[PATCH][X86_64/MC] Fix alignment of unwind data.

Kai Nacke kai.nacke at redstar.de
Sun Sep 15 10:57:10 PDT 2013


Hi!

The current alignment in the SEH unwind data does not correspond to the 
MS specification.

For alignment purposes, the instruction array will always have an even
number of entries, with the final entry potentially unused (in which 
case the array will be one longer than indicated by the count of unwind 
codes field).

The attached patch changes the alignment as required by the spec.

Again, this patch was already reviewed by Charles Davis and Nico Rieck 
on 07/03 but I miss the final approval from the code owners.

Regards
Kai
-------------- next part --------------
>From 6636ae353009527cc15af4e7a0f0dae327b59ee2 Mon Sep 17 00:00:00 2001
From: kai <kai at redstar.de>
Date: Tue, 28 May 2013 06:37:39 +0200
Subject: [PATCH 1/1] Fix alignment of unwind data.

For alignment purposes, the instruction array will always have an even
number of entries, with the final entry potentially unused (in which case

the array will be one longer than indicated by the count of unwind codes

field).
---
 lib/MC/MCWin64EH.cpp      | 19 +++++++----
 test/MC/COFF/seh-align1.s | 65 +++++++++++++++++++++++++++++++++++++
 test/MC/COFF/seh-align2.s | 78 ++++++++++++++++++++++++++++++++++++++++++++
 test/MC/COFF/seh-align3.s | 83 +++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 238 insertions(+), 7 deletions(-)
 create mode 100644 test/MC/COFF/seh-align1.s
 create mode 100644 test/MC/COFF/seh-align2.s
 create mode 100644 test/MC/COFF/seh-align3.s

diff --git a/lib/MC/MCWin64EH.cpp b/lib/MC/MCWin64EH.cpp
index c3d568b..b8b07d3 100644
--- a/lib/MC/MCWin64EH.cpp
+++ b/lib/MC/MCWin64EH.cpp
@@ -159,11 +159,11 @@ static void EmitUnwindInfo(MCStreamer &streamer, MCWin64EHUnwindInfo *info) {

   MCContext &context = streamer.getContext();
   streamer.EmitValueToAlignment(4);
-  // Upper 3 bits are the version number (currently 1).
-  uint8_t flags = 0x01;
   info->Symbol = context.CreateTempSymbol();
   streamer.EmitLabel(info->Symbol);

+  // Upper 3 bits are the version number (currently 1).
+  uint8_t flags = 0x01;
   if (info->ChainedParent)
     flags |= Win64EH::UNW_ChainInfo << 3;
   else {
@@ -199,6 +199,14 @@ static void EmitUnwindInfo(MCStreamer &streamer, MCWin64EHUnwindInfo *info) {
     EmitUnwindCode(streamer, info->Begin, inst);
   }

+  // For alignment purposes, the instruction array will always have an even
+  // number of entries, with the final entry potentially unused (in which case
+  // the array will be one longer than indicated by the count of unwind codes
+  // field).
+  if (numCodes & 1) {
+    streamer.EmitIntValue(0, 2);
+  }
+
   if (flags & (Win64EH::UNW_ChainInfo << 3))
     EmitRuntimeFunction(streamer, info->ChainedParent);
   else if (flags &
@@ -206,14 +214,11 @@ static void EmitUnwindInfo(MCStreamer &streamer, MCWin64EHUnwindInfo *info) {
     streamer.EmitValue(MCSymbolRefExpr::Create(info->ExceptionHandler,
                                               MCSymbolRefExpr::VK_COFF_IMGREL32,
                                               context), 4);
-  else if (numCodes < 2) {
+  else if (numCodes == 0) {
     // The minimum size of an UNWIND_INFO struct is 8 bytes. If we're not
     // a chained unwind info, if there is no handler, and if there are fewer
     // than 2 slots used in the unwind code array, we have to pad to 8 bytes.
-    if (numCodes == 1)
-      streamer.EmitIntValue(0, 2);
-    else
-      streamer.EmitIntValue(0, 4);
+    streamer.EmitIntValue(0, 4);
   }
 }

