[libcxx-commits] [PATCH] D115020: [libunwind] Fix unwind_leaffunction.pass.cpp

[Leonard Chan via Phabricator via libcxx-commits]

leonardchan created this revision.
leonardchan added reviewers: danielkiss, vvereschaka.
leonardchan added a project: libunwind.
Herald added subscribers: libcxx-commits, pengfei, kristof.beyls.
Herald added a reviewer: libunwind.
leonardchan requested review of this revision.
Herald added a project: LLVM.

It's possible for this test not to pass if the libc used does not provide unwind info for `raise`. We can replace it with `__builtin_cast`, which can lead to a SIGTRAP on x86_64 and a SIGILL on aarch64.

Using this alternative, a `nop` is needed before the `__builtin_cast`. This is because libunwind incorrectly decrements `pc`, which can cause `pc` to jump into the previous function and use the incorrect FDE.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D115020

Files:
  libunwind/test/unwind_leaffunction.pass.cpp


Index: libunwind/test/unwind_leaffunction.pass.cpp
===================================================================
--- libunwind/test/unwind_leaffunction.pass.cpp
+++ libunwind/test/unwind_leaffunction.pass.cpp
@@ -39,11 +39,17 @@
 }
 
 __attribute__((noinline)) void crashing_leaf_func(void) {
-  raise(SIGSEGV);
+  // libunwind searches for the address before the return address which points
+  // to the trap instruction. NOP guarantees the trap instruction is not the
+  // first instruction of the function.
+  // We should keep this here for other unwinders that also decrement pc.
+  __asm__ __volatile__("nop");
+  __builtin_trap();
 }
 
 int main(int, char**) {
-  signal(SIGSEGV, signal_handler);
+  signal(SIGTRAP, signal_handler);
+  signal(SIGILL, signal_handler);
   crashing_leaf_func();
   return -2;
 }


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