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Re: [avr-gcc-list] avr-gcc 3.4.3 confused about function pointers

From: John Regehr
Subject: Re: [avr-gcc-list] avr-gcc 3.4.3 confused about function pointers
Date: Mon, 17 Apr 2006 20:55:48 -0600
User-agent: Thunderbird 1.5 (X11/20060111)

> Sorry, I can't follow the somewhat tangled logic of that code, so I
> can't see whether GCC 4.1.0 still produces buggy code for it or not.

You weren't supposed to follow the logic, it was an automatically
extracted subset of a machine generated file.

A shorter program that gcc 4.1.0 miscompiles is below.  Compile with -Os
and the problem should be obvious: the program icalls to the byte
address of bar() rather than the double-byte address.

John Regehr

struct fseqp_void
  void (*p) (void);
  void (*e) (void);

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 = bar + 1;
  c[0].p = bar;
  foo ();
  struct fseqp_void x = c[0];
  void (*start) (void) = x.p;
  ((*start)) ();
  return 0;

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