[libunwind] Support dwarf unwinding on i386 windows

[mstorsjo]

Summary

This builds on some parts from D33601 - some of them were commented on before. This patch contains comments and explanations about those non-obvious parts.

[rnk]

src/AddressSpace.hpp

388–389

".eh_frame" is 9 characters, right? I thought mingw linkers took sections with long names and moved them to an extended symbol table. Does that not apply to .eh_frame?

[mstorsjo]

src/AddressSpace.hpp

388–389

Yes, they do, so this actually only matches .eh_fram. I didn't yet look at how to navigate the IMAGE_*_HEADERS structs to find the coresponding full long name.

[jroelofs]

src/AddressSpace.hpp

521

Would it work to implement the win32 side of this via SymFromAddr?

src/UnwindRegistersRestore.S

29

Please invert the condition, and swap the if/else on this. That will make it more straightforward to adjust this for other platforms later.

[mstorsjo]

src/AddressSpace.hpp

521

Hmm, I guess that would work.

src/UnwindRegistersRestore.S

29

Ok, will do.

[rnk]

src/AddressSpace.hpp

388–389

Can you add a FIXME here? No need to read the long-form symbol table yet, I just want to document that we will need that for compatibility with ld.bfd.

[mstorsjo]

src/AddressSpace.hpp

521

... actually, I'm not sure how useful it is - it requires initializing the symbol handler with SymInitialize and point to a path to find the symbols. Plus that the symbol handler is single threaded and any calls to that would need to be guarded with a global mutex. So I think I'd defer that for now at least.

[mstorsjo]

Added a fixme comment about the truncated section name, flipped the ifdef in the assembly source. Didn't implement findFunctionName.

[jroelofs]

src/AddressSpace.hpp

521

alright, fine with me.

[mstorsjo]

docs/index.rst

53

FWIW, for this to actually work correct which this docs change claims, this also depends on D38680.

[mstorsjo]

Are there any further comments on this, or can someone of those who commented on it before approve it?

[jroelofs]

LGTM

[mstorsjo]

In D38679#894668, @jroelofs wrote:

LGTM

Thanks, will push this one without the docs update since it's still buggy in practice on windows until D38680 gets resolved.

docs/index.rst

 OS           Arch                 Compilers    Unwind Info
 ============ ==================== ============ ========================
 Mac OS X     i386, x86_64         Clang, GCC   DWARF CFI
 iOS          ARM                  Clang        SjLj
 Linux        i386, x86_64         Clang, GCC   DWARF CFI
 Linux        ARM                  Clang, GCC   EHABI
 Bare Metal   ARM                  Clang, GCC   EHABI
 NetBSD       x86_64               Clang, GCC   DWARF CFI
+Windows      i386                 Clang        DWARF CFI
 Any          i386, x86_64, ARM    Clang        SjLj
 ============ ==================== ============ ========================
 
 The following minimum compiler versions are strongly recommended.
 
 * Clang 3.5 and above
 * GCC 4.7 and above.
 

src/AddressSpace.hpp

 #ifndef __ADDRESSSPACE_HPP__
 #define __ADDRESSSPACE_HPP__
 
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
-#ifndef _LIBUNWIND_IS_BAREMETAL
+#if !defined(_LIBUNWIND_IS_BAREMETAL) && !defined(_WIN32)
 #include <dlfcn.h>
 #endif
 
 #ifdef __APPLE__
 #include <mach-o/getsect.h>
 namespace libunwind {
    bool checkKeyMgrRegisteredFDEs(uintptr_t targetAddr, void *&fde);
 }

 
 #elif defined(_LIBUNWIND_ARM_EHABI) || defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
 
 // ELF-based systems may use dl_iterate_phdr() to access sections
 // containing unwinding information. The ElfW() macro for pointer-size
 // independent ELF header traversal is not provided by <link.h> on some
 // systems (e.g., FreeBSD). On these systems the data structures are
 // just called Elf_XXX. Define ElfW() locally.
+#ifndef _WIN32
 #include <link.h>
+#else
+#include <windows.h>
+#include <psapi.h>
+#endif
 #if !defined(ElfW)
 #define ElfW(type) Elf_##type
 #endif
 
