Patch from Andrew Kaylor for linux:

The attached patch adds support for debugging 32-bit processes when running a 64-bit lldb on an x86_64 Linux system.
 
Making this work required two basic changes:
 
1)      Getting lldb to report that it could debug 32-bit processes
2)      Changing an assumption about how ptrace works when debugging cross-platform
 
For the first change, I took a conservative approach and only enabled this for x86_64 Linux platforms.  It may be that the change I made in Host.cpp could be extended to other 64-bit Linux platforms, but I'm not familiar enough with the other platforms to know for sure.
 
For the second change, the Linux ProcessMonitor class was assuming that ptrace(PTRACE_[PEEK|POKE]DATA...) would read/write a "word" based on the child process word size.  However, the ptrace documentation says that the "word" size read or written is "determined by the OS variant."  I verified experimentally that when ptracing a 32-bit child from a 64-bit parent a 64-bit word is read or written.

llvm-svn: 163398

1 files changed, 11 insertions, 0 deletions

diff --git a/lldb/source/Plugins/Platform/Linux/PlatformLinux.cpp b/lldb/source/Plugins/Platform/Linux/PlatformLinux.cpp
index 5cda1edd3c7..8d4ef495836 100644
--- a/lldb/source/Plugins/Platform/Linux/PlatformLinux.cpp
+++ b/lldb/source/Plugins/Platform/Linux/PlatformLinux.cpp
@@ -312,6 +312,17 @@ PlatformLinux::GetSupportedArchitectureAtIndex (uint32_t idx, ArchSpec &arch)
         arch = Host::GetArchitecture (Host::eSystemDefaultArchitecture);
         return arch.IsValid();
     }
+    else if (idx == 1)
+    {
+        // If the default host architecture is 64-bit, look for a 32-bit variant
+        ArchSpec hostArch
+                      = Host::GetArchitecture(Host::eSystemDefaultArchitecture);
+        if (hostArch.IsValid() && hostArch.GetTriple().isArch64Bit())
+        {
+            arch = Host::GetArchitecture (Host::eSystemDefaultArchitecture32);
+            return arch.IsValid();
+        }
+    }
     return false;
 }