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Date: Tue, 18 Apr 2006 05:32:00 -0000
Subject: [Bug c/27192]  New: call through function pointer goes to wrong address
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From: "regehr at cs dot utah dot edu" <gcc-bugzilla@gcc.gnu.org>
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The program below confuses gcc in such a way that it generates code loading the
byte-address of bar() into the Z register, which causes icall to jump off to
neverneverland.  Rather, the double-byte address of bar() should be loaded into
Z before the indirect call.

This bug is also present in gcc 4.0.3 and 3.4.3.

avr-gcc -v gives:

Target: avr
Configured with: ../gcc-4.1.0/configure --prefix=/home/regehr/gcc-4.1.0-avr-bin
--disable-libssp --disable-nls --target=avr
Thread model: single
gcc version 4.1.0

Compile with:

  avr-gcc -Os -Wall shifty.c -o shifty.elf

Program:

struct fseqp_void
{
    void (*p) (void);
    char *e;
};

struct fseqp_void c[2];

void bar (void)
{
}

void foo (void)
{
    int i;
    for (i=0; i<32; i++);
}

int main (void)
{
    c[0].e = (char *)bar + 2;
    c[0].p = bar;
    foo ();
    struct fseqp_void x = c[0];
    void (*start) (void) = x.p;
    (*start)();
    return 0;
}


-- 
           Summary: call through function pointer goes to wrong address
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: regehr at cs dot utah dot edu
  GCC host triplet: i686-linux-gnu
GCC target triplet: avr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27192