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Date: Wed, 23 Jan 2008 20:58:00 -0000
Subject: [Bug c/34947]  New: Clobbered float registers not popped
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From: "vincent dot riviere at freesbee dot fr" <gcc-bugzilla@gcc.gnu.org>
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This problem is about functions that push some float registers at the
beginning, but forget to pop them at the end. The stack pointer is not adjusted
as expected, so the function return to an invalid address.

It appears when the following is true:
- the file is compiled with -m68020-60 -O1 -fomit-frame-pointer
- the function uses floats
- the function is complicated enough to have some float registers backed up on
the stack
- there is an early return in the function

The problem appears in the following test case:
$ cat bug.c
volatile float g1;
float g2;

void f(void)
{
    float i;

    if (g2 >= 0)
        return;

    for (i = 0; i < 10; ++i)
        g1 = g2 + i;
}

$ gcc -S bug.c -o - -m68020-60 -O2 -fomit-frame-pointer
...
        .globl  f
        .type   f, @function
f:
        fmovm #0x4,-(%sp)
        fmove.s g2,%fp2
        fbnge .L9
.L5:
        rts
.L9:
...

We can see that some float registers are backuped at the beginning. Then (g2 >=
0) is checked. If it is the case, the function returns with a simple rts,
without restoring the registers, to an invalid address.

This happens in gcc 4.2.2 and gcc-4.2-20080116


-- 
           Summary: Clobbered float registers not popped
           Product: gcc
           Version: 4.2.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: vincent dot riviere at freesbee dot fr
GCC target triplet: m68k-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34947