On 10/16/19 7:17 AM, Josef Wolf wrote:
Hello all,
I experience target crashing when cross compiling for ARM with
-ftree-loop-distribute-patterns, which is enabled by the -O3 flag.
The crash happens in the startup code, before main() is called. This startup
code looks like this:
extern unsigned long _sidata; /* Set by the linker */
extern unsigned long _sdata; /* Set by the linker */
extern unsigned long _sbss; /* Set by the linker */
extern unsigned long _ebss; /* Set by the linker */
void Reet_Handler (void)
{
unsigned long *src = &_sidata
unsigned long *src = &_sdata
/* Copy data segment into RAM */
if (src != dst) {
while (dst < &_edata)
*(dst++) = *(src++);
}
/* Zero BSS segment */
dst = &_sbss;
while (dst < &_ebss)
*(dst++) = 0;
main();
}
With -ftree-loop-distribute-patterns those two loops are replaced by calls to
memcpy() and memset().
The memcpy function finishes just fine. But the memset function doesn't seem
to finish. It looks like this:
void memset (void *s, int c, size_t n)
{
int i;
for (i=0; i<n; i++)
((char *)s)[i] = c;
}
This is probably not the cause of the crash but it's worth keeping
in mind. The standard memset function returns void* and (unless
disabled) recent versions of GCC will issue a warning:
conflicting types for built-in function 'memset'; expected 'void *(void
*, int, unsigned int)' [-Wbuiltin-declaration-mismatch]
GCC expects a conforming memset and memcpy implementation even in
freestanding/embedded environments so defining these functions in
a different way could cause trouble.
Any ideas why this function is crashing? I can't see anything suspicious here.
I doubt it's the cause of the crash either but only addresses of
bytes of the same object can be used in relational expressions
(i.e., the two less-than controlling expressions). Using address
to unrelated objects is undefined. Concerns about invalidating
code like the above prevents compilers from implementing useful
optimizations.
GCC doesn't issue a warning for this bug yet but it might in
the future. To avoid the undefined behavior and future
warnings, convert the addresses to uintptr_t first and compare
those instead.
Martin
