[libcxx-commits] [PATCH] D111863: [libunwind] Add an interface for dynamic .eh_frame registration

[Peter S. Housel via Phabricator via libcxx-commits]

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The libgcc runtime library provides __register_frame and __deregister_frame functions, which can be used by dynamic code generators to register an .eh_frame section, which contains one or more Call Frame Information records, each consisting of a Common Information Entry record followed by one or more Frame Description Entry records. This libunwind library also provides __register_frame
and __deregister_frame functions, but they are effectively aliases for __unw_add_dynamic_fde and __unw_remove_dynamic_fde and thus can only take a single FDE.

This patch adds __unw_add_dynamic_eh_frame_section and __unw_remove_dynamic_eh_frame_section functions which explicitly use the .eh_frame format. Clients such as the ORCv2 platform and runtime can check for these functions and use them if unwinding is being
provided by libunwind, or fall back to __register_frame and __deregister_frame if unwinding is provided by libgcc.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D111863

Files:
  libunwind/src/DwarfParser.hpp
  libunwind/src/libunwind.cpp
  libunwind/src/libunwind_ext.h


Index: libunwind/src/libunwind_ext.h
===================================================================
--- libunwind/src/libunwind_ext.h
+++ libunwind/src/libunwind_ext.h
@@ -51,6 +51,9 @@
 extern void __unw_add_dynamic_fde(unw_word_t fde);
 extern void __unw_remove_dynamic_fde(unw_word_t fde);
 
+extern void __unw_add_dynamic_eh_frame_section(unw_word_t eh_frame_start);
+extern void __unw_remove_dynamic_eh_frame_section(unw_word_t eh_frame_start);
+
 #if defined(_LIBUNWIND_ARM_EHABI)
 extern const uint32_t* decode_eht_entry(const uint32_t*, size_t*, size_t*);
 extern _Unwind_Reason_Code _Unwind_VRS_Interpret(_Unwind_Context *context,
Index: libunwind/src/libunwind.cpp
===================================================================
--- libunwind/src/libunwind.cpp
+++ libunwind/src/libunwind.cpp
@@ -292,6 +292,35 @@
   // fde is own mh_group
   DwarfFDECache<LocalAddressSpace>::removeAllIn((LocalAddressSpace::pint_t)fde);
 }
+
+void __unw_add_dynamic_eh_frame_section(unw_word_t eh_frame_start) {
+  // The eh_frame section start serves as the mh_group
+  unw_word_t mh_group = eh_frame_start;
+  CFI_Parser<LocalAddressSpace>::CIE_Info cieInfo;
+  CFI_Parser<LocalAddressSpace>::FDE_Info fdeInfo;
+  auto p = (LocalAddressSpace::pint_t)eh_frame_start;
+  while (true) {
+    if (CFI_Parser<LocalAddressSpace>::decodeFDE(
+            LocalAddressSpace::sThisAddressSpace, p, &fdeInfo, &cieInfo,
+            true) == NULL) {
+      DwarfFDECache<LocalAddressSpace>::add((LocalAddressSpace::pint_t)mh_group,
+                                            fdeInfo.pcStart, fdeInfo.pcEnd,
+                                            fdeInfo.fdeStart);
+      p += fdeInfo.fdeLength;
+    } else if (CFI_Parser<LocalAddressSpace>::parseCIE(
+                   LocalAddressSpace::sThisAddressSpace, p, &cieInfo) == NULL) {
+      p += cieInfo.cieLength;
+    } else
+      return;
+  }
+}
+
+void __unw_remove_dynamic_eh_frame_section(unw_word_t eh_frame_start) {
+  // The eh_frame section start serves as the mh_group
+  DwarfFDECache<LocalAddressSpace>::removeAllIn(
+      (LocalAddressSpace::pint_t)eh_frame_start);
+}
+
 #endif // defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
 #endif // !defined(__USING_SJLJ_EXCEPTIONS__)
 
Index: libunwind/src/DwarfParser.hpp
===================================================================
--- libunwind/src/DwarfParser.hpp
+++ libunwind/src/DwarfParser.hpp
@@ -154,7 +154,8 @@
                       uintptr_t sectionLength, pint_t fdeHint, FDE_Info *fdeInfo,
                       CIE_Info *cieInfo);
   static const char *decodeFDE(A &addressSpace, pint_t fdeStart,
-                               FDE_Info *fdeInfo, CIE_Info *cieInfo);
+                               FDE_Info *fdeInfo, CIE_Info *cieInfo,
+                               bool useCIEInfo = false);
   static bool parseFDEInstructions(A &addressSpace, const FDE_Info &fdeInfo,
                                    const CIE_Info &cieInfo, pint_t upToPC,
                                    int arch, PrologInfo *results);
@@ -165,7 +166,8 @@
 /// Parse a FDE into a CIE_Info and an FDE_Info
 template <typename A>
 const char *CFI_Parser<A>::decodeFDE(A &addressSpace, pint_t fdeStart,
-                                     FDE_Info *fdeInfo, CIE_Info *cieInfo) {
+                                     FDE_Info *fdeInfo, CIE_Info *cieInfo,
+                                     bool useCIEInfo) {
   pint_t p = fdeStart;
   pint_t cfiLength = (pint_t)addressSpace.get32(p);
   p += 4;
@@ -181,9 +183,14 @@
     return "FDE is really a CIE"; // this is a CIE not an FDE
   pint_t nextCFI = p + cfiLength;
   pint_t cieStart = p - ciePointer;
-  const char *err = parseCIE(addressSpace, cieStart, cieInfo);
-  if (err != NULL)
-    return err;
+  if (useCIEInfo) {
+    if (cieInfo->cieStart != cieStart)
+      return "CIE start does not match";
+  } else {
+    const char *err = parseCIE(addressSpace, cieStart, cieInfo);
+    if (err != NULL)
+      return err;
+  }
   p += 4;
   // Parse pc begin and range.
   pint_t pcStart =


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