[Lldb-commits] [PATCH] D50478: WIP: Basic tail call frame support

[Vedant Kumar via Phabricator via lldb-commits]

vsk created this revision.
Herald added a subscriber: JDevlieghere.

This is a prototype of tail call frame support for lldb based on
compiler support from https://reviews.llvm.org/D49887. It isn't ready for review. I'm sharing the
proof-of-concept to give a heads-up about this coming down the pipeline,
and/or to answer any early questions.

Demo (see the included tail5.cc test case):

+ /Users/vsk/src/builds/llvm-project-tailcall-RA/bin//clang++ tail5.cc -o tail5.cc.out -g -mllvm -callsite-debuginfo-experimental=true -O2
+ xcrun lldb -o 'b sink' -o r -o bt -o quit tail5.cc.out
(lldb) target create "tail5.cc.out"
Current executable set to 'tail5.cc.out' (x86_64).
(lldb) b sink
Breakpoint 1: where = tail5.cc.out`sink() + 4 at tail5.cc:2, address = 0x0000000100000f64
(lldb) r
tail5.cc.out was compiled with optimization - stepping may behave oddly; variables may not be available.
Process 21540 stopped

- thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1 frame #0: 0x0000000100000f64 tail5.cc.out`sink() at tail5.cc:2 [opt] 1    volatile int x;

-> 2    void __attribute__((noinline)) sink() { x++; }

  3    void __attribute__((noinline)) D() { sink(); /* tail */ }
  4    void __attribute__((disable_tail_calls, noinline)) C() { D(); /* regular */ }
  5    void __attribute__((noinline)) B() { C(); /* tail */ }
  6    int __attribute__((disable_tail_calls)) main() { B(); /* regular */ }

Target 0: (tail5.cc.out) stopped.

Process 21540 launched: '/Users/vsk/src/llvm-project-tailcall/lldb/test/testcases/functionalities/tail_call_frames/tail5.cc.out' (x86_64)
(lldb) bt

- thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
  - frame #0: 0x0000000100000f64 tail5.cc.out`sink() at tail5.cc:2 [opt] frame #1: 0x0000000100000f89 tail5.cc.out`C() at tail5.cc:4 [opt] frame #2: 0x0000000100000fa9 tail5.cc.out`main at tail5.cc:6 [opt] frame #3: 0x00007fff57147015 libdyld.dylib`start + 1 frame #4: 0x00007fff57147015 libdyld.dylib`start + 1

(lldb) quit
+ /Users/vsk/src/builds/llvm-project-tailcall-RA/bin//lldb -o 'b sink' -o r -o 'log enable -f tail5.cc.log lldb step' -o bt -o quit tail5.cc.out
(lldb) target create "tail5.cc.out"
Current executable set to 'tail5.cc.out' (x86_64).
(lldb) b sink
Breakpoint 1: where = tail5.cc.out`sink() + 4 at tail5.cc:2, address = 0x0000000100000f64
(lldb) r
tail5.cc.out was compiled with optimization - stepping may behave oddly; variables may not be available.
Process 21544 stopped

- thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1 frame #0: 0x0000000100000f64 tail5.cc.out`sink() at tail5.cc:2 [opt] 1    volatile int x;

-> 2    void __attribute__((noinline)) sink() { x++; }

  3    void __attribute__((noinline)) D() { sink(); /* tail */ }
  4    void __attribute__((disable_tail_calls, noinline)) C() { D(); /* regular */ }
  5    void __attribute__((noinline)) B() { C(); /* tail */ }
  6    int __attribute__((disable_tail_calls)) main() { B(); /* regular */ }

Process 21544 launched: '/Users/vsk/src/llvm-project-tailcall/lldb/test/testcases/functionalities/tail_call_frames/tail5.cc.out' (x86_64)
(lldb) log enable -f tail5.cc.log lldb step
(lldb) bt

- thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
  - frame #0: 0x0000000100000f64 tail5.cc.out`sink() at tail5.cc:2 [opt] frame #1: 0x0000000000000010 tail5.cc.out`D() - 4294971232 [opt] frame #2: 0x0000000100000f89 tail5.cc.out`C() at tail5.cc:4 [opt] frame #3: 0x0000000000000030 tail5.cc.out`B() - 4294971232 [opt] frame #4: 0x0000000100000fa9 tail5.cc.out`main at tail5.cc:6 [opt] frame #5: 0x00007fff57147015 libdyld.dylib`start + 1 frame #6: 0x00007fff57147015 libdyld.dylib`start + 1


https://reviews.llvm.org/D50478

Files:
  lldb/include/lldb/Symbol/Block.h
  lldb/include/lldb/Symbol/Function.h
  lldb/include/lldb/Symbol/SymbolFile.h
  lldb/include/lldb/Target/StackFrame.h
  lldb/include/lldb/Target/StackFrameList.h
  lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/tail.cc
  lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/tail2.cc
  lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/tail3.cc
  lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/tail4.cc
  lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/tail5.cc
  lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/test.sh
  lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
  lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h
  lldb/source/Symbol/Block.cpp
  lldb/source/Symbol/Function.cpp
  lldb/source/Target/StackFrameList.cpp

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