[X86] Add -mseparate-stack-seg

[mlemay-intel]

Summary

This patch adds the -mseparate-stack-seg option to enable restricting accesses to help prevent stack corruption.

[delena]

lib/CodeGen/TargetInfo.cpp

1569 ↗

(On Diff #47511)

Hi,
I'm not clang reviewer at all and you can ignore my comment.

Searching string looks strange for me. I suppose that this string should be defined in another form. Something like
options::OPT_separate_stack_seg.

1577 ↗

(On Diff #47511)

You should not use 258 as a constant. It should be defined somewhere as address space enum.

1578 ↗

(On Diff #47511)

This line alignment does not match LLVM style.

1580 ↗

(On Diff #47511)

Again, not sure that I'm right. You are trying to create addressspacecast. Is it the right way to create ptrtoint + inttoptr?

[mlemay-intel]

Thank you for your feedback!

lib/CodeGen/TargetInfo.cpp

1569 ↗

(On Diff #47511)

I haven't quite found an example of how an option like this should be handled. String comparisons of this form are performed in clang/lib/Basic/Targets.cpp, but there they are used to initialize variables. Furthermore, all of those tests are for CPU features, whereas this one is for a particular segment configuration.

1577 ↗

(On Diff #47511)

I agree with this principle. However, the address space numbers for FS and GS are listed in the Clang documentation [1] and are used as literals in LLVM code. Thus, I think this patch is consistent with existing usage of address space numbers.

[1] http://clang.llvm.org/docs/LanguageExtensions.html#memory-references-off-the-gs-segment

1578 ↗

(On Diff #47511)

I'll fix it.

1580 ↗

(On Diff #47511)

I first attempted to create an address space cast, but LLVM disallows that. I think it is necessary to perform the conversion through an int, but I am not entirely sure of that.

[qcolombet]

Hi Craig,

Could you have a look? I am not confident enough with clang to give more feedback than Elena.

Cheers,
-Quentin

[mlemay-intel]

Revise patch to fix line alignment.

[mkuper]

I really don't know enough about this part of clang either.

[mlemay-intel]

Removed the portions that are specific to 32-bit segmentation. I plan to resubmit those later as a separate patch.

include/clang/Driver/Options.td

 def mno_cx16 : Flag<["-"], "mno-cx16">, Group<m_x86_Features_Group>;
 def mno_fxsr : Flag<["-"], "mno-fxsr">, Group<m_x86_Features_Group>;
 def mno_xsave : Flag<["-"], "mno-xsave">, Group<m_x86_Features_Group>;
 def mno_xsaveopt : Flag<["-"], "mno-xsaveopt">, Group<m_x86_Features_Group>;
 def mno_xsavec : Flag<["-"], "mno-xsavec">, Group<m_x86_Features_Group>;
 def mno_xsaves : Flag<["-"], "mno-xsaves">, Group<m_x86_Features_Group>;
 def mno_mwaitx : Flag<["-"], "mno-mwaitx">, Group<m_x86_Features_Group>;
 def mno_pku : Flag<["-"], "mno-pku">, Group<m_x86_Features_Group>;
+def mno_separate_stack_seg : Flag<["-"], "mno-separate-stack-seg">, Group<m_x86_Features_Group>;
 
 def munaligned_access : Flag<["-"], "munaligned-access">, Group<m_arm_Features_Group>,
   HelpText<"Allow memory accesses to be unaligned (AArch32/AArch64 only)">;
 def mno_unaligned_access : Flag<["-"], "mno-unaligned-access">, Group<m_arm_Features_Group>,
   HelpText<"Force all memory accesses to be aligned (AArch32/AArch64 only)">;
 def mstrict_align : Flag<["-"], "mstrict-align">, Alias<mno_unaligned_access>, Flags<[CC1Option,HelpHidden]>,
   HelpText<"Force all memory accesses to be aligned (same as mno-unaligned-access)">;
 def mno_thumb : Flag<["-"], "mno-thumb">, Group<m_arm_Features_Group>;

 def mfma4 : Flag<["-"], "mfma4">, Group<m_x86_Features_Group>;
 def mfma : Flag<["-"], "mfma">, Group<m_x86_Features_Group>;
 def mxop : Flag<["-"], "mxop">, Group<m_x86_Features_Group>;
 def mf16c : Flag<["-"], "mf16c">, Group<m_x86_Features_Group>;
 def mrtm : Flag<["-"], "mrtm">, Group<m_x86_Features_Group>;
 def mprfchw : Flag<["-"], "mprfchw">, Group<m_x86_Features_Group>;
 def mrdseed : Flag<["-"], "mrdseed">, Group<m_x86_Features_Group>;
 def mpku : Flag<["-"], "mpku">, Group<m_x86_Features_Group>;
+def mseparate_stack_seg : Flag<["-"], "mseparate-stack-seg">, Group<m_x86_Features_Group>;
 def madx : Flag<["-"], "madx">, Group<m_x86_Features_Group>;
 def msha : Flag<["-"], "msha">, Group<m_x86_Features_Group>;
 def mcx16 : Flag<["-"], "mcx16">, Group<m_x86_Features_Group>;
 def mfxsr : Flag<["-"], "mfxsr">, Group<m_x86_Features_Group>;
 def mxsave : Flag<["-"], "mxsave">, Group<m_x86_Features_Group>;
 def mxsaveopt : Flag<["-"], "mxsaveopt">, Group<m_x86_Features_Group>;
 def mxsavec : Flag<["-"], "mxsavec">, Group<m_x86_Features_Group>;
 def mxsaves : Flag<["-"], "mxsaves">, Group<m_x86_Features_Group>;