Modify split CallSiteRanges to use correct lengths

[modimo]

Summary

In D73739 @MaskRay pointed out that the lengths for CallSiteRanges in .gcc_except_table are not quite correct if blocks are outlined or using basic-block-sections. At runtime this is fine because the .eh_frame data will limit a function to a particular LSDA entry so that even though the longer length allows buffer-overflow the code length in .eh_frame acts as a back-stop.

However, in post-binary analysis tools (e.g. BOLT) that may only parse the .gcc_except_table section having these lengths be incorrect will result in a buffer overflow when using this field to read forward.

There's no binary cost for making these labels correct and leads to smaller offsets which compress better leading to very minor metadata size reduction.

Testing:
ninja check

[modimo]

Remove useless "if"

[MaskRay]

Unfortunately this does not work. The idea of D73739 is that all call site tables share the same action table. For each call site table, the action record offset of any call site entry is related to action_table_end. All call site tables need to share the same action_table_end. The weird thing is that call site tables will appear to be overlapping because action_table_end is also used to compute the size of a call site table.

[modimo]

@MaskRay Ah the action table start is inferred as the end of the CST. Saves a pointer but shackles the implementation. These tables will be fairly small (effectively 1 entry per "catch" in a function) and not all CST would need a corresponding action table (only those inside "try" do) so duplicating them is not as far-fetched as it would initially sound.

For my purposes though, the CST entries are guaranteed to be inclusive to the end of the function. Thus, at binary analysis level I can infer the end of the CST from the .eh_frame function length that points me there.

llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp

           if (S.Action == 0)
             Asm->OutStreamer->AddComment("  On action: cleanup");
           else
             Asm->OutStreamer->AddComment("  On action: " +
                                          Twine((S.Action - 1) / 2 + 1));
         }
         Asm->emitULEB128(S.Action);
       }
+
+      Asm->OutStreamer->emitLabel(CstEndLabel);
+
+      // With multiple call ranges, we need go generate multiple bases
+      CstEndLabel = Asm->createTempSymbol("action_table_base");
     }
-    Asm->OutStreamer->emitLabel(CstEndLabel);
   }
 
   // Emit the Action Table.
   int Entry = 0;
   for (SmallVectorImpl<ActionEntry>::const_iterator
          I = Actions.begin(), E = Actions.end(); I != E; ++I) {
     const ActionEntry &Action = *I;
 

llvm/test/CodeGen/X86/gcc_except_table_bb_sections.ll

 ; CHECK-NEXT:         .Lttbaseref0:
 ; CHECK-NEXT:           .byte 1                       # Call site Encoding = uleb128
 ; CHECK-NEXT:           .uleb128 .Laction_table_base0-.Lcst_begin0
 ; CHECK-NEXT:         .Lcst_begin0:
 ; CHECK-NEXT:           .uleb128 .Ltmp0-.Lfunc_begin0   # >> Call Site 1 <<
 ; CHECK-NEXT:           .uleb128 .Ltmp1-.Ltmp0          #   Call between .Ltmp0 and .Ltmp1
 ; CHECK-NEXT:           .uleb128 .Ltmp2-main.2          #     jumps to .Ltmp2
 ; CHECK-NEXT:           .byte 3                       #   On action: 2
+; CHECK-NEXT:         .Laction_table_base0
 ; CHECK-NEXT:           .p2align  2
 ; CHECK-NEXT:         .Lexception1:
 
 ; CHECK-NON-PIC-NEXT:   .byte 0                       # @LPStart Encoding = absptr
 ; CHECK-NON-PIC-NEXT:   .quad main.2
 
 ; CHECK-PIC-NEXT:       .byte 16                      # @LPStart Encoding = pcrel
 ; CHECK-PIC-NEXT:     [[DOT:\.Ltmp[0-9]+]]:
 ; CHECK-PIC-NEXT:       .quad main.2-[[DOT]]
 
 ; CHECK-NON-PIC-NEXT:   .byte 3                       # @TType Encoding = udata4
 
 ; CHECK-PIC-NEXT:       .byte 156                       # @TType Encoding = indirect pcrel sdata8
 
 ; CHECK-NEXT:           .uleb128 .Lttbase0-.Lttbaseref1
 ; CHECK-NEXT:         .Lttbaseref1:
 ; CHECK-NEXT:           .byte 1                       # Call site Encoding = uleb128
-; CHECK-NEXT:           .uleb128 .Laction_table_base0-.Lcst_begin1
+; CHECK-NEXT:           .uleb128 .Laction_table_base1-.Lcst_begin1
 ; CHECK-NEXT:         .Lcst_begin1:
+; CHECK-NEXT:         .Laction_table_base1
 ; CHECK-NEXT:           .p2align 2
 ; CHECK-NEXT:         .Lexception2:
 
 ; CHECK-NON-PIC-NEXT:   .byte 0                       # @LPStart Encoding = absptr
 ; CHECK-NON-PIC-NEXT:   .quad main.2
 
 ; CHECK-PIC-NEXT:       .byte 16                      # @LPStart Encoding = pcrel
 ; CHECK-PIC-NEXT:     [[DOT:\.Ltmp[0-9]+]]:
 ; CHECK-PIC-NEXT:       .quad main.2-[[DOT]]
 
