[PATCH] D123427: Reset _unwindInfoMissing when info is found eventually

[Dimitry Andric via Phabricator via llvm-commits]

dim created this revision.
dim added reviewers: compnerd, jrtc27, ldionne, MaskRay, mstorsjo, nikic.
Herald added subscribers: libcxx-commits, StephenFan.
Herald added projects: libunwind, All.
Herald added a reviewer: libunwind.
dim requested review of this revision.
Herald added a project: LLVM.

As reported in https://github.com/llvm/llvm-project/issues/54799, when
using the C APIs `unw_init_local()`, `unw_set_reg()`, `unw_get_reg()`
and `unw_step()`, sometimes libunwind can erroneously conclude there is
no unwind info available.

This is because the initial call to `co->setInfoBasedOnIPRegister()` in
`unw_init_local()` can set `_unwindInfoMissing` to `true`, as at that
point there may not yet be unwind info available.

Subsequent calls to `unw_set_reg()`, with the register parameter set to
`UNW_REG_IP`, might still be able to find unwind info based on the new
IP value, but it does *not* reset `_unwindInfoMissing` to `false` in
those cases, so follow-up calls to `unw_step()` will erroneously return
`UNW_STEP_END` immediately.

To fix this, add explicit resets of `_unwindInfoMissing` to `false`, in
the various places where `setInfoBasedOnIPRegister()` actually does find
unwind info.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D123427

Files:
  libunwind/src/UnwindCursor.hpp


Index: libunwind/src/UnwindCursor.hpp
===================================================================
--- libunwind/src/UnwindCursor.hpp
+++ libunwind/src/UnwindCursor.hpp
@@ -1963,6 +1963,7 @@
         if ((sects.dwarf_section != 0) && compactSaysUseDwarf(&dwarfOffset)) {
           if (this->getInfoFromDwarfSection(pc, sects, dwarfOffset)) {
             // found info in dwarf, done
+            _unwindInfoMissing = false;
             return;
           }
         }
@@ -1978,8 +1979,10 @@
 
 #if defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
     // If there is SEH unwind info, look there next.
-    if (this->getInfoFromSEH(pc))
+    if (this->getInfoFromSEH(pc)) {
+      _unwindInfoMissing = false;
       return;
+    }
 #endif
 
 #if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
@@ -1987,6 +1990,7 @@
     if (sects.dwarf_section != 0) {
       if (this->getInfoFromDwarfSection(pc, sects)) {
         // found info in dwarf, done
+        _unwindInfoMissing = false;
         return;
       }
     }
@@ -1994,8 +1998,10 @@
 
 #if defined(_LIBUNWIND_ARM_EHABI)
     // If there is ARM EHABI unwind info, look there next.
-    if (sects.arm_section != 0 && this->getInfoFromEHABISection(pc, sects))
+    if (sects.arm_section != 0 && this->getInfoFromEHABISection(pc, sects)) {
+      _unwindInfoMissing = false;
       return;
+    }
 #endif
   }
 
@@ -2008,8 +2014,10 @@
     typename CFI_Parser<A>::FDE_Info fdeInfo;
     typename CFI_Parser<A>::CIE_Info cieInfo;
     if (!CFI_Parser<A>::decodeFDE(_addressSpace, cachedFDE, &fdeInfo, &cieInfo))
-      if (getInfoFromFdeCie(fdeInfo, cieInfo, pc, 0))
+      if (getInfoFromFdeCie(fdeInfo, cieInfo, pc, 0)) {
+        _unwindInfoMissing = false;
         return;
+      }
   }
 
   // Lastly, ask AddressSpace object about platform specific ways to locate
@@ -2021,8 +2029,10 @@
     if (!CFI_Parser<A>::decodeFDE(_addressSpace, fde, &fdeInfo, &cieInfo)) {
       // Double check this FDE is for a function that includes the pc.
       if ((fdeInfo.pcStart <= pc) && (pc < fdeInfo.pcEnd))
-        if (getInfoFromFdeCie(fdeInfo, cieInfo, pc, 0))
+        if (getInfoFromFdeCie(fdeInfo, cieInfo, pc, 0)) {
+          _unwindInfoMissing = false;
           return;
+        }
     }
   }
 #endif // #if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)


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