Commit 1e688dd2 authored by Christophe Leroy's avatar Christophe Leroy Committed by Michael Ellerman
Browse files

powerpc/bug: Provide better flexibility to WARN_ON/__WARN_FLAGS() with asm goto 



Using asm goto in __WARN_FLAGS() and WARN_ON() allows more
flexibility to GCC.

For that add an entry to the exception table so that
program_check_exception() knowns where to resume execution
after a WARNING.

Here are two exemples. The first one is done on PPC32 (which
benefits from the previous patch), the second is on PPC64.

	unsigned long test(struct pt_regs *regs)
	{
		int ret;

		WARN_ON(regs->msr & MSR_PR);

		return regs->gpr[3];
	}

	unsigned long test9w(unsigned long a, unsigned long b)
	{
		if (WARN_ON(!b))
			return 0;
		return a / b;
	}

Before the patch:

	000003a8 <test>:
	 3a8:	81 23 00 84 	lwz     r9,132(r3)
	 3ac:	71 29 40 00 	andi.   r9,r9,16384
	 3b0:	40 82 00 0c 	bne     3bc <test+0x14>
	 3b4:	80 63 00 0c 	lwz     r3,12(r3)
	 3b8:	4e 80 00 20 	blr

	 3bc:	0f e0 00 00 	twui    r0,0
	 3c0:	80 63 00 0c 	lwz     r3,12(r3)
	 3c4:	4e 80 00 20 	blr

	0000000000000bf0 <.test9w>:
	 bf0:	7c 89 00 74 	cntlzd  r9,r4
	 bf4:	79 29 d1 82 	rldicl  r9,r9,58,6
	 bf8:	0b 09 00 00 	tdnei   r9,0
	 bfc:	2c 24 00 00 	cmpdi   r4,0
	 c00:	41 82 00 0c 	beq     c0c <.test9w+0x1c>
	 c04:	7c 63 23 92 	divdu   r3,r3,r4
	 c08:	4e 80 00 20 	blr

	 c0c:	38 60 00 00 	li      r3,0
	 c10:	4e 80 00 20 	blr

After the patch:

	000003a8 <test>:
	 3a8:	81 23 00 84 	lwz     r9,132(r3)
	 3ac:	71 29 40 00 	andi.   r9,r9,16384
	 3b0:	40 82 00 0c 	bne     3bc <test+0x14>
	 3b4:	80 63 00 0c 	lwz     r3,12(r3)
	 3b8:	4e 80 00 20 	blr

	 3bc:	0f e0 00 00 	twui    r0,0

	0000000000000c50 <.test9w>:
	 c50:	7c 89 00 74 	cntlzd  r9,r4
	 c54:	79 29 d1 82 	rldicl  r9,r9,58,6
	 c58:	0b 09 00 00 	tdnei   r9,0
	 c5c:	7c 63 23 92 	divdu   r3,r3,r4
	 c60:	4e 80 00 20 	blr

	 c70:	38 60 00 00 	li      r3,0
	 c74:	4e 80 00 20 	blr

In the first exemple, we see GCC doesn't need to duplicate what
happens after the trap.

In the second exemple, we see that GCC doesn't need to emit a test
and a branch in the likely path in addition to the trap.

We've got some WARN_ON() in .softirqentry.text section so it needs
to be added in the OTHER_TEXT_SECTIONS in modpost.c

Signed-off-by: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/389962b1b702e3c78d169e59bcfac56282889173.1618331882.git.christophe.leroy@csgroup.eu
parent db87a719

arch/powerpc/include/asm/book3s/64/kup.h

+1 −1
Original line number Diff line number Diff line
@@ -90,7 +90,7 @@ 
	/* Prevent access to userspace using any key values */

	LOAD_REG_IMMEDIATE(\gpr2, AMR_KUAP_BLOCKED)

999:	tdne	\gpr1, \gpr2

	EMIT_BUG_ENTRY 999b, __FILE__, __LINE__, (BUGFLAG_WARNING | BUGFLAG_ONCE)

	EMIT_WARN_ENTRY 999b, __FILE__, __LINE__, (BUGFLAG_WARNING | BUGFLAG_ONCE)

	END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_BOOK3S_KUAP, 67)

#endif

.endm

arch/powerpc/include/asm/bug.h

+45 −9
Original line number Diff line number Diff line
@@ -4,6 +4,7 @@ 
#ifdef __KERNEL__



#include <asm/asm-compat.h>

#include <asm/extable.h>



#ifdef CONFIG_BUG
@@ -30,6 +31,11 @@ 
.endm

#endif /* verbose */



.macro EMIT_WARN_ENTRY addr,file,line,flags

	EX_TABLE(\addr,\addr+4)

	EMIT_BUG_ENTRY \addr,\file,\line,\flags

.endm



#else /* !__ASSEMBLY__ */

/* _EMIT_BUG_ENTRY expects args %0,%1,%2,%3 to be FILE, LINE, flags and

   sizeof(struct bug_entry), respectively */
@@ -58,6 +64,16 @@ 
		  "i" (sizeof(struct bug_entry)),	\

