[libcxx-commits] [PATCH] D106626: [libunwind] Allow restoring SP while unwinding.

[Marco Vanotti via Phabricator via libcxx-commits]

charco updated this revision to Diff 361064.
charco edited the summary of this revision.
charco added a comment.

update commit msg


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D106626/new/

https://reviews.llvm.org/D106626

Files:
  libunwind/src/DwarfInstructions.hpp


Index: libunwind/src/DwarfInstructions.hpp
===================================================================
--- libunwind/src/DwarfInstructions.hpp
+++ libunwind/src/DwarfInstructions.hpp
@@ -167,6 +167,16 @@
 
        // restore registers that DWARF says were saved
       R newRegisters = registers;
+
+      // Typically, the CFA is the stack pointer at the call site in
+      // the previous frame. However, there are scenarios in which this is not
+      // true. For example, if we switched to a new stack. In that case, the
+      // value of the previous SP might be indicated by a CFI directive.
+      //
+      // We set the SP here to the CFA, allowing for it to be overridden
+      // by a CFI directive later on.
+      newRegisters.setSP(cfa);
+
       pint_t returnAddress = 0;
       const int lastReg = R::lastDwarfRegNum();
       assert(static_cast<int>(CFI_Parser<A>::kMaxRegisterNumber) >= lastReg &&
@@ -200,10 +210,6 @@
         }
       }
 
-      // By definition, the CFA is the stack pointer at the call site, so
-      // restoring SP means setting it to CFA.
-      newRegisters.setSP(cfa);
-
       isSignalFrame = cieInfo.isSignalFrame;
 
 #if defined(_LIBUNWIND_TARGET_AARCH64)


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