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Merged
tavip merged 1 commit into from
Apr 6, 2025
Merged

lkl: Define symbols for string utilities #587

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1 change: 1 addition & 0 deletions arch/lkl/Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -61,6 +61,7 @@ LKL_ENTRY_POINTS += \
endif

core-y += arch/lkl/kernel/
core-y += arch/lkl/lib/
core-y += arch/lkl/mm/
core-y += arch/lkl/drivers/

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6 changes: 3 additions & 3 deletions arch/lkl/include/asm/string.h
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Expand Up @@ -8,6 +8,7 @@
/* use __mem* names to avoid conflict with KASAN's mem* functions. */

#define __HAVE_ARCH_MEMCPY
extern void *memcpy(void *dest, const void *src, size_t count);
static inline void *__memcpy(void *dest, const void *src, size_t count)
{
char *tmp = dest;
Expand All @@ -24,6 +25,7 @@ static inline void *__memcpy(void *dest, const void *src, size_t count)
}

#define __HAVE_ARCH_MEMSET
extern void *memset(void *s, int c, size_t count);
static inline void *__memset(void *s, int c, size_t count)
{
char *xs = s;
Expand All @@ -39,6 +41,7 @@ static inline void *__memset(void *s, int c, size_t count)
}

#define __HAVE_ARCH_MEMMOVE
extern void *memmove(void *dest, const void *src, size_t count);
static inline void *__memmove(void *dest, const void *src, size_t count)
{
char *tmp;
Expand Down Expand Up @@ -86,9 +89,6 @@ static inline void *__memmove(void *dest, const void *src, size_t count)
#undef memcpy
#undef memset
#undef memmove
extern void *memset(void *dst, int c, __kernel_size_t count);
extern void *memcpy(void *dst, const void *src, __kernel_size_t count);
extern void *memmove(void *dest, const void *src, size_t count);

#endif /* __SANITIZE_ADDRESS__ */

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3 changes: 3 additions & 0 deletions arch/lkl/lib/Makefile
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@@ -0,0 +1,3 @@
# SPDX-License-Identifier: GPL-2.0

obj-y += string.o
35 changes: 35 additions & 0 deletions arch/lkl/lib/string.c
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@@ -0,0 +1,35 @@
// SPDX-License-Identifier: GPL-2.0

#include <linux/string.h>
#include <linux/export.h>

#if !defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX)
/*
* If CONFIG_KASAN_GENERIC is on but CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX is
* off, mm/kasan/shadow.c will define the kasan version memcpy and its friends
* for us. We should not do anything, otherwise the symbols will conflict.
*/

#undef memcpy
#undef memset
#undef memmove

__visible void *memcpy(void *dest, const void *src, size_t count)
{
return __memcpy(dest, src, count);
}
EXPORT_SYMBOL(memcpy);
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@ddiss ddiss Apr 4, 2025

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Shouldn't this redirect already happen via the preprocessor using the #defines at https://github.com/lkl/linux/blob/master/arch/lkl/include/asm/string.h#L68 ? Are you building with or without CONFIG_KASAN?

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@lrh2000 lrh2000 Apr 4, 2025

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Shouldn't this redirect already happen via the preprocessor using the #defines at https://github.com/lkl/linux/blob/master/arch/lkl/include/asm/string.h#L68 ?

There is code that uses __builtin_memcpy directly. Our #define memcpy will have no effect on such usage. The compiler will generate direct calls to memcpy, which is an undefined symbol because we never define it.

linux/lib/string.c

Line 113 in 11f5b7e

__builtin_memcpy(dest, src, len);

Are you building with or without CONFIG_KASAN?

I built without CONFIG_KASAN and found these undefined symbols.

My patch was tested with and without CONFIG_KASAN. It should work either way.

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@ddiss ddiss Apr 4, 2025

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Thanks for the explanation, I wasn't familiar with how the compiler handled __builtin_memcpy. This change looks reasonable to me, although can't we now drop those #defines?

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@lrh2000 lrh2000 Apr 4, 2025 •
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Thanks for your review too!

can't we now drop those #defines?

I think it's okay. The only difference is that if we use static inline void *__memcpy(..) and #define memcpy __memcpy then most of memcpy will be inline, but if we have extern void *memcpy(..) then memcpy won't be inline.

I don't think the difference really matters here. I chose an implementation that requires minimal changes (and preserves the original inline semantics). But if we prefer to move the __memcpy implementation from string.h to string.c and then remove the #define altogether, I think that's perfectly fine and will update the patch accordingly.


__visible void *memset(void *s, int c, size_t count)
{
return __memset(s, c, count);
}
EXPORT_SYMBOL(memset);

__visible void *memmove(void *dest, const void *src, size_t count)
{
return __memmove(dest, src, count);
}
EXPORT_SYMBOL(memmove);

#endif
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