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.venv/Lib/site-packages/greenlet/platform/switch_aarch64_gcc.h

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+/*
+ * this is the internal transfer function.
+ *
+ * HISTORY
+ * 07-Sep-16 Add clang support using x register naming. Fredrik Fornwall
+ * 13-Apr-13 Add support for strange GCC caller-save decisions
+ * 08-Apr-13 File creation. Michael Matz
+ *
+ * NOTES
+ *
+ * Simply save all callee saved registers
+ *
+ */
+
+#define STACK_REFPLUS 1
+
+#ifdef SLP_EVAL
+#define STACK_MAGIC 0
+#define REGS_TO_SAVE "x19", "x20", "x21", "x22", "x23", "x24", "x25", "x26", \
+                     "x27", "x28", "x30" /* aka lr */, \
+                     "v8", "v9", "v10", "v11", \
+                     "v12", "v13", "v14", "v15"
+
+/*
+ * Recall:
+   asm asm-qualifiers ( AssemblerTemplate
+                 : OutputOperands
+                 [ : InputOperands
+                 [ : Clobbers ] ])
+
+ or  (if asm-qualifiers contains 'goto')
+
+   asm asm-qualifiers ( AssemblerTemplate
+                      : OutputOperands
+                      : InputOperands
+                      : Clobbers
+                      : GotoLabels)
+
+ and OutputOperands are
+
+   [ [asmSymbolicName] ] constraint (cvariablename)
+
+ When a name is given, refer to it as ``%[the name]``.
+ When not given, ``%i`` where ``i`` is the zero-based index.
+
+ constraints starting with ``=`` means only writing; ``+`` means
+ reading and writing.
+
+ This is followed by ``r`` (must be register) or ``m`` (must be memory)
+ and these can be combined.
+
+ The ``cvariablename`` is actually an lvalue expression.
+
+ In AArch65, 31 general purpose registers. If named X0... they are
+ 64-bit. If named W0... they are the bottom 32 bits of the
+ corresponding 64 bit register.
+
+ XZR and WZR are hardcoded to 0, and ignore writes.
+
+ Arguments are in X0..X7. C++ uses X0 for ``this``. X0 holds simple return
+ values (?)
+
+ Whenever a W register is written, the top half of the X register is zeroed.
+ */
+
+static int
+slp_switch(void)
+{
+	int err;
+	void *fp;
+        /* Windowz uses a 32-bit long on a 64-bit platform, unlike the rest of
+           the world, and in theory we can be compiled with GCC/llvm on 64-bit
+           windows. So we need a fixed-width type.
+        */
+        int64_t *stackref, stsizediff;
+        __asm__ volatile ("" : : : REGS_TO_SAVE);
+	__asm__ volatile ("str x29, %0" : "=m"(fp) : : );
+        __asm__ ("mov %0, sp" : "=r" (stackref));
+        {
+                SLP_SAVE_STATE(stackref, stsizediff);
+                __asm__ volatile (
+                    "add sp,sp,%0\n"
+                    "add x29,x29,%0\n"
+                    :
+                    : "r" (stsizediff)
+                    );
+		SLP_RESTORE_STATE();
+		/* SLP_SAVE_STATE macro contains some return statements
+		   (of -1 and 1).  It falls through only when
+		   the return value of slp_save_state() is zero, which
+		   is placed in x0.
+		   In that case we (slp_switch) also want to return zero
+		   (also in x0 of course).
+		   Now, some GCC versions (seen with 4.8) think it's a
+		   good idea to save/restore x0 around the call to
+		   slp_restore_state(), instead of simply zeroing it
+		   at the return below.  But slp_restore_state
+		   writes random values to the stack slot used for this
+		   save/restore (from when it once was saved above in
+		   SLP_SAVE_STATE, when it was still uninitialized), so
+		   "restoring" that precious zero actually makes us
+		   return random values.  There are some ways to make
+		   GCC not use that zero value in the normal return path
+		   (e.g. making err volatile, but that costs a little
+		   stack space), and the simplest is to call a function
+		   that returns an unknown value (which happens to be zero),
+		   so the saved/restored value is unused.
+
+                   Thus, this line stores a 0 into the ``err`` variable
+                   (which must be held in a register for this instruction,
+                    of course). The ``w`` qualifier causes the instruction
+                    to use W0 instead of X0, otherwise we get a warning
+                    about a value size mismatch (because err is an int,
+                    and aarch64 platforms are LP64: 32-bit int, 64 bit long
+                   and pointer).
+                */
+           __asm__ volatile ("mov %w0, #0" : "=r" (err));
+        }
+        __asm__ volatile ("ldr x29, %0" : : "m" (fp) :);
+        __asm__ volatile ("" : : : REGS_TO_SAVE);
+        return err;
+}
+
+#endif