr_lb || frame->f_lasti < *instr_prev) {
frame->f_lineno = line;
result = call_trace(func, obj, frame, PyTrace_LINE, Py_None);
}
*instr_prev = frame->f_lasti;