[commit: ghc] wip/T16106: Rewrite comment on C calling convention (0bf5d91)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : wip/T16106
Link       : http://ghc.haskell.org/trac/ghc/changeset/0bf5d91e322293ed3e509ba96bf49140d418c4a8/ghc

>---------------------------------------------------------------

commit 0bf5d91e322293ed3e509ba96bf49140d418c4a8
Author: Peter Trommler <ptrommler at acm.org>
Date:   Mon Dec 31 16:46:22 2018 +0100

    Rewrite comment on C calling convention


>---------------------------------------------------------------

0bf5d91e322293ed3e509ba96bf49140d418c4a8
 compiler/nativeGen/PPC/CodeGen.hs | 45 ++++++++++++++++++++-------------------
 1 file changed, 23 insertions(+), 22 deletions(-)

diff --git a/compiler/nativeGen/PPC/CodeGen.hs b/compiler/nativeGen/PPC/CodeGen.hs
index a69bd9c..bbc3411 100644
--- a/compiler/nativeGen/PPC/CodeGen.hs
+++ b/compiler/nativeGen/PPC/CodeGen.hs
@@ -1587,48 +1587,49 @@ genCCall'
     -> [CmmActual]        -- arguments (of mixed type)
     -> NatM InstrBlock
 
-{- TODO: Remove references to Darwin and rewrite to integrate 64-bit ABIs
-         and AIX.
+{- 
     PowerPC Linux uses the System V Release 4 Calling Convention
     for PowerPC. It is described in the
     "System V Application Binary Interface PowerPC Processor Supplement".
 
-    Both conventions are similar:
+    PowerPC 64 Linux uses the System V Release 4 Calling Convention for
+    64-bit PowerPC. It is specified in
+    "64-bit PowerPC ELF Application Binary Interface Supplement 1.9"
+    (PPC64 ELF v1.9).
+
+    PowerPC 64 Linux in little endian mode uses the "Power Architecture 64-Bit
+    ELF V2 ABI Specification -- OpenPOWER ABI for Linux Supplement"
+    (PPC64 ELF v2).
+
+    AIX follows the "PowerOpen ABI: Application Binary Interface Big-Endian
+    32-Bit Hardware Implementation"
+
+    All four conventions are similar:
     Parameters may be passed in general-purpose registers starting at r3, in
     floating point registers starting at f1, or on the stack.
 
     But there are substantial differences:
     * The number of registers used for parameter passing and the exact set of
       nonvolatile registers differs (see MachRegs.hs).
-    * On Darwin, stack space is always reserved for parameters, even if they are
-      passed in registers. The called routine may choose to save parameters from
-      registers to the corresponding space on the stack.
-    * On Darwin, a corresponding amount of GPRs is skipped when a floating point
-      parameter is passed in an FPR.
+    * On AIX and 64-bit ELF, stack space is always reserved for parameters,
+      even if they are passed in registers. The called routine may choose to
+      save parameters from registers to the corresponding space on the stack.
+    * On AIX and 64-bit ELF, a corresponding amount of GPRs is skipped when
+      a floating point parameter is passed in an FPR.
     * SysV insists on either passing I64 arguments on the stack, or in two GPRs,
       starting with an odd-numbered GPR. It may skip a GPR to achieve this.
-      Darwin just treats an I64 like two separate II32s (high word first).
+      AIX just treats an I64 likt two separate I32s (high word first).
     * I64 and FF64 arguments are 8-byte aligned on the stack for SysV, but only
-      4-byte aligned like everything else on Darwin.
+      4-byte aligned like everything else on AIX.
     * The SysV spec claims that FF32 is represented as FF64 on the stack. GCC on
       PowerPC Linux does not agree, so neither do we.
 
-    PowerPC 64 Linux uses the System V Release 4 Calling Convention for
-    64-bit PowerPC. It is specified in
-    "64-bit PowerPC ELF Application Binary Interface Supplement 1.9"
-    (PPC64 ELF v1.9).
-    PowerPC 64 Linux in little endian mode uses the "Power Architecture 64-Bit
-    ELF V2 ABI Specification -- OpenPOWER ABI for Linux Supplement"
-    (PPC64 ELF v2).
-    AIX follows the "PowerOpen ABI: Application Binary Interface Big-Endian
-    32-Bit Hardware Implementation"
-
     According to all conventions, the parameter area should be part of the
     caller's stack frame, allocated in the caller's prologue code (large enough
     to hold the parameter lists for all called routines). The NCG already
     uses the stack for register spilling, leaving 64 bytes free at the top.
-    If we need a larger parameter area than that, we just allocate a new stack
-    frame just before ccalling.
+    If we need a larger parameter area than that, we increase the size
+    of the stack frame just before ccalling.
 -}