Add support for debug information for a native debugger #9334
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CT Test Results 7 files 638 suites 3h 14m 51s ⏱️ For more details on these failures, see this check. Results for commit fcbaf38. ♻️ This comment has been updated with latest results. To speed up review, make sure that you have read Contributing to Erlang/OTP and that all checks pass. See the TESTING and DEVELOPMENT HowTo guides for details about how to run test locally. Artifacts// Erlang/OTP Github Action Bot |
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Temporary variables generated by compiler passes must have names that are not allowed in Erlang source code to ensure that they will not be included in debug information.
Add `split_blocks_after/4` to split the block after the instruction for which the predicate returns `true`. Rename `split_blocks/4` to `split_blocks_before/4`.
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The `beam_debug_info` compiler option will insert `debug_line`
instructions on lines containing executable code, and it will maintain
information about which variables the BEAM registers contain at each
`debug_line` instruction. This information will be inserted into a
"DbgB" chunk in the BEAM file.
When a `debug_line` is executed, the current stack frame (if any) is
guaranteed to be fully initialized. The number of live X registers is
given as the second operand for the `debug_line` instruction (it is
guaranteed that there are no "holes").
Here is an example where the debug information translated to text has
been inserted as comments before the lines they apply to:
%% function entry (no stack frame); x0, x1, x2 are live
sum(A, B, _Ignored) ->
%% no stack frame; A in x0, B in x1, _Ignored in x2
C = A + B,
%% no stack frame; B in x1, C in x0
io:format("~p\n", [C]),
%% stack frame size is 1; C in y0
D = 10 * C,
%% stack frame size is 1; C in y0, D in x0
{ok,D}.
Note that not all variables are available in the debug information.
For example, before the call to `io:format/2`, the sum of A and B have
overwritten the register that used to hold the value of A, and the value
for _Ignore was wiped out by the `+` operation.
The size of the current stack frame is also given at each `debug_line`
to be able to easily find the beginning of the previous stack frame.
This commit implements support for loading the debug information from
a BEAM file and the `code:get_debug_info/1` BIF for retrieving the
debug information.
As an example, given the following module:
-module(example). % 1
-export([foo/1]). % 2
foo(A) -> % 4
case A of % 5
0 -> % 6
B = 1, % 7
io:format("~p\n", [B]); % 8
1 -> % 9
C = [1,2,3], % 10
io:format("~p\n", [C]) % 11
end, % 12
A. % 13
sign(N) when N < 0 -> 1; % 15
sign(N) when N == 0 -> 0; % 16
sign(_) -> 1. % 17
here is how to compile it with BEAM debug information and
display the debug information:
1> c(example, beam_debug_info).
{ok,example}
2> code:get_debug_info(example).
[{4,{entry,[{1,{x,0}}]}},
{5,{1,[{<<"A">>,{y,0}}]}},
{7,{1,[{<<"A">>,{y,0}}]}},
{8,{1,[{<<"B">>,{value,1}},{<<"A">>,{y,0}}]}},
{10,{1,[{<<"A">>,{y,0}}]}},
{11,{1,[{<<"C">>,{value,[1,2,3]}},{<<"A">>,{y,0}}]}},
{13,{1,[{<<"A">>,{y,0}}]}},
{15,{entry,[{1,{x,0}}]}},
{15,{none,[{<<"N">>,{x,0}}]}},
{16,{none,[{<<"N">>,{x,0}}]}},
{17,{none,[]}}]
List elements having the frame size `entry` refers to a `debug_line`
instruction at the beginning of the function (before all
clauses). Note that the line number for such entries *may* be the same
as the line number for the first clause. All other line numbers are
guaranteed to be unique.
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This pull request introduces support for adding debug information to BEAM files for a native debugger and for the BEAM loader to load that information. For more information, see the individual commit messages.
This is one of the components needed for the new debugger being developed by WhatsApp.