Unverified Commit 62135bf6 authored Apr 10, 2025 by Jisheng Zhang Committed by Palmer Dabbelt May 08, 2025

riscv: uaccess: use input constraints for ptr of __put_user()

Putting ptr in the inputs as opposed to output may seem incorrect but
this is done for a few reasons:
- Not having it in the output permits the use of asm goto in a
  subsequent patch. There are bugs in gcc [1] which would otherwise
  prevent it.
- Since the output memory is userspace there isn't any real benefit from
  telling the compiler about the memory clobber.
- x86, arm and powerpc all use this technique.

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113921

 # 1

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
[Cyril Bur: Rewritten commit message]
Signed-off-by: Cyril Bur <cyrilbur@tenstorrent.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250410070526.3160847-4-cyrilbur@tenstorrent.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

parent 19500c6d

arch/riscv/include/asm/uaccess.h

+9 −9

Original line number	Diff line number	Diff line
		@@ -219,11 +219,11 @@ do { \
		__typeof__(*(ptr)) __x = x; \
		__asm__ __volatile__ ( \
		"1:\n" \
		" " insn " %z2, %1\n" \
		" " insn " %z1, %2\n" \
		"2:\n" \
		_ASM_EXTABLE_UACCESS_ERR(1b, 2b, %0) \
		: "+r" (err), "=m" (*(ptr)) \
		: "rJ" (__x)); \
		: "+r" (err) \
		: "rJ" (__x), "m"(*(ptr))); \
		} while (0)

		#ifdef CONFIG_64BIT
		@@ -236,16 +236,16 @@ do { \
		u64 __x = (__typeof__((x)-(x)))(x); \
		__asm__ __volatile__ ( \
		"1:\n" \
		" sw %z3, %1\n" \
		" sw %z1, %3\n" \
		"2:\n" \
		" sw %z4, %2\n" \
		" sw %z2, %4\n" \
		"3:\n" \
		_ASM_EXTABLE_UACCESS_ERR(1b, 3b, %0) \
		_ASM_EXTABLE_UACCESS_ERR(2b, 3b, %0) \
		: "+r" (err), \
		"=m" (__ptr[__LSW]), \
		"=m" (__ptr[__MSW]) \
		: "rJ" (__x), "rJ" (__x >> 32)); \
		: "+r" (err) \
		: "rJ" (__x), "rJ" (__x >> 32), \
		"m" (__ptr[__LSW]), \
		"m" (__ptr[__MSW])); \
		} while (0)
		#endif /* CONFIG_64BIT */