 #endif
 
 namespace libunwind {
 

 #elif defined(_LIBUNWIND_ARM_EHABI) && defined(_LIBUNWIND_IS_BAREMETAL)
   // Bare metal is statically linked, so no need to ask the dynamic loader
   info.arm_section =        (uintptr_t)(&__exidx_start);
   info.arm_section_length = (uintptr_t)(&__exidx_end - &__exidx_start);
   _LIBUNWIND_TRACE_UNWINDING("findUnwindSections: section %X length %x",
                              info.arm_section, info.arm_section_length);
   if (info.arm_section && info.arm_section_length)
     return true;
+#elif defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) && defined(_WIN32)
+  HMODULE mods[1024];
+  HANDLE process = GetCurrentProcess();
+  DWORD needed;
+
+  if (!EnumProcessModules(process, mods, sizeof(mods), &needed))
+    return false;
+
+  for (unsigned i = 0; i < (needed / sizeof(HMODULE)); i++) {
+    PIMAGE_DOS_HEADER pidh = (PIMAGE_DOS_HEADER)mods[i];
+    PIMAGE_NT_HEADERS pinh = (PIMAGE_NT_HEADERS)((BYTE *)pidh + pidh->e_lfanew);
+    PIMAGE_FILE_HEADER pifh = (PIMAGE_FILE_HEADER)&pinh->FileHeader;
+    PIMAGE_SECTION_HEADER pish = IMAGE_FIRST_SECTION(pinh);
+    bool found_obj = false;
+    bool found_hdr = false;
+
+    info.dso_base = (uintptr_t)mods[i];
+    for (unsigned j = 0; j < pifh->NumberOfSections; j++, pish++) {
+      uintptr_t begin = pish->VirtualAddress + (uintptr_t)mods[i];
+      uintptr_t end = begin + pish->Misc.VirtualSize;
+      if (!strncmp((const char *)pish->Name, ".text",
+                   IMAGE_SIZEOF_SHORT_NAME)) {
+        if (targetAddr >= begin && targetAddr < end)
+          found_obj = true;
+      } else if (!strncmp((const char *)pish->Name, ".eh_frame",
+                          IMAGE_SIZEOF_SHORT_NAME)) {
+        info.dwarf_section = begin;
+        info.dwarf_section_length = pish->Misc.VirtualSize;
+        found_hdr = true;
+      }
+      if (found_obj && found_hdr)
+        return true;
+    }
+  }
+  return false;
 #elif defined(_LIBUNWIND_ARM_EHABI) || defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
   struct dl_iterate_cb_data {
     LocalAddressSpace *addressSpace;
     UnwindInfoSections *sects;
     uintptr_t targetAddr;
   };
 
   dl_iterate_cb_data cb_data = {this, &info, targetAddr};
#else
   (void)fde;
   return false;
 #endif
 }
 
 inline bool LocalAddressSpace::findFunctionName(pint_t addr, char *buf,
                                                 size_t bufLen,
                                                 unw_word_t *offset) {
-#ifndef _LIBUNWIND_IS_BAREMETAL
+#if !defined(_LIBUNWIND_IS_BAREMETAL) && !defined(_WIN32)
   Dl_info dyldInfo;
   if (dladdr((void *)addr, &dyldInfo)) {
     if (dyldInfo.dli_sname != NULL) {
       snprintf(buf, bufLen, "%s", dyldInfo.dli_sname);
       *offset = (addr - (pint_t) dyldInfo.dli_saddr);
       return true;
     }
   }

src/UnwindRegistersRestore.S

 # On entry:
 #  +                       +
 #  +-----------------------+
 #  + thread_state pointer  +
 #  +-----------------------+
 #  + return address        +
 #  +-----------------------+   <-- SP
 #  +                       +
+#if !defined(_WIN32)
   movl   4(%esp), %eax
+#else
+  # On windows, the 'this' pointer is passed in ecx instead of on the stack
+  movl   %ecx, %eax
+#endif
   # set up eax and ret on new stack location
   movl  28(%eax), %edx # edx holds new stack pointer
   subl  $8,%edx
   movl  %edx, 28(%eax)
   movl  0(%eax), %ebx
   movl  %ebx, 0(%edx)
   movl  40(%eax), %ebx
   movl  %ebx, 4(%edx)

src/assembly.h

 #elif defined(__arm64__)
 #define SEPARATOR %%
 #else
 #define SEPARATOR ;
 #endif
 
 #if defined(__APPLE__)
 #define HIDDEN_DIRECTIVE .private_extern
+#elif defined(_WIN32)
+// In the COFF object file format, there's no attributes for a global,
+// non-static symbol to make it somehow hidden. So on windows, we don't
+// want to set this at all. To avoid conditionals in
+// DEFINE_LIBUNWIND_PRIVATE_FUNCTION below, make it .globl (which it already
+// is, defined in the same DEFINE_LIBUNWIND_PRIVATE_FUNCTION macro; the
+// duplicate .globl directives are harmless).
+#define HIDDEN_DIRECTIVE .globl
 #else
 #define HIDDEN_DIRECTIVE .hidden
 #endif
 
 #define GLUE2(a, b) a ## b
 #define GLUE(a, b) GLUE2(a, b)
 #define SYMBOL_NAME(name) GLUE(__USER_LABEL_PREFIX__, name)
 

src/config.h

 // Platform specific configuration defines.
 #ifdef __APPLE__
   #if defined(FOR_DYLD)
     #define _LIBUNWIND_SUPPORT_COMPACT_UNWIND
   #else
     #define _LIBUNWIND_SUPPORT_COMPACT_UNWIND
     #define _LIBUNWIND_SUPPORT_DWARF_UNWIND   1
   #endif
+#elif defined(_WIN32)
+  #define _LIBUNWIND_SUPPORT_DWARF_UNWIND 1
 #else
   #if defined(__ARM_DWARF_EH__) || !defined(__arm__)
     #define _LIBUNWIND_SUPPORT_DWARF_UNWIND 1
     #define _LIBUNWIND_SUPPORT_DWARF_INDEX 1
   #endif
 #endif
 
 #if defined(_LIBUNWIND_DISABLE_VISIBILITY_ANNOTATIONS)