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Additional documentation for 64-bit programming

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Flesh out the documentation for 64-bit programming a little bit; in
particular, include links to the ABI documentation for various
platforms.
This commit is contained in:
H. Peter Anvin 2007-09-17 13:03:33 -07:00
parent b9957462d6
commit 2f3c4c056e
1 changed files with 55 additions and 1 deletions
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@ -6215,7 +6215,9 @@ registers, which still add their bases.
Position independence in 64-bit mode is significantly simpler, since
the processor supports \c{RIP}-relative addressing directly; see the
\c{REL} keyword (\k{effaddr}).
\c{REL} keyword (\k{effaddr}). On most 64-bit platforms, it is
probably desirable to make that the default, using the directive
\c{DEFAULT REL} (\k{default}).
64-bit programming is relatively similar to 32-bit programming, but
of course pointers are 64 bits long; additionally, all existing
@ -6223,6 +6225,58 @@ 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>}.
\H{unix64} Interfacing to 64-bit C Programs (Unix)
On Unix, the 64-bit ABI is defined by the document:
\W{http://www.x86-64.org/documentation/abi.pdf}\c{http://www.x86-64.org/documentation/abi.pdf}
Although written for AT&T-syntax assembly, the concepts apply equally
well for NASM-style assembly. What follows is a simplified summary.
The first six integer arguments (from the left) are passed in \c{RDI},
\c{RSI}, \c{RDX}, \c{RCX}, \c{R8}, and \c{R9}, in that order.
Additional integer arguments are passed on the stack. These
registers, plus \c{RAX}, \c{R10} and \c{R11} are destroyed by function
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{ST(0)} and \c{ST(1)}.
All SSE and x87 registers are destroyed by function calls.
On 64-bit Unix, \c{long} is 64 bits.
\H{win64} Interfacing to 64-bit C Programs (Win64)
The Win64 ABI is described at:
\W{http://msdn2.microsoft.com/en-gb/library/ms794533.aspx}\c{http://msdn2.microsoft.com/en-gb/library/ms794533.aspx}
What follows is a simplified summary.
The first four integer arguments are passwd in \c{RCX}, \c{RDX},
\c{R8} and \c{R9}, in that order. Additional integer arguments are
passed on the stack. These registers, plus \c{RAX}, \c{R10} and
\c{R11} are destroyed by function calls, and thus are available for
use by the function without saving.
Integer return values are passed in \c{RAX} only.
Floating point is done using SSE registers, except for \c{long
double}. Floating-point arguments are passed in \c{XMM0} to \c{XMM3};
return is \c{XMM0} only.
On Win64, \c{long} is 32 bits; \c{long long} or \c{_int64} is 64 bits.
\C{trouble} Troubleshooting