[llvm-commits] [PATCH] Start of support for __attribute__((ms_hook_prologue))

[Charles Davis]

On 10/25/10 12:16 AM, Michael Spencer wrote:
> On Sun, Oct 24, 2010 at 9:43 PM, Charles Davis <cdavis at mymail.mines.edu> wrote:
>> Hi,
>>
>> I thought that, while I wait for a response to my latest clang "patch"
>> on cfe-dev, I'd work on something else Wine-related.
>>
>> Microsoft's compiler has a switch, '/hotpatch', that inserts a magic
>> sequence in the beginning of every compiled function. This sequence lets
>> other DLLs hook these functions (assuming they were exported from a DLL)
>> to do interesting things when they're called. In response, GCC added an
>> attribute, 'ms_hook_prologue', that does the same in GCC (partially at
>> the behest of the Wine developers). And now I intend to do the same for
>> Clang.
>>
>> Of course, this needs backend support. So, as with my
>> 'force_align_arg_pointer' patches, I'm starting with the basics. This
>> patch adds support for the attribute in LLVM IR. OK to commit?
>>
>> Chip
> 
> I'm not convinced that a new attribute is needed.
All right then, let me convince you.
> We already have
> dllexport linkage, so why not just add an option that makes all
> dllexport functions hot patchable? It doesn't change the calling
> convention at all.
Several reasons:
- This adds some noop instruction(s) to the beginning of the function.
(On x86, it adds a 'mov %edi,%edi'.) This could potentially affect
performance if the function is called over and over again. Are you sure
you want all dllexport functions to be hotpatchable?
- Not everyone uses dllexport. Some people still use .def files. Wine is
one notable example (though the .def files are autogenerated). They
declare some of their functions with this attribute.
- GCC already has this attribute. It's too late.
> 
> Also, this doesn't seem to include the lexing or parsing code for the keyword.
It was only missing the lexing code. Patch reattached.
> 
> - Michael Spencer

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