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fortify: Use C arithmetic not FIELD_xxx() in FORTIFY_REASON defines

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FIELD_GET() and FIELD_PREP() are mainly useful for hardware register
accesses, but here they are being used for some very simple oprations.

This wouldn't matter much, but they contain a lot of compile-time
checks (that really aren't needed here) that bloat the expansion
of FIELD_GET(GENMASK(7, 1), func) to over 18KB.
Even with the 'bloat reduced' FIELD_GET/PREP they are still hundreds of
characters.

Replace FIELD_GET(BIT(0), r) with ((r) & 1), FIELD_GET(GENMASK(7, 1), r) with
(r) >> 1), and (FIELD_PREP(BIT(0), write) | FIELD_PREP(GENMASK(7, 1), func))
with ((func) << 1 | (write)).

The generated code is the same, but it makes the .c file less obfuctaced,
the .i file much easier to read, and should marginally decrease compilation
time.

Signed-off-by: David Laight <david.laight.linux@gmail.com>
Link: https://patch.msgid.link/20251214125857.3308-1-david.laight.linux@gmail.com
Signed-off-by: Kees Cook <kees@kernel.org>
This commit is contained in:
David Laight
2025-12-14 12:58:57 +00:00
committed by Kees Cook
parent cc34c669ab
commit 995ddc58d7
1 changed files with 3 additions and 5 deletions
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8
include/linux/fortify-string.h
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@@ -2,7 +2,6 @@
#ifndef _LINUX_FORTIFY_STRING_H_
#define _LINUX_FORTIFY_STRING_H_
#include <linux/bitfield.h>
#include <linux/bug.h>
#include <linux/const.h>
#include <linux/limits.h>
@@ -10,10 +9,9 @@
#define __FORTIFY_INLINE extern __always_inline __gnu_inline __overloadable
#define __RENAME(x) __asm__(#x)
#define FORTIFY_REASON_DIR(r) FIELD_GET(BIT(0), r)
#define FORTIFY_REASON_FUNC(r) FIELD_GET(GENMASK(7, 1), r)
#define FORTIFY_REASON(func, write) (FIELD_PREP(BIT(0), write) | \
FIELD_PREP(GENMASK(7, 1), func))
#define FORTIFY_REASON_DIR(r) ((r) & 1)
#define FORTIFY_REASON_FUNC(r) ((r) >> 1)
#define FORTIFY_REASON(func, write) ((func) << 1 | (write))
/* Overridden by KUnit tests. */
#ifndef fortify_panic