GLIBC bug with float and swapcontext

glibc_swapcontext_float.c

/* build with gcc -g -Os -m32 testfp.c */

#include <stdio.h>
#include <stdlib.h>
#include <ucontext.h>
#include <signal.h>
#include <assert.h>

ucontext_t context_step0;
ucontext_t context_step1;
ucontext_t context_step2;

void step1(void)
{
   volatile register float x1 = 0.123;
   volatile register float x2 = 0.234;
   register float y1;
   register float y2;

   y1 = x1 * x2;
   swapcontext (&context_step1, &context_step2);
   y2 = x1 * x2;
   assert (y1 == y2);
   swapcontext (&context_step1, &context_step2);
}

void step2(void)
{
   volatile register float x1 = 0.425;
   volatile register float x2 = 0.455;
   register float y1;
   register float y2;

   y1 = x1 * x2;
   swapcontext (&context_step2, &context_step1);
   y2 = x1 * x2;
   assert (y1 == y2);
   swapcontext (&context_step2, &context_step0);
}


int main(void)
{
    char step1_stack[SIGSTKSZ];
    char step2_stack[SIGSTKSZ];

    getcontext(&context_step1);
    context_step1.uc_link          = &context_step0;
    context_step1.uc_stack.ss_sp   = step1_stack;
    context_step1.uc_stack.ss_size = sizeof(step1_stack);
    makecontext(&context_step1, (void (*)(void)) step1, 0);


    getcontext(&context_step2);
    context_step2.uc_link          = &context_step0;
    context_step2.uc_stack.ss_sp   = step2_stack;
    context_step2.uc_stack.ss_size = sizeof(step2_stack);
    makecontext(&context_step2, (void (*)(void)) step2, 0);

    /* start step 1*/
    swapcontext (&context_step0, &context_step1);

    return 0;
}