[x86 setup] Correct the SMAP check for INT 0x15, AX=0xe820 (4ee5b10a) · Commits · 戴 / test

The e820 probe code was checking %edx, not %eax, for the SMAP signature on return. This worked on *almost* all systems, since %edx still contained SMAP from the call on entry, but on a handful of systems it failed -- plus, we would have missed real mismatches. The error output is "=d" to make sure gcc knows %edx is clobbered here. Signed-off-by:

H. Peter Anvin <hpa@zytor.com>

arch/i386/boot/memory.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -28,11 +28,14 @@ static int detect_memory_e820(void)

		do {
		size = sizeof(struct e820entry);
		id = SMAP;

		/* Important: %edx is clobbered by some BIOSes,
		so it must be either used for the error output
		or explicitly marked clobbered. */
		asm("int $0x15; setc %0"
		: "=am" (err), "+b" (next), "+d" (id), "+c" (size),
		: "=d" (err), "+b" (next), "=a" (id), "+c" (size),
		"=m" (*desc)
		: "D" (desc), "a" (0xe820));
		: "D" (desc), "d" (SMAP), "a" (0xe820));

		/* Some BIOSes stop returning SMAP in the middle of
		the search loop. We don't know exactly how the BIOS

Admin message