diff --git a/test/MC/COFF/seh-align1.s b/test/MC/COFF/seh-align1.s
new file mode 100644
index 0000000..aafc6ed
--- /dev/null
+++ b/test/MC/COFF/seh-align1.s
@@ -0,0 +1,65 @@
+// This test checks the alignment and padding of the unwind info.
+
+// RUN: llvm-mc -triple x86_64-pc-win32 -filetype=obj %s | llvm-readobj -s -sd -sr -u | FileCheck %s
+
+// CHECK:      Sections [
+// CHECK:        Section {
+// CHECK:          Name: .xdata
+// CHECK:          RawDataSize: 8
+// CHECK:          RelocationCount: 0
+// CHECK:          Characteristics [
+// CHECK-NEXT:       ALIGN_4BYTES
+// CHECK-NEXT:       CNT_INITIALIZED_DATA
+// CHECK-NEXT:       MEM_READ
+// CHECK-NEXT:     ]
+// CHECK:          Relocations [
+// CHECK-NEXT:     ]
+// CHECK:          SectionData (
+// CHECK-NEXT:       0000: 01000000 00000000
+// CHECK-NEXT:     )
+// CHECK-NEXT:   }
+// CHECK:        Section {
+// CHECK:          Name: .pdata
+// CHECK:          RawDataSize: 12
+// CHECK:          RelocationCount: 3
+// CHECK:          Characteristics [
+// CHECK-NEXT:       IMAGE_SCN_ALIGN_4BYTES
+// CHECK-NEXT:       IMAGE_SCN_CNT_INITIALIZED_DATA
+// CHECK-NEXT:       IMAGE_SCN_MEM_READ
+// CHECK-NEXT:     ]
+// CHECK:          Relocations [
+// CHECK-NEXT:       [[BeginDisp:0x[A-F0-9]+]] IMAGE_REL_AMD64_ADDR32NB smallFunc
+// CHECK-NEXT:       [[EndDisp:0x[A-F0-9]+]] IMAGE_REL_AMD64_ADDR32NB smallFunc
+// CHECK-NEXT:       [[UnwindDisp:0x[A-F0-9]+]] IMAGE_REL_AMD64_ADDR32NB .xdata
+// CHECK-NEXT:     ]
+// CHECK:          SectionData (
+// CHECK-NEXT:       0000: 00000000 01000000 00000000
+// CHECK-NEXT:     )
+// CHECK-NEXT:   }
+// CHECK:        UnwindInformation [
+// CHECK-NEXT:     RuntimeFunction {
+// CHECK-NEXT:     StartAddress: smallFunc {{(\+0x[A-F0-9]+ )?}}([[BeginDisp]])
+// CHECK-NEXT:     EndAddress: smallFunc {{(\+0x[A-F0-9]+ )?}}([[EndDisp]])
+// CHECK-NEXT:     UnwindInfoAddress: .xdata {{(\+0x[A-F0-9]+ )?}}([[UnwindDisp]])
+// CHECK-NEXT:     UnwindInfo {
+// CHECK-NEXT:       Version: 1
+// CHECK-NEXT:       Flags [
+// CHECK-NEXT:       ]
+// CHECK-NEXT:       PrologSize: 0
+// CHECK-NEXT:       FrameRegister: -
+// CHECK-NEXT:       FrameOffset: -
+// CHECK-NEXT:       UnwindCodeCount: 0
+// CHECK-NEXT:       UnwindCodes [
+// CHECK-NEXT:       ]
+// CHECK-NEXT:     }
+// CHECK-NEXT:   }
+// CHECK-NEXT: ]
+
+// Generate the minimal unwind info.
+// It contains only the version set to 1. All other bytes are 0.
+    .globl smallFunc
+    .def smallFunc; .scl 2; .type 32; .endef
+    .seh_proc smallFunc
+smallFunc:
+    ret
+    .seh_endproc
diff --git a/test/MC/COFF/seh-align2.s b/test/MC/COFF/seh-align2.s
new file mode 100644
index 0000000..5e6c49a
--- /dev/null
+++ b/test/MC/COFF/seh-align2.s
@@ -0,0 +1,78 @@
+// This test checks the alignment and padding of the unwind info.
+
+// RUN: llvm-mc -triple x86_64-pc-win32 -filetype=obj %s | llvm-readobj -s -sd -sr -u | FileCheck %s
+
