Hello,
The cyg_io_init call in packages/common/io/v3_0/src/iosys.c depends on
undefined compiler behavior and break in practice. There are problems start
here:
void
cyg_io_init(void)
{
static int _init = false;
cyg_devtab_entry_t *t;
if (_init) return;
for (t = &__DEVTAB__[0]; t != &__DEVTAB_END__; t++) {
The trouble is in the "t != &__DEVTAB_END__" check.
First problem:
The compiler is certainly allowed to assume that two different identifiers
cannot have the same address. C guarantees this. So, the output binary does
not need to check the t != condition on first entry into the loop. In other
words, the loop can *always* iterate at least once, despite the intent of the
"t!=" check. We found this the hard way by entering the loop with an empty
table and faulting on a null.
Second problem:
Writing code that depends on relative location of two different identifiers in
the data segment is dodgy. This code specifically assumes that 't' will roll
off the array and immediately point to __DEVTAB_END__. Some serious linker
sorcery to guarantee that, and this approach requires that the table have at
least one entry, which is not always going to happen.
I hope this is useful.
Regards,
-steve
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