[all-commits] [llvm/llvm-project] adb96d: [WebAssembly] Fix leak in Emscripten SjLj

[Heejin Ahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: adb96d2e76ce0c9b9e5a51a4e3dfd2c4efa4c3c3
      https://github.com/llvm/llvm-project/commit/adb96d2e76ce0c9b9e5a51a4e3dfd2c4efa4c3c3
  Author: Heejin Ahn <aheejin at gmail.com>
  Date:   2021-08-12 (Thu, 12 Aug 2021)

  Changed paths:
    M llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
    M llvm/test/CodeGen/WebAssembly/lower-em-ehsjlj.ll
    M llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll

  Log Message:
  -----------
  [WebAssembly] Fix leak in Emscripten SjLj

For SjLj, we allocate a table to record setjmp buffer info in the entry
of each setjmp-calling function by inserting a `malloc` call, and insert
a `free` call to free the buffer before each `ret` instruction.

But this is not sufficient; we have to free the buffer before we throw.
In SjLj handling, normal functions that can possibly throw or longjmp
are wrapped with an invoke and caught within the function so they don't
end up escaping the function. But three functions throw and escape the
function:
- `__resumeException` (Emscripten library function used for Emscripten
  EH)
- `emscripten_longjmp` (Emscripten library function used for Emscripten
  SjLj)
- `__cxa_throw` (libc++abi function called when for C++ `throw` keyword)

The first two functions are used to rethrow the current
exception/longjmp when the caught exception/longjmp is not for the
current function. `__cxa_throw` is used for exception, and because we
consider that a function that cannot longjmp, it escapes the function
right away, before which we should free the buffer.

Currently `lsan.test_longjmp3` and `lsan.test_exceptions_longjmp3` fail
in Emscripten; this CL fixes these.

Reviewed By: dschuff

Differential Revision: https://reviews.llvm.org/D107852