+// CHECK:      Sections [
+// CHECK:        Section {
+// CHECK:          Name: .xdata
+// CHECK:          RawDataSize: 16
+// CHECK:          RelocationCount: 1
+// CHECK:          Characteristics [
+// CHECK-NEXT:       ALIGN_4BYTES
+// CHECK-NEXT:       CNT_INITIALIZED_DATA
+// CHECK-NEXT:       MEM_READ
+// CHECK-NEXT:     ]
+// CHECK:          Relocations [
+// CHECK-NEXT:       [[HandlerDisp:0x[A-F0-9]+]] IMAGE_REL_AMD64_ADDR32NB __C_specific_handler
+// CHECK-NEXT:     ]
+// CHECK:          SectionData (
+// CHECK-NEXT:       0000: 09000100 04220000 00000000 BEBAFECA
+// CHECK-NEXT:     )
+// CHECK-NEXT:   }
+// CHECK-NEXT:   Section {
+// CHECK:          Name: .pdata
+// CHECK:          RawDataSize: 12
+// CHECK:          RelocationCount: 3
+// CHECK:          Characteristics [
+// CHECK-NEXT:       IMAGE_SCN_ALIGN_4BYTES
+// CHECK-NEXT:       IMAGE_SCN_CNT_INITIALIZED_DATA
+// CHECK-NEXT:       IMAGE_SCN_MEM_READ
+// CHECK-NEXT:     ]
+// CHECK:          Relocations [
+// CHECK-NEXT:       [[BeginDisp:0x[A-F0-9]+]] IMAGE_REL_AMD64_ADDR32NB func
+// CHECK-NEXT:       [[EndDisp:0x[A-F0-9]+]] IMAGE_REL_AMD64_ADDR32NB func
+// CHECK-NEXT:       [[UnwindDisp:0x[A-F0-9]+]] IMAGE_REL_AMD64_ADDR32NB .xdata
+// CHECK-NEXT:     ]
+// CHECK:          SectionData (
+// CHECK-NEXT:       0000: FCFFFFFF 05000000 00000000
+// CHECK-NEXT:     )
+// CHECK-NEXT:   }
+// CHECK-NEXT: ]
+// CHECK:      UnwindInformation [
+// CHECK-NEXT:   RuntimeFunction {
+// CHECK-NEXT:     StartAddress: func {{(\+0x[A-F0-9]+ )?}}([[BeginDisp]])
+// CHECK-NEXT:     EndAddress: func {{(\+0x[A-F0-9]+ )?}}([[EndDisp]])
+// CHECK-NEXT:     UnwindInfoAddress: .xdata {{(\+0x[A-F0-9]+ )?}}([[UnwindDisp]])
+// CHECK-NEXT:     UnwindInfo {
+// CHECK-NEXT:       Version: 1
+// CHECK-NEXT:       Flags [
+// CHECK-NEXT:         ExceptionHandler
+// CHECK-NEXT:       ]
+// CHECK-NEXT:       PrologSize: 0
+// CHECK-NEXT:       FrameRegister: -
+// CHECK-NEXT:       FrameOffset: -
+// CHECK-NEXT:       UnwindCodeCount: 1
+// CHECK-NEXT:       UnwindCodes [
+// CHECK-NEXT:         0x04: ALLOC_SMALL size=24
+// CHECK-NEXT:       ]
+// CHECK-NEXT:       Handler: __C_specific_handler ([[HandlerDisp]])
+// CHECK-NEXT:     }
+// CHECK-NEXT:   }
+// CHECK-NEXT: ]
+
+// Generates only one unwind code.
+// Requires padding of the unwind code array.
+    .globl func
+    .def func; .scl 2; .type 32; .endef
+    .seh_proc func
+    subq $24, %rsp
+    .seh_stackalloc 24
+    .seh_handler __C_specific_handler, @except
+    .seh_handlerdata
+    .long 0xcafebabe
+    .text
+    .seh_endprologue
+func:
+    addq $24, %rsp
+    ret
+    .seh_endproc
diff --git a/test/MC/COFF/seh-align3.s b/test/MC/COFF/seh-align3.s
new file mode 100644
index 0000000..238b5de
--- /dev/null
+++ b/test/MC/COFF/seh-align3.s
@@ -0,0 +1,83 @@
+// This test checks the alignment and padding of the unwind info.
+
