[Lldb-commits] [PATCH] 32-bit linux Remove WriteRegOperation's explicit GetAsUInt32() call

[Matthew Gardiner]

Hi folks

Even with the register map fixed (see UserArea in RegisterContextLinux_i386.cpp)
an assertion failure occurs:

$ lldb hello
Current executable set to 'hello' (i386).
(lldb) log enable linux ptrace
(lldb) run
operation ptrace(PTRACE_SETOPTIONS, 2667, (nil), 0x58, 0)=0 called from file /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/Linux/ProcessMonitor.cpp line 1456
Process 2667 launching
operation ptrace(PTRACE_TRACEME, 0, (nil), (nil), 0)=0 called from file /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/Linux/ProcessMonitor.cpp line 1196
operation ptrace(PTRACE_PEEKDATA, 2667, 0x8048340, (nil), 0)=895EED31 called from file /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/Linux/ProcessMonitor.cpp line 245
operation ptrace(PTRACE_PEEKDATA, 2667, 0x8048340, (nil), 0)=895EED31 called from file /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/Linux/ProcessMonitor.cpp line 245
operation ptrace(PTRACE_POKEDATA, 2667, 0x8048340, 0x895eedcc, 0)=0 called from file /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/Linux/ProcessMonitor.cpp line 319
operation ptrace(PTRACE_PEEKDATA, 2667, 0x8048340, (nil), 0)=895EEDCC called from file /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/Linux/ProcessMonitor.cpp line 245
operation ptrace(PTRACE_POKEUSER, 2667, 0x114, 0xffffffff, 0)=0 called from file /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/Linux/ProcessMonitor.cpp line 543
operation ptrace(PTRACE_POKEUSER, 2667, 0x118, 0xffffffff, 0)=0 called from file /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/Linux/ProcessMonitor.cpp line 543
operation ptrace(PTRACE_PEEKUSER, 2667, 0x114, (nil), 0)=FFFFFFFF called from file /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/Linux/ProcessMonitor.cpp line 494
operation ptrace(PTRACE_PEEKUSER, 2667, 0x114, (nil), 0)=FFFFFFFF called from file /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/Linux/ProcessMonitor.cpp line 494
operation ptrace(PTRACE_POKEUSER, 2667, 0x114, 0xffffffff, 0)=0 called from file /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/Linux/ProcessMonitor.cpp line 543
operation ptrace(PTRACE_PEEKUSER, 2667, 0x118, (nil), 0)=FFFFFFFF called from file /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/Linux/ProcessMonitor.cpp line 494
operation ptrace(PTRACE_PEEKUSER, 2667, 0xfc, (nil), 0)=0 called from file /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/Linux/ProcessMonitor.cpp line 494
lldb: /home/mg11/src/heracles/llvm/tools/lldb/source/Plugins/Process/POSIX/POSIXThread.cpp:530: void POSIXThread::WatchNotify(const ProcessMessage&): Assertion `wp_sp.get() && "No watchpoint found"' 
failed.
Aborted (core dumped)

The root cause of this is that 0xffffffff is written to dr6/7 originally from
RegisterContextPOSIXProcessMonitor_x86.cpp, whereas the programmer intended
0 to be written:

RegisterContextPOSIXProcessMonitor_x86_64::IsWatchpointHit(uint32_t hw_index)
{
<snip>
         RegisterValue zero_bits = RegisterValue(uint64_t(0));
         if (!WriteRegister(m_reg_info.first_dr + 6, zero_bits) || !WriteRegister(m_reg_info.first_dr + 7, zero_bits))

Construction of the RegisterValue as uint64_t and the subsequent conditional
compilation of 32-bit code within ProcessMonitor.cpp

void
WriteRegOperation::Execute(ProcessMonitor *monitor)
{
<snip>
#if __WORDSIZE == 32
     buf = (void*) m_value.GetAsUInt32();
#else

combined with RegisterValue's implementation returning "fail_value" for
wrapped 64-bit data accessed as 32-bits.

Removal of the preprocessing step, relies on the compiler forcing truncation
to 32-bit, when compiled on 32-bit platform, more faithfully than the
explicit GetAsUInt32().

Please could someone apply the attached patch which fixes the fail_value
return. I tested this on 32-bit by launching a program, stopping, setting
a break, then resuming it. It was fine. I can't test 64-bit yet, but clearly
my proposed patch results in the 64-bit code being unchanged.

Index: source/Plugins/Process/Linux/ProcessMonitor.cpp
===================================================================
--- source/Plugins/Process/Linux/ProcessMonitor.cpp	(revision 202675)
+++ source/Plugins/Process/Linux/ProcessMonitor.cpp	(working copy)
@@ -532,11 +532,7 @@
      void* buf;
      Log *log (ProcessPOSIXLog::GetLogIfAllCategoriesSet (POSIX_LOG_REGISTERS));

-#if __WORDSIZE == 32
-    buf = (void*) m_value.GetAsUInt32();
-#else
      buf = (void*) m_value.GetAsUInt64();
-#endif

      if (log)
          log->Printf ("ProcessMonitor::%s() reg %s: %p", __FUNCTION__, m_reg_name, buf);

thanks
Matt

PS

(If this patch is applied *and* the debug register offset problem fixed -
I'm uploading separate patch - then 32-bit linux debug experience is
sane).





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