[slime-devel] Debugging SBCL...
I am trying to debug a web app (based on hunchentoot and weblocks). Let's say I have a function (defun test-func(a) (let ((b 1) (c 2)) (break))) I call this (test-func 0) from (defun weblocks-dispatcher (request) ....) When I hit break, am I supposed to see a, b and c as local variables in the frame? All I can see is the request parameter of weblocks-dispatcher and not even the frame for test-func, what I am missing? Backtrace: 0: (BREAK "break") Locals: SB-KERNEL::ARGUMENTS = NIL SB-KERNEL::DATUM = "break" 1: (WEBLOCKS::WEBLOCKS-DISPATCHER #<HUNCHENTOOT:REQUEST {CFAAB71}>) Locals: SB-DEBUG::ARG-0 = #<HUNCHENTOOT:REQUEST {CFAAB71}> I am using the very latest SBCL 1.0.36 and latest cvs slime. Thank you, Andrei
On 25 March 2010 23:18, Andrei Stebakov <lispercat@gmail.com> wrote:
I am trying to debug a web app (based on hunchentoot and weblocks). Let's say I have a function
(defun test-func(a) (let ((b 1) (c 2)) (break)))
I call this (test-func 0) from (defun weblocks-dispatcher (request) ....) When I hit break, am I supposed to see a, b and c as local variables in the frame? All I can see is the request parameter of weblocks-dispatcher and not even the frame for test-func, what I am missing?
It all comes down to: "Use a higher debug level." Either use DEBUG 2 -- or 3, if you really want the maximum info, but 3 has both notable runtime and compile-time costs in SBCL. In addition to having a low debug-level, you're not seeing the frame in your example because BREAK has been tail-called. Changing the code to (defun test-func(a) (let ((b 1) (c 2)) (break) t)) gets rid of the tail call, so you see the frame: 0: (BREAK "break") 1: (TEST-FUNC #<unavailable argument>) Locals: SB-DEBUG::ARG-0 = :<NOT-AVAILABLE> 2: (SB-INT:SIMPLE-EVAL-IN-LEXENV (TEST-FUNC 1) #<NULL-LEXENV>) Also, since the values are never used the variables are optimized away. Changing the code to (defun test-func (a) (let ((b (+ a 1)) (c (+ a 2))) (break) (+ a b c))) gets you 1: (TEST-FUNC 1) Locals: SB-DEBUG::ARG-0 = 1 2: (SB-INT:SIMPLE-EVAL-IN-LEXENV (TEST-FUNC 1) #<NULL-LEXENV>) -- you're still missing the name of the argument, and B and C have been optimized away as they are used only once. The code has been compiled as if you had written (+ a (+ a 1) (+ a 2)) instead of (+ a b c). Debug 2 is enough to sort that out: (defun test-func (a) (declare (optimize (debug 2))) (let ((b (+ a 1)) (c (+ a 2))) (break) (+ a b c))) 0: (BREAK "break") 1: (TEST-FUNC 1) Locals: A = 1 B = 2 C = 3 2: (SB-INT:SIMPLE-EVAL-IN-LEXENV (TEST-FUNC 1) #<NULL-LEXENV>) ...but you see, already the higher debug level is starting to cost in the form of elided optimizations -- but for many applications DEBUG 2 is a nice halfway house. Cheers, -- Nikodemus
Andrei Stebakov <lispercat@gmail.com> writes:
I am trying to debug a web app (based on hunchentoot and weblocks). Let's say I have a function
(defun test-func(a) (let ((b 1) (c 2)) (break)))
I call this (test-func 0) from (defun weblocks-dispatcher (request) ....) When I hit break, am I supposed to see a, b and c as local variables in the frame? All I can see is the request parameter of weblocks-dispatcher and not even the frame for test-func, what I am missing?
Backtrace: 0: (BREAK "break") Locals: SB-KERNEL::ARGUMENTS = NIL SB-KERNEL::DATUM = "break" 1: (WEBLOCKS::WEBLOCKS-DISPATCHER #<HUNCHENTOOT:REQUEST {CFAAB71}>) Locals: SB-DEBUG::ARG-0 = #<HUNCHENTOOT:REQUEST {CFAAB71}>
I am using the very latest SBCL 1.0.36 and latest cvs slime.
Thank you, Andrei
Maybe the call to TEST-FUNC is a tail call and hence optimized away by SBCL? Try recompiling WEBLOCKS-DISPATCHER with a higher debug settings. Tip: You can use C-u C-c C-c in Slime with SBCL to compile the toplevel function at point with highest debug settings. -T.
"Tobias C. Rittweiler" <tcr@freebits.de> writes:
Andrei Stebakov <lispercat@gmail.com> writes:
I am trying to debug a web app (based on hunchentoot and weblocks). Let's say I have a function
(defun test-func(a) (let ((b 1) (c 2)) (break)))
I call this (test-func 0) from (defun weblocks-dispatcher (request) ....) When I hit break, am I supposed to see a, b and c as local variables in the frame? All I can see is the request parameter of weblocks-dispatcher and not even the frame for test-func, what I am missing?
Backtrace: 0: (BREAK "break") Locals: SB-KERNEL::ARGUMENTS = NIL SB-KERNEL::DATUM = "break" 1: (WEBLOCKS::WEBLOCKS-DISPATCHER #<HUNCHENTOOT:REQUEST {CFAAB71}>) Locals: SB-DEBUG::ARG-0 = #<HUNCHENTOOT:REQUEST {CFAAB71}>
I am using the very latest SBCL 1.0.36 and latest cvs slime.
Thank you, Andrei
Maybe the call to TEST-FUNC is a tail call and hence optimized away by SBCL? Try recompiling WEBLOCKS-DISPATCHER with a higher debug settings.
Silly me answering mails in the morning before really being waked up; the call to BREAK in your TEST-FUNC is a tail call, and hence the stack frames of TEST-FUNC is reused for BREAK. Try recompiling TEST-FUNC with higher debug settings, or move the call to break out of tail call position. -T.
participants (3)
-
Andrei Stebakov -
Nikodemus Siivola -
Tobias C. Rittweiler