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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Peter Jones <pjones@redhat.com>
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Date: Mon, 21 Mar 2022 16:06:10 -0400
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Subject: [PATCH] misc: Make grub_min() and grub_max() more resilient.
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grub_min(a,b) and grub_max(a,b) use a relatively naive implementation
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which leads to several problems:
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- they evaluate their parameters more than once
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- the naive way to address this, to declare temporary variables in a
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statement-expression, isn't resilient against nested uses, because
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MIN(a,MIN(b,c)) results in the temporary variables being declared in
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two nested scopes, which may result in a build warning depending on
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your build options.
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This patch changes our implementation to use a statement-expression
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inside a helper macro, and creates the symbols for the temporary
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variables with __COUNTER__ (A GNU C cpp extension) and token pasting to
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create uniquely named internal variables.
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Signed-off-by: Peter Jones <pjones@redhat.com>
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---
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grub-core/loader/multiboot_elfxx.c | 4 +---
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include/grub/misc.h | 25 +++++++++++++++++++++++--
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2 files changed, 24 insertions(+), 5 deletions(-)
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diff --git a/grub-core/loader/multiboot_elfxx.c b/grub-core/loader/multiboot_elfxx.c
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index f2318e0d16..87f6e31aa6 100644
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--- a/grub-core/loader/multiboot_elfxx.c
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+++ b/grub-core/loader/multiboot_elfxx.c
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@@ -35,9 +35,7 @@
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#endif
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#include <grub/i386/relocator.h>
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-
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-#define CONCAT(a,b) CONCAT_(a, b)
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-#define CONCAT_(a,b) a ## b
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+#include <grub/misc.h>
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#pragma GCC diagnostic ignored "-Wcast-align"
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diff --git a/include/grub/misc.h b/include/grub/misc.h
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index 6c4aa85ac5..cf84aec1db 100644
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--- a/include/grub/misc.h
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+++ b/include/grub/misc.h
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@@ -35,6 +35,14 @@
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#define ARRAY_SIZE(array) (sizeof (array) / sizeof (array[0]))
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#define COMPILE_TIME_ASSERT(cond) switch (0) { case 1: case !(cond): ; }
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+#ifndef CONCAT_
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+#define CONCAT_(a, b) a ## b
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+#endif
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+
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+#ifndef CONCAT
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+#define CONCAT(a, b) CONCAT_(a, b)
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+#endif
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+
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#define grub_dprintf(condition, ...) grub_real_dprintf(GRUB_FILE, __LINE__, condition, __VA_ARGS__)
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void *EXPORT_FUNC(grub_memmove) (void *dest, const void *src, grub_size_t n);
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@@ -498,8 +506,21 @@ void EXPORT_FUNC(grub_real_boot_time) (const char *file,
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#define grub_boot_time(...)
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#endif
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-#define grub_max(a, b) (((a) > (b)) ? (a) : (b))
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-#define grub_min(a, b) (((a) < (b)) ? (a) : (b))
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+#define _grub_min(a, b, _a, _b) \
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+ ({ typeof (a) _a = (a); \
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+ typeof (b) _b = (b); \
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+ _a < _b ? _a : _b; })
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+#define grub_min(a, b) _grub_min(a, b, \
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+ CONCAT(_a_,__COUNTER__), \
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+ CONCAT(_b_,__COUNTER__))
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+
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+#define _grub_max(a, b, _a, _b) \
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+ ({ typeof (a) _a = (a); \
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+ typeof (b) _b = (b); \
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+ _a > _b ? _a : _b; })
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+#define grub_max(a, b) _grub_max(a, b, \
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+ CONCAT(_a_,__COUNTER__), \
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+ CONCAT(_b_,__COUNTER__))
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#define grub_log2ull(n) (GRUB_TYPE_BITS (grub_uint64_t) - __builtin_clzll (n) - 1)
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