Author: Armin Rigo <ar...@tunes.org>
Branch:
Changeset: r65597:b924d55fe87a
Date: 2013-07-24 12:01 +0200
http://bitbucket.org/pypy/pypy/changeset/b924d55fe87a/
Log: Add comments
diff --git a/rpython/jit/backend/x86/assembler.py
b/rpython/jit/backend/x86/assembler.py
--- a/rpython/jit/backend/x86/assembler.py
+++ b/rpython/jit/backend/x86/assembler.py
@@ -735,6 +735,10 @@
self.mc.RET()
def _load_shadowstack_top_in_ebx(self, mc, gcrootmap):
+ """Loads the shadowstack top in ebx, and returns an integer
+ that gives the address of the stack top. If this integer doesn't
+ fit in 32 bits, it will be loaded in r11.
+ """
rst = gcrootmap.get_root_stack_top_addr()
if rx86.fits_in_32bits(rst):
mc.MOV_rj(ebx.value, rst) # MOV ebx, [rootstacktop]
@@ -752,6 +756,9 @@
if rx86.fits_in_32bits(rst):
self.mc.MOV_jr(rst, ebx.value) # MOV [rootstacktop], ebx
else:
+ # The integer 'rst' doesn't fit in 32 bits, so we know that
+ # _load_shadowstack_top_in_ebx() above loaded it in r11.
+ # Reuse it. Be careful not to overwrite r11 in the middle!
self.mc.MOV_mr((X86_64_SCRATCH_REG.value, 0),
ebx.value) # MOV [r11], ebx
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