From c6a4f5e819217e1e12c458aed8e7b122e23a3a58 Mon Sep 17 00:00:00 2001 From: Stephen Hines Date: Mon, 21 Jul 2014 00:45:20 -0700 Subject: Update LLVM for rebase to r212749. Includes a cherry-pick of: r212948 - fixes a small issue with atomic calls Change-Id: Ib97bd980b59f18142a69506400911a6009d9df18 --- docs/Extensions.rst | 49 ++++++++++++++++++++++++++++++++++--------------- 1 file changed, 34 insertions(+), 15 deletions(-) (limited to 'docs/Extensions.rst') diff --git a/docs/Extensions.rst b/docs/Extensions.rst index a49485c..271c085 100644 --- a/docs/Extensions.rst +++ b/docs/Extensions.rst @@ -76,7 +76,7 @@ the target. It corresponds to the COFF relocation types Syntax: - ``.linkonce [ comdat type [ section identifier ] ]`` + ``.linkonce [ comdat type ]`` Supported COMDAT types: @@ -95,16 +95,6 @@ Supported COMDAT types: Duplicates are discarded, but the linker issues an error if any duplicates do not have exactly the same content. -``associative`` - Links the section if a certain other COMDAT section is linked. This other - section is indicated by its section identifier following the comdat type. - The following restrictions apply to the associated section: - - 1. It must be the name of a section already defined. - 2. It must differ from the current section. - 3. It must be a COMDAT section. - 4. It cannot be another associative COMDAT section. - ``largest`` Links the largest section from among the duplicates. @@ -118,10 +108,6 @@ Supported COMDAT types: .linkonce ... - .section .xdata$foo - .linkonce associative .text$foo - ... - ``.section`` Directive ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -160,6 +146,25 @@ different COMDATs: Symbol2: .long 1 +In addition to the types allowed with ``.linkonce``, ``.section`` also accepts +``associative``. The meaning is that the section is linked if a certain other +COMDAT section is linked. This other section is indicated by the comdat symbol +in this directive. It can be any symbol defined in the associated section, but +is usually the associated section's comdat. + + The following restrictions apply to the associated section: + + 1. It must be a COMDAT section. + 2. It cannot be another associative COMDAT section. + +In the following example the symobl ``sym`` is the comdat symbol of ``.foo`` +and ``.bar`` is associated to ``.foo``. + +.. code-block:: gas + + .section .foo,"bw",discard, "sym" + .section .bar,"rd",associative, "sym" + Target Specific Behaviour ========================= @@ -190,3 +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. + -- cgit v1.1