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authorSaleem Abdulrasool <compnerd@compnerd.org>2014-06-09 20:18:42 +0000
committerSaleem Abdulrasool <compnerd@compnerd.org>2014-06-09 20:18:42 +0000
commitc90ddb186967525c41456565152d7cd898616bda (patch)
tree568c491d221518a3d71bd81bc426d179c2058f9b /docs
parent8a0c2d17f5a26bde5e080abd88587aba76b6a325 (diff)
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ARM: add VLA extension for WoA Itanium ABI
The armv7-windows-itanium environment is nearly identical to the MSVC ABI. It has a few divergences, mostly revolving around the use of the Itanium ABI for C++. VLA support is one of the extensions that are amongst the set of the extensions. This adds support for proper VLA emission for this environment. This is somewhat similar to the handling for __chkstk emission on X86 and the large stack frame emission for ARM. The invocation style for chkstk is still controlled via the -mcmodel flag to clang. Make an explicit note that this is an extension. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210489 91177308-0d34-0410-b5e6-96231b3b80d8
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-rw-r--r--docs/Extensions.rst14
1 files changed, 14 insertions, 0 deletions
diff --git a/docs/Extensions.rst b/docs/Extensions.rst
index cd489c0e54..271c08598b 100644
--- a/docs/Extensions.rst
+++ b/docs/Extensions.rst
@@ -195,3 +195,17 @@ range via a slight deviation. It will generate an indirect jump as follows:
blx r12
sub.w sp, sp, r4
+Variable Length Arrays
+^^^^^^^^^^^^^^^^^^^^^^
+
+The reference implementation (Microsoft Visual Studio 2012) does not permit the
+emission of Variable Length Arrays (VLAs).
+
+The Windows ARM Itanium ABI extends the base ABI by adding support for emitting
+a dynamic stack allocation. When emitting a variable stack allocation, a call
+to ``__chkstk`` is emitted unconditionally to ensure that guard pages are setup
+properly. The emission of this stack probe emission is handled similar to the
+standard stack probe emission.
+
+The MSVC environment does not emit code for VLAs currently.
+