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Fix miscompile with dead switches

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In certain very specific situations (involving switches
with asms inside dead statement expressions) we could generate
invalid code (clobbering the buffer so much that we generated
invalid instructions).  Don't emit the decision table if the
switch itself is dead.
This commit is contained in:
Michael Matz
2016-10-18 03:31:14 +02:00
parent 7ae35bf1bb
commit d042e71e9f
2 changed files with 60 additions and 7 deletions
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51
tests/tcctest.c
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@ -2964,6 +2964,56 @@ void test_high_clobbers(void)
asm volatile("mov %%r12, %0" : "=r" (val2) : "r" (val): "memory");
printf("asmhc: 0x%x\n", val2);
#endif
}
static long cpu_number;
void trace_console(long len, long len2)
{
/* This generated invalid code when the emission of the switch
table isn't disabled. The asms are necessary to show the bug,
normal statements don't work (they need to generate some code
even under nocode_wanted, which normal statements don't do,
but asms do). Also at least these number of cases is necessary
to generate enough "random" bytes. They ultimately are enough
to create invalid instruction patterns to which the first
skip-to-decision-table jump jumps. If decision table emission
is disabled all of this is no problem.
It also is necessary that the switches are in a statement expression
(which has the property of not being enterable from outside. no
matter what). */
if (0
&&
({
long pscr_ret__;
switch(len) {
case 4:
{
long pfo_ret__;
switch (len2) {
case 8: printf("bla"); pfo_ret__ = 42; break;
}
pscr_ret__ = pfo_ret__;
}
break;
case 8:
{
long pfo_ret__;
switch (len2) {
case 1:asm("movq %1,%0": "=r" (pfo_ret__) : "m" (cpu_number)); break;
case 2:asm("movq %1,%0": "=r" (pfo_ret__) : "m" (cpu_number)); break;
case 4:asm("movq %1,%0": "=r" (pfo_ret__) : "m" (cpu_number)); break;
case 8:asm("movq %1,%0": "=r" (pfo_ret__) : "m" (cpu_number)); break;
default: printf("impossible\n");
}
pscr_ret__ = pfo_ret__;
};
break;
}
pscr_ret__;
}))
{
printf("huh?\n");
}
}
void asm_test(void)
@ -3044,6 +3094,7 @@ void asm_test(void)
fancy_copy2 (&val, &val2);
printf ("fancycpy2(%d)=%d\n", val, val2);
asm volatile ("mov $0x4243, %%esi" : "=r" (regvar));
printf ("regvar=%x\n", regvar);
test_high_clobbers();
trace_console(8, 8);
return;