Re:  problem while building arm vfp softfloat gcc

[Richard Earnshaw <rearnsha at arm dot com>]

> > sorry for my testcase, I had rewriten it to easy to understand, but on the
> > contrary...
> > Here is my true test case using printf:
> > ----main.c
> > #include <stdio.h>
> > #include <stdlib.h>
> > 
> > int main()
> > {
> >         float i=1.0;
> >         printf("%f",i);
> >         return 0;
> > }
> > ----main.c
> > 
> > here is generated by arm-linux-gcc -S main.c -o main.s
> > ----main.s
> > <sniz>
> > main:
> >           @ args = 0, pretend = 0, frame = 4
> >           @ frame_needed = 1, uses_anonymous_args = 0
> >           mov     ip, sp
> >           stmfd   sp!, {r4, fp, ip, lr, pc}
> >           sub     fp, ip, #4
> >           sub     sp, sp, #4
> >           ldr     r3, .L2 @ float
> >           str     r3, [fp, #-20]  @ float
> >           ldr     r0, [fp, #-20]  @ float
> >           bl      __extendsfdf2
> >           mov     r4, r1
> >           mov     r3, r0
> >           ldr     r0, .L2+4
> >           mov     r2, r4
> >           mov     r1, r3
> >           bl      printf
> >           mov     r3, #0
> >           mov     r0, r3
> > <sniz>
> > -----main.s
> > 
> > if I arm-linux-gcc main.s -o test
> > then execute test on pxa board, it will output: -1.999744
> > 
> > but if I modified the two lines before "bl printf" in main.s to:
> > mov	r2, r3
> > mov	r3, r4
> > then compile main.s and execute,
> > it will print right result: 1.00000
> > 
> > so conclusion:
> > my toolchain must has a problem of float param passing, seemly related to
> > float word order. so I want to dig into my gcc source tree to find where is
> > responsible for generating this wrong asm code.
> > I hope this time it's clearer :)
> > 
> > and Dan, I think the most recently snapshot ptxdist still has this problem
> > :(
> 
> The code above is correct.  You should not be doing a word order swap 
> before the call to printf.
> 
> So I think the problem must be in your printf library function (or a 
> subroutine of that).  Two possibilities here:
> 
> 1) The library was compiled without soft-vfp (it for traditional FPA 
> format floats).
> 2) The library needs porting to support soft-vfp (there will probably be 
> #ifdef __arm__ somewhere in the library, where the code will then assume 
> that you have FPA format floats).
> 

There is of course, one more possibility.  Do you get correct output if 
you compile the following program?

#include <stdio.h>
#include <stdlib.h>

int main()
{
        double i=1.0;
        printf("%f",i);
        return 0;
}

If you do, then the problem is most likely in the call to __extendsfdf2

R.


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