Registers to protect
lazarus / 1-Linux

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sean_vn · 2014-07-19 05:30

I have written some assembly language code in FP for x64 Linux.  I
couldn't find the exact calling conventions.  I presumed the standard
AMD64 Linux conventions, the same as C on that platform.
It seemed to work at first for simple test programs but now things are
getting messed up when I try larger programs.
What is the exact calling convention and what registers must be
protected. 

I assume parameters are passed as rdi,rsi,rdx,r8,r9,r10,r11
I assume a function result is returned in rax.
I assume I can anyway trash rax,rcx,rdx,r8,r9,r10,r11
I assume I must preserve  rbp,rbx,r12,r13,r14,r15 across a function or
procedure call but can use them inside a function or procedure. 
Perhaps I'm goofing up because I am using class types.  Perhaps the
reference to self (this) is in a register and I need to protect it?

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Leledumbo · 2014-07-19 08:46

AFAIK there's only 1 ABI for x86_64-linux, I'm not sure though about
register use and order in parameters, but as been documented here, you
can tell the compiler which registers to preserve.

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sean_vn · 2014-07-19 15:06

I thought I was getting illegal memory access exceptions.  I think
what is happening is that numerical overflows involving floating point
usage of the SSE registers are throwing an exception/interrupt rather
than giving the expected NaN result.  I have to go and set something
in a control register do I?  Me go look.

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sean_vn · 2014-07-19 16:05

implementation
var
modeData:LongWord=$9fc0; 
{$ASMMODE Intel} 
procedure setmode();assembler;
asm
  ldmxcsr modeData
end;

Mask all SSE F.P exceptions, flush to zero, denormals are zero

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Leledumbo · 2014-07-19 17:31

Quote from: sean_vn on July 19, 2014, 06:05:17 pmimplementation
var
modeData:LongWord=$9fc0; 
{$ASMMODE Intel} 
procedure setmode();assembler;
asm
  ldmxcsr modeData
end;

Mask all SSE F.P exceptions, flush to zero, denormals are zero
Or the Pascal level API: http://www.freepascal.org/docs-
html/rtl/math/setexceptionmask.html