X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=docs%2FExceptionHandling.html;h=d597ffb3c8b31703603ba85a1fed892f82ef147d;hb=a75ce9f5d2236d93c117e861e60e6f3f748c9555;hp=f67954f7e2b17b5bb5777cfb04b760c2ed44f259;hpb=29626642271ae810dd526de8afa151484452abe0;p=oota-llvm.git diff --git a/docs/ExceptionHandling.html b/docs/ExceptionHandling.html index f67954f7e2b..d597ffb3c8b 100644 --- a/docs/ExceptionHandling.html +++ b/docs/ExceptionHandling.html @@ -4,7 +4,7 @@ Exception Handling in LLVM - @@ -20,6 +20,7 @@
  • Introduction
    1. Itanium ABI Zero-cost Exception Handling
      2. +
    2. Setjmp/Longjmp Exception Handling
    3. Overview
  • LLVM Code Generation @@ -38,6 +39,8 @@
  • llvm.eh.sjlj.setjmp
  • llvm.eh.sjlj.longjmp
  • llvm.eh.sjlj.lsda
    • +
  • llvm.eh.sjlj.callsite
    • +
  • llvm.eh.sjlj.dispatchsetup
  • Asm Table Formats
      @@ -55,7 +58,7 @@ -
      Introduction
      +
      Introduction
      @@ -102,6 +105,38 @@
      + +
      + Setjmp/Longjmp Exception Handling +
      + +
      + +

      Setjmp/Longjmp (SJLJ) based exception handling uses LLVM intrinsics + llvm.eh.sjlj.setjmp and + llvm.eh.sjlj.longjmp to + handle control flow for exception handling.

      + +

      For each function which does exception processing, be it try/catch blocks + or cleanups, that function registers itself on a global frame list. When + exceptions are being unwound, the runtime uses this list to identify which + functions need processing.

      + +

      Landing pad selection is encoded in the call site entry of the function + context. The runtime returns to the function via + llvm.eh.sjlj.longjmp, where + a switch table transfers control to the appropriate landing pad based on + the index stored in the function context.

      + +

      In contrast to DWARF exception handling, which encodes exception regions + and frame information in out-of-line tables, SJLJ exception handling + builds and removes the unwind frame context at runtime. This results in + faster exception handling at the expense of slower execution when no + exceptions are thrown. As exceptions are, by their nature, intended for + uncommon code paths, DWARF exception handling is generally preferred to + SJLJ.

      +
      +
      Overview @@ -262,10 +297,17 @@
    1. __cxa_begin_catch takes a exception structure reference as an argument and returns the value of the exception object.
      2. -
    2. __cxa_end_catch takes a exception structure reference as an - argument. This function clears the exception from the exception space. - Note: a rethrow from within the catch may replace this call with - a __cxa_rethrow.
      3. +
    3. __cxa_end_catch takes no arguments. This function:

      +
        +
      1. Locates the most recently caught exception and decrements its handler + count,
        2. +
      2. Removes the exception from the "caught" stack if the handler count + goes to zero, and
        3. +
      3. Destroys the exception if the handler count goes to zero, and the + exception was not re-thrown by throw.
        4. +
      +

      Note: a rethrow from within the catch may replace this call with + a __cxa_rethrow.

      4. @@ -282,10 +324,10 @@ from the landing pad to clean up code and then to the first catch. Since the required clean up for each invoke in a try may be different (e.g. intervening constructor), there may be several landing pads for a given - try. If cleanups need to be run, the number zero should be passed as the + try. If cleanups need to be run, an i32 0 should be passed as the last llvm.eh.selector argument. - However for C++ a null i8* must - be passed instead.

      + However, when using DWARF exception handling with C++, a i8* null + must be passed instead.

      @@ -363,7 +405,7 @@ 
      -  i8* %llvm.eh.exception( )
+  i8* %llvm.eh.exception()

      This intrinsic returns a pointer to the exception structure.

      @@ -378,8 +420,7 @@ 
      -  i32 %llvm.eh.selector.i32(i8*, i8*, i8*, ...)
-  i64 %llvm.eh.selector.i64(i8*, i8*, i8*, ...)
+  i32 %llvm.eh.selector(i8*, i8*, ...)

      This intrinsic is used to compare the exception with the given type infos, @@ -411,8 +452,7 @@ 

      -  i32 %llvm.eh.typeid.for.i32(i8*)
-  i64 %llvm.eh.typeid.for.i64(i8*)
+  i32 %llvm.eh.typeid.for(i8*)

      This intrinsic returns the type info index in the exception table of the @@ -451,6 +491,26 @@

      + +
      + llvm.eh.sjlj.longjmp +
      + +
      + +
      +  void %llvm.eh.sjlj.setjmp(i8*)
+
      + +

      The llvm.eh.sjlj.longjmp + intrinsic is used to implement __builtin_longjmp() for SJLJ + style exception handling. The single parameter is a pointer to a + buffer populated by + llvm.eh.sjlj.setjmp. The frame pointer and stack pointer + are restored from the buffer, then control is transfered to the + destination address.

      + +
      llvm.eh.sjlj.lsda @@ -459,7 +519,7 @@ 
      -  i8* %llvm.eh.sjlj.lsda( )
+  i8* %llvm.eh.sjlj.lsda()

      Used for SJLJ based exception handling, the @@ -470,6 +530,41 @@

      + +
      + llvm.eh.sjlj.callsite +
      + +
      + +
      +  void %llvm.eh.sjlj.callsite(i32)
+
      + +

      For SJLJ based exception handling, the + llvm.eh.sjlj.callsite intrinsic identifies the callsite value + associated with the following invoke instruction. This is used to ensure + that landing pad entries in the LSDA are generated in the matching order.

      + +
      + + +
      + llvm.eh.sjlj.dispatchsetup +
      + +
      + +
      +  void %llvm.eh.sjlj.dispatchsetup(i32)
+
      + +

      For SJLJ based exception handling, the + llvm.eh.sjlj.dispatchsetup intrinsic is used by targets to do + any unwind-edge setup they need. By default, no action is taken.

      + +
      +
      Asm Table Formats