 ; CHECK-NON-PIC-NEXT:   .byte 3                       # @TType Encoding = udata4
 
 ; CHECK-PIC-NEXT:       .byte 156                       # @TType Encoding = indirect pcrel sdata8
 
 ; CHECK-NEXT:           .uleb128 .Lttbase0-.Lttbaseref2
 ; CHECK-NEXT:         .Lttbaseref2:
 ; CHECK-NEXT:           .byte 1                       # Call site Encoding = uleb128
-; CHECK-NEXT:           .uleb128 .Laction_table_base0-.Lcst_begin2
+; CHECK-NEXT:           .uleb128 .Laction_table_base2-.Lcst_begin2
 ; CHECK-NEXT:         .Lcst_begin2:
 ; CHECK-NEXT:           .uleb128 main.2-main.2          # >> Call Site 2 <<
 ; CHECK-NEXT:           .uleb128 .LBB_END0_2-main.2     #   Call between main.2 and .LBB_END0_2
 ; CHECK-NEXT:           .byte 0                       #     has no landing pad
 ; CHECK-NEXT:           .byte 0                       #   On action: cleanup
-; CHECK-NEXT:         .Laction_table_base0:
+; CHECK-NEXT:         .Laction_table_base2:
 ; CHECK-NEXT:           .byte 0                       # >> Action Record 1 <<
 ; CHECK-NEXT:                                           #   Cleanup
 ; CHECK-NEXT:           .byte 0                       #   No further actions
 ; CHECK-NEXT:           .byte 1                       # >> Action Record 2 <<
 ; CHECK-NEXT:                                           #   Catch TypeInfo 1
 ; CHECK-NEXT:           .byte 125                     #   Continue to action 1
 ; CHECK-NEXT:           .p2align 2
 ; CHECK-NEXT:                                           # >> Catch TypeInfos <<

llvm/test/CodeGen/X86/gcc_except_table_bb_sections_ehpad_groups_with_cold.ll

 ; CHECK-NEXT:  .Lttbaseref0:
 ; CHECK-NEXT:    .byte  1                       # Call site Encoding = uleb128
 ; CHECK-NEXT:    .uleb128 .Laction_table_base0-.Lcst_begin0
 ; CHECK-NEXT:  .Lcst_begin0:
 ; CHECK-NEXT:    .uleb128 .Ltmp0-.Lfunc_begin0  # >> Call Site 1 <<
 ; CHECK-NEXT:    .uleb128 .Ltmp1-.Ltmp0         #   Call between .Ltmp0 and .Ltmp1
 ; CHECK-NEXT:    .uleb128 .Ltmp2-main.cold      #     jumps to .Ltmp2
 ; CHECK-NEXT:    .byte  3                       #   On action: 2
+; CHECK-NEXT:  .Laction_table_base0:
 ; CHECK-NEXT:    .p2align 2
 ; CHECK-NEXT:  .Lexception1:
 ; CHECK-NEXT:    .byte  0                       # @LPStart Encoding = absptr
 ; CHECK-NEXT:    .quad  main.cold
 ; CHECK-NEXT:    .byte  3                       # @TType Encoding = udata4
 ; CHECK-NEXT:    .uleb128 .Lttbase0-.Lttbaseref1
 ; CHECK-NEXT:  .Lttbaseref1:
 ; CHECK-NEXT:    .byte  1                       # Call site Encoding = uleb128
-; CHECK-NEXT:    .uleb128 .Laction_table_base0-.Lcst_begin1
+; CHECK-NEXT:    .uleb128 .Laction_table_base1-.Lcst_begin1
 ; CHECK-NEXT:  .Lcst_begin1:
 ; CHECK-NEXT:    .uleb128 main.cold-main.cold   # >> Call Site 2 <<
 ; CHECK-NEXT:    .uleb128 .LBB_END0_2-main.cold #   Call between main.cold and .LBB_END0_2
 ; CHECK-NEXT:    .byte  0                       #     has no landing pad
 ; CHECK-NEXT:    .byte  0                       #   On action: cleanup
-; CHECK-NEXT:  .Laction_table_base0:
+; CHECK-NEXT:  .Laction_table_base1:
 ; CHECK-NEXT:    .byte  0                       # >> Action Record 1 <<
 ; CHECK-NEXT:                                   #   Cleanup
 ; CHECK-NEXT:    .byte  0                       #   No further actions
 ; CHECK-NEXT:    .byte  1                       # >> Action Record 2 <<
 ; CHECK-NEXT:                                   #   Catch TypeInfo 1
 ; CHECK-NEXT:    .byte  125                     #   Continue to action 1
 ; CHECK-NEXT:    .p2align 2
 ; CHECK-NEXT:                                   # >> Catch TypeInfos <<
 ; CHECK-NEXT:    .long  _ZTIi                   # TypeInfo 1
 ; CHECK-NEXT:  .Lttbase0:
 ; CHECK-NEXT:    .p2align 2
 ; CHECK-NEXT:                                   # -- End function