[llvm-commits] [llvm] r97183 - /llvm/trunk/lib/CodeGen/AsmPrinter/DwarfException.cpp

[Bill Wendling]

Author: void
Date: Thu Feb 25 17:52:44 2010
New Revision: 97183

URL: http://llvm.org/viewvc/llvm-project?rev=97183&view=rev
Log:
Catch a corner case where adding the padding to the "TType base offset" field
will eliminate the need for padding in the "Call site table length". E.g., if
we have this:

    GCC_except_table1:
    Lexception1:
        .byte   0xff  ## @LPStart Encoding = omit
        .byte   0x9b  ## @TType Encoding = indirect pcrel sdata4
        .byte   0x7f  ## @TType base offset
        .byte   0x03  ## Call site Encoding = udata4
        .byte   0x89  ## Call site table length

with padding of 1. We want to emit the padding like this:
 
    GCC_except_table1:
    Lexception1:
        .byte   0xff  ## @LPStart Encoding = omit
        .byte   0x9b  ## @TType Encoding = indirect pcrel sdata4
        .byte   0xff  ## @TType base offset
        .space  1,0   ## Padding
        .byte   0x03  ## Call site Encoding = udata4
        .byte   0x89  ## Call site table length

and not with padding on the "Call site table length" entry.

Modified:
    llvm/trunk/lib/CodeGen/AsmPrinter/DwarfException.cpp

Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfException.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfException.cpp?rev=97183&r1=97182&r2=97183&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfException.cpp (original)
+++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfException.cpp Thu Feb 25 17:52:44 2010
@@ -745,10 +745,52 @@
     TTypeBaseOffset;                            // TType base offset
   unsigned SizeAlign = (4 - TotalSize) & 3;
 
-  if (HaveTTData)
+  if (HaveTTData) {
     // Account for any extra padded that will be added to the call site table
     // length.
-    EmitULEB128(TTypeBaseOffset + SizeAlign, "@TType base offset");
+    unsigned Offset = TTypeBaseOffset + SizeAlign;
+    unsigned OffsetSize = MCAsmInfo::getULEB128Size(Offset);
+    unsigned TTypeBaseOverflow = 0;
+
+    // If adding the extra alignment to the TType base offset makes the new
+    // value of TTypeBaseOffset overflow (i.e., go from encoded as 1 byte to 2
+    // bytes), then the padding needs to be smaller by that amount.
+    if (OffsetSize != TTypeBaseOffsetSize) {
+      assert((int)OffsetSize - (int)TTypeBaseOffsetSize);
+      TTypeBaseOverflow = OffsetSize - TTypeBaseOffsetSize;
+      assert(TTypeBaseOffsetSize >= SizeAlign);
+      SizeAlign -= TTypeBaseOverflow;
+    }
+
+    if (!TTypeBaseOverflow || SizeAlign != 0)
+      EmitULEB128(Offset, "@TType base offset");
+    else
+      // If adding the extra padding to this offset causes it to buffer to the
+      // size of the padding needed, then we should perform the padding here and
+      // not at the call site table below. E.g. if we have this:
+      //
+      //    GCC_except_table1:
+      //    Lexception1:
+      //        .byte   0xff  ## @LPStart Encoding = omit
+      //        .byte   0x9b  ## @TType Encoding = indirect pcrel sdata4
+      //        .byte   0x7f  ## @TType base offset
+      //        .byte   0x03  ## Call site Encoding = udata4
+      //        .byte   0x89  ## Call site table length
+      //
+      // with padding of 1. We want to emit the padding like this:
+      // 
+      //    GCC_except_table1:
+      //    Lexception1:
+      //        .byte   0xff  ## @LPStart Encoding = omit
+      //        .byte   0x9b  ## @TType Encoding = indirect pcrel sdata4
+      //        .byte   0xff  ## @TType base offset
+      //        .space  1,0   ## Padding
+      //        .byte   0x03  ## Call site Encoding = udata4
+      //        .byte   0x89  ## Call site table length
+      //
+      // and not with padding on the "Call site table length" entry.
+      EmitULEB128(TTypeBaseOffset, "@TType base offset", TTypeBaseOverflow);
+  }
 
   // SjLj Exception handling
   if (IsSJLJ) {