Post by Sam Habiel Post by Corinna Vinschen Post by Sam Habiel Post by Yaakov Selkowitz Post by Sam Habiel
GT.M contains a large
amount of assembly code, written to run on the x32 Linux ABI and the
AMD x64 ABI. It's was very easy to get the x32 Linux ABI to run on
Cygwin x32; Cygwin x64 on the other hand uses the Windows x64 ABI,
I don't have the expertise nor the time to rewrite a lot of assembly
code to use the Windows x64 ABI. There are about 100 source code files
that are in assembly.
Are you telling me that gcc has a flag to support AMD ABI on Cygwin
x64? The assembly code is not standalone; it gets called from C code
and calls C code.
That's what he's telling you. However, you have to interact with the MS
ABI(*) as well as soon as you call external library functions so it
makes sense to keep your C code in MS ABI. For the assembler functions,
you can just tell the compiler they are in SYSV ABI by adding a function
int asm_func (args) __attribute__ ((sysv_abi))
This sounds very promising, but I would like a clarification; because
1. There are frequent calls from the C code to Assembly.
2. There are also frequent calls from Assembly to C code.
Looks like compiling the .s files with the -mabi=sysv flag and
declaring the function in C with the __attribute__ ((sysv_abi)) will
You shouldn't have to use the flag when building the assembler files,
they are using SYSV ABI anyway. In fact, while Yaakov is right,
basically, I think in your scenario you should only use the GCC function
attribute since that allows more fine-grained control. Just stick to MS
ABI by default and only perform the SYSV ABI juggle where required to
interact with the assembler code.
Post by Sam Habiel
How about #2? I don't see an easy solution. The assembly code puts
together the parameters in the registers in the sysv way (rdi, rsi,
rdx, rcx, r8, r9), not rcx, rdx, r8, and r9.
One way is to create a SYSV wrapper for each C function called from
assembler. Assuming this simple scenario:
There's a C function foo(), which is called from assembler as
well as from other C functions.
extern long foo (long, double, int, long);
For the "normal" (i.e. MS ABI) C code add this in front of the above
#define foo(a,b,c,d) __foo((a),(b),(c),(d))
So the C function is renamed to __foo and C code will call __foo.
Add a wrapper C file to add a function foo with SYSV ABI, calling
long __attribute__ ((sysv_abi))
foo (long a, double b, int c, long d)
return __foo (a,b,c,d);
That should do it. Of course there may be more complicated cases,
but I leave them as excercise for the reader, and only you are in
a position to know them ;)