+// RUN: llvm-mc -triple x86_64-pc-win32 -filetype=obj %s | llvm-readobj -s -sd -sr -u | FileCheck %s
+
+// CHECK:      Sections [
+// CHECK:        Section {
+// CHECK:          Name: .xdata
+// CHECK:          RawDataSize: 16
+// CHECK:          RelocationCount: 1
+// CHECK:          Characteristics [
+// CHECK-NEXT:       ALIGN_4BYTES
+// CHECK-NEXT:       CNT_INITIALIZED_DATA
+// CHECK-NEXT:       MEM_READ
+// CHECK-NEXT:     ]
+// CHECK:          Relocations [
+// CHECK-NEXT:       [[HandlerDisp:0x[A-F0-9]+]] IMAGE_REL_AMD64_ADDR32NB __C_specific_handler
+// CHECK-NEXT:     ]
+// CHECK:          SectionData (
+// CHECK-NEXT:       0000: 19000200 04D002C0 00000000 BEBAFECA
+// CHECK-NEXT:     )
+// CHECK-NEXT:   }
+// CHECK-NEXT:   Section {
+// CHECK:          Name: .pdata
+// CHECK:          RawDataSize: 12
+// CHECK:          RelocationCount: 3
+// CHECK:          Characteristics [
+// CHECK-NEXT:       IMAGE_SCN_ALIGN_4BYTES
+// CHECK-NEXT:       IMAGE_SCN_CNT_INITIALIZED_DATA
+// CHECK-NEXT:       IMAGE_SCN_MEM_READ
+// CHECK-NEXT:     ]
+// CHECK:          Relocations [
+// CHECK-NEXT:       [[BeginDisp:0x[A-F0-9]+]] IMAGE_REL_AMD64_ADDR32NB func
+// CHECK-NEXT:       [[EndDisp:0x[A-F0-9]+]] IMAGE_REL_AMD64_ADDR32NB func
+// CHECK-NEXT:       [[UnwindDisp:0x[A-F0-9]+]] IMAGE_REL_AMD64_ADDR32NB .xdata
+// CHECK-NEXT:     ]
+// CHECK:          SectionData (
+// CHECK-NEXT:       0000: FCFFFFFF 05000000 00000000
+// CHECK-NEXT:     )
+// CHECK-NEXT:   }
+// CHECK-NEXT: ]
+// CHECK:      UnwindInformation [
+// CHECK-NEXT:   RuntimeFunction {
+// CHECK-NEXT:     StartAddress: func {{(\+0x[A-F0-9]+ )?}}([[BeginDisp]])
+// CHECK-NEXT:     EndAddress: func {{(\+0x[A-F0-9]+ )?}}([[EndDisp]])
+// CHECK-NEXT:     UnwindInfoAddress: .xdata {{(\+0x[A-F0-9]+ )?}}([[UnwindDisp]])
+// CHECK-NEXT:     UnwindInfo {
+// CHECK-NEXT:       Version: 1
+// CHECK-NEXT:       Flags [
+// CHECK-NEXT:         ExceptionHandler
+// CHECK-NEXT:         TerminateHandler
+// CHECK-NEXT:       ]
+// CHECK-NEXT:       PrologSize: 0
+// CHECK-NEXT:       FrameRegister: -
+// CHECK-NEXT:       FrameOffset: -
+// CHECK-NEXT:       UnwindCodeCount: 2
+// CHECK-NEXT:       UnwindCodes [
+// CHECK-NEXT:         0x04: PUSH_NONVOL reg=R13
+// CHECK-NEXT:         0x02: PUSH_NONVOL reg=R12
+// CHECK-NEXT:       ]
+// CHECK-NEXT:       Handler: __C_specific_handler ([[HandlerDisp]])
+// CHECK-NEXT:     }
+// CHECK-NEXT:   }
+// CHECK-NEXT: ]
+
+// Generates two unwind codes.
+// Requires no padding of the unwind code array.
+    .globl func
+    .def func; .scl 2; .type 32; .endef
+    .seh_proc func
+    push %r12
+    .seh_pushreg 12
+    push %r13
+    .seh_pushreg 13
+    .seh_handler __C_specific_handler, @except, @unwind
+    .seh_handlerdata
+    .long 0xcafebabe
+    .text
+    .seh_endprologue
+func:
+    pop %r13
+    pop %r12
+    ret
+    .seh_endproc
--
1.8.0.msysgit.0



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