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

[Todd Fiala]

This is now in as part of r202887.


On Tue, Mar 4, 2014 at 2:22 AM, Matthew Gardiner <mg11 at csr.com> wrote:

> 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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-- 
Todd Fiala | Software Engineer | tfiala at google.com | 650-943-3180
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