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authorH. Peter Anvin <hpa@linux.intel.com>2018-02-07 12:28:42 -0800
committerH. Peter Anvin <hpa@linux.intel.com>2018-02-07 12:28:42 -0800
commitcb7b097b3e7968c59c528474d2a2ede0ae28dad0 (patch)
tree3e52163e30ad2d5748e5439a1e4b708efaaa2e41 /doc/nasmdoc.src
parentddea5fc0cdbef204a7713ad2fd856484df71308d (diff)
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doc: some more documentation on 64-bit programming
Some more information about 64-bit programming and its quirks. Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'doc/nasmdoc.src')
-rw-r--r--doc/nasmdoc.src21
1 files changed, 14 insertions, 7 deletions
diff --git a/doc/nasmdoc.src b/doc/nasmdoc.src
index 2f6c533f..7b331d35 100644
--- a/doc/nasmdoc.src
+++ b/doc/nasmdoc.src
@@ -7704,10 +7704,15 @@ platforms pass arguments in registers rather than on the stack.
Furthermore, 64-bit platforms use SSE2 by default for floating point.
Please see the ABI documentation for your platform.
-64-bit platforms differ in the sizes of the fundamental datatypes, not
-just from 32-bit platforms but from each other. If a specific size
-data type is desired, it is probably best to use the types defined in
-the Standard C header \c{<inttypes.h>}.
+64-bit platforms differ in the sizes of the C/C++ fundamental
+datatypes, not just from 32-bit platforms but from each other. If a
+specific size data type is desired, it is probably best to use the
+types defined in the standard C header \c{<inttypes.h>}.
+
+All known 64-bit platforms except some embedded platforms require that
+the stack is 16-byte aligned at the entry to a function. In order to
+enforce that, the stack pointer (\c{RSP}) needs to be aligned on an
+\c{odd} multiple of 8 bytes before the \c{CALL} instruction.
In 64-bit mode, the default instruction size is still 32 bits. When
loading a value into a 32-bit register (but not an 8- or 16-bit
@@ -7815,9 +7820,11 @@ calls, and thus are available for use by the function without saving.
Integer return values are passed in \c{RAX} and \c{RDX}, in that order.
Floating point is done using SSE registers, except for \c{long
-double}. Floating-point arguments are passed in \c{XMM0} to \c{XMM7};
-return is \c{XMM0} and \c{XMM1}. \c{long double} are passed on the
-stack, and returned in \c{ST0} and \c{ST1}.
+double}, which is 80 bits (\c{TWORD}) on most platforms (Android is
+one exception; there \c{long double} is 64 bits and treated the same
+as \c{double}.) Floating-point arguments are passed in \c{XMM0} to
+\c{XMM7}; return is \c{XMM0} and \c{XMM1}. \c{long double} are passed
+on the stack, and returned in \c{ST0} and \c{ST1}.
All SSE and x87 registers are destroyed by function calls.