Diffusion FreeBSD src repository 35a1aa5f9c20

[PowerPC] Fix outdated FP regs on fork(2) and friends
35a1aa5f9c20
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Description

[PowerPC] Fix outdated FP regs on fork(2) and friends

Summary:
Failure to update the FP / vector state was causing daemon(3) to violate C ABI by failing to preserve nonvolatile registers.

This was causing a weird issue where moused was not working on PowerBook G4s when daemonizing, but was working fine when running it foreground.

Force saving off the same state that cpu_switch() does in cases where we are about to copy a thread.

MFC after: 1 week
Sponsored by: Tag1 Consulting, Inc.

Test Plan:

/*
 * Test for ABI violation due to side effects of daemon(3).
 *
 * NOTE: Compile with -O2 to see the effect.
 */
/* Allow compiling for Linux too. */

static double test = 1234.56f;

/*
 * This contrivance coerces clang to not bounce the double
 * off of memory again in main.
 */
void __attribute__((noinline))
print_double(int j1, int j2, double d)
{
	printf("%f\n", d);
}

int
main(int argc, char *argv[])
{
	print_double(0, 0, test);

	if (daemon(0, 1)) {
	}
	/* Compiler assumes nonvolatile regs are intact... */
	print_double(0, 0, test);
	return(0);
}

Working output: