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authorNico Huber <nico.h@gmx.de>2019-02-10 20:14:57 +0100
committerNico Huber <nico.h@gmx.de>2019-02-12 22:43:21 +0000
commit540a66404591ef41e2581df01647e5788ef0c808 (patch)
treec08429942ccd65c2744e7ca89272285be36d2e07 /src
parentf751aee9268a8fe1840873ae72ed06a1cfeebf5e (diff)
cpu/x86/mtrr: Fix _FROM_4G_TOP() macro
This macro was unnecessarily complex. Trying to avoid an overflow for unknown reasons, and instead shifted the result into the sign bit in C. Using a plain number literal that forces C to use an adequate integer type seems to be safe. We start with 0xffffffff, subtract `x` and add 1 again. Turned out to be a common pattern and can't overflow for any positive 32-bit `x`. Change-Id: Ibb0c5b88a6e42d3ef2990196a5b99ace90ea8ee8 Signed-off-by: Nico Huber <nico.h@gmx.de> Reviewed-on: https://review.coreboot.org/c/31322 Tested-by: build bot (Jenkins) <no-reply@coreboot.org> Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Diffstat (limited to 'src')
-rw-r--r--src/include/cpu/x86/mtrr.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/src/include/cpu/x86/mtrr.h b/src/include/cpu/x86/mtrr.h
index eb7d78d1c5..49ed462952 100644
--- a/src/include/cpu/x86/mtrr.h
+++ b/src/include/cpu/x86/mtrr.h
@@ -150,7 +150,7 @@ static inline unsigned int fls(unsigned int x)
#define _ALIGN_DOWN_POW2(x) ((x) & ~_POW2_MASK(x))
/* Calculate `4GiB - x` (e.g. absolute address for offset from 4GiB) */
-#define _FROM_4G_TOP(x) (((1 << 20) - ((x) >> 12)) << 12)
+#define _FROM_4G_TOP(x) ((0xffffffff - (x)) + 1)
/* At the end of romstage, low RAM 0..CACHE_TM_RAMTOP may be set
* as write-back cacheable to speed up ramstage decompression.