[lldb-dev] [PATCH] 32-bit linux use hard-coded DR0 offset not offsetof against a structure

[Matthew Gardiner]

Hi folks

I'm posting this to dev not commits as it's slightly contentious, but when
combined with an earlier posting of mine:

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

this proposal fixes the 32-bit linux debug experience.

This patch proposes to calculate the offset of an i386 debug offset using a
simple base + multiple sum, instead using offsetof against a structure.

We all know that there are lots of ways to solve this problem. I'm posting this
one as it is compact and fits with the existing "#define DR_OFFSET(reg_index)"
pattern.

Index: source/Plugins/Process/POSIX/RegisterContextLinux_i386.cpp
===================================================================
--- source/Plugins/Process/POSIX/RegisterContextLinux_i386.cpp	(revision 202806)
+++ source/Plugins/Process/POSIX/RegisterContextLinux_i386.cpp	(working copy)
@@ -83,8 +83,9 @@
  };

  #define DR_SIZE sizeof(UserArea::u_debugreg[0])
+#define DR_0_OFFSET 0xFC
  #define DR_OFFSET(reg_index) \
-    (LLVM_EXTENSION offsetof(UserArea, u_debugreg[reg_index]))
+    (DR_0_OFFSET + (reg_index * 4))
  #define FPR_SIZE(reg) sizeof(((FPR_i386*)NULL)->reg)

  //---------------------------------------------------------------------------


Using the offsetof(struct, element) mantra can be problematic, if the underlying
structure is changed, and has no benefits IMO if the structure is not also used
as a structure.

Could someone apply this or a similar patch?

thanks
Matt




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