		  ##__VA_ARGS__)



#define WARN_ENTRY(insn, flags, label, ...)		\

	asm_volatile_goto(				\

		"1:	" insn "\n"			\

		EX_TABLE(1b, %l[label])			\

		_EMIT_BUG_ENTRY				\

		: : "i" (__FILE__), "i" (__LINE__),	\

		  "i" (flags),				\

		  "i" (sizeof(struct bug_entry)),	\

		  ##__VA_ARGS__ : : label)



/*

 * BUG_ON() and WARN_ON() do their best to cooperate with compile-time

 * optimisations. However depending on the complexity of the condition
@@ -70,7 +86,15 @@ 
} while (0)

#define HAVE_ARCH_BUG



#define __WARN_FLAGS(flags) BUG_ENTRY("twi 31, 0, 0", BUGFLAG_WARNING | (flags))

#define __WARN_FLAGS(flags) do {				\

	__label__ __label_warn_on;				\

								\

	WARN_ENTRY("twi 31, 0, 0", BUGFLAG_WARNING | (flags), __label_warn_on); \

	unreachable();						\

								\

__label_warn_on:						\

	break;							\

} while (0)



#ifdef CONFIG_PPC64

#define BUG_ON(x) do {						\
@@ -83,15 +107,24 @@ 
} while (0)



#define WARN_ON(x) ({						\

	int __ret_warn_on = !!(x);				\

	if (__builtin_constant_p(__ret_warn_on)) {		\

		if (__ret_warn_on)				\

	bool __ret_warn_on = false;				\

	do {							\

		if (__builtin_constant_p((x))) {		\

			if (!(x)) 				\

				break; 				\

			__WARN();				\

			__ret_warn_on = true;			\

		} else {					\

		BUG_ENTRY(PPC_TLNEI " %4, 0",			\

			__label__ __label_warn_on;		\

								\

			WARN_ENTRY(PPC_TLNEI " %4, 0",		\

				   BUGFLAG_WARNING | BUGFLAG_TAINT(TAINT_WARN),	\

			  "r" (__ret_warn_on));	\

				   __label_warn_on, "r" (x));	\

			break;					\

__label_warn_on:						\

			__ret_warn_on = true;			\

		}						\

	} while (0);						\

	unlikely(__ret_warn_on);				\

})
@@ -104,8 +137,11 @@ 
#ifdef __ASSEMBLY__

.macro EMIT_BUG_ENTRY addr,file,line,flags

.endm

.macro EMIT_WARN_ENTRY addr,file,line,flags

.endm

#else /* !__ASSEMBLY__ */

#define _EMIT_BUG_ENTRY

#define _EMIT_WARN_ENTRY

#endif

#endif /* CONFIG_BUG */

arch/powerpc/include/asm/extable.h

+14 −0
Original line number Diff line number Diff line
@@ -17,6 +17,8 @@ 


#define ARCH_HAS_RELATIVE_EXTABLE



#ifndef __ASSEMBLY__



struct exception_table_entry {

	int insn;

	int fixup;
@@ -28,3 +30,15 @@ static inline unsigned long extable_fixup(const struct exception_table_entry *x) 
}



#endif



/*

 * Helper macro for exception table entries

 */

#define EX_TABLE(_fault, _target)		\

	stringify_in_c(.section __ex_table,"a";)\

	stringify_in_c(.balign 4;)		\

	stringify_in_c(.long (_fault) - . ;)	\

	stringify_in_c(.long (_target) - . ;)	\

	stringify_in_c(.previous)



#endif

arch/powerpc/include/asm/ppc_asm.h

+1 −10
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <asm/ppc-opcode.h>

#include <asm/firmware.h>

#include <asm/feature-fixups.h>

#include <asm/extable.h>



#ifdef __ASSEMBLY__
@@ -752,16 +753,6 @@ END_FTR_SECTION_NESTED(CPU_FTR_CELL_TB_BUG, CPU_FTR_CELL_TB_BUG, 96) 


#endif /*  __ASSEMBLY__ */



/*

 * Helper macro for exception table entries

 */

#define EX_TABLE(_fault, _target)		\

	stringify_in_c(.section __ex_table,"a";)\

	stringify_in_c(.balign 4;)		\

	stringify_in_c(.long (_fault) - . ;)	\

	stringify_in_c(.long (_target) - . ;)	\

	stringify_in_c(.previous)



#define SOFT_MASK_TABLE(_start, _end)		\

	stringify_in_c(.section __soft_mask_table,"a";)\

	stringify_in_c(.balign 8;)		\

arch/powerpc/kernel/entry_64.S

+1 −1
Original line number Diff line number Diff line
@@ -309,7 +309,7 @@ _GLOBAL(enter_rtas) 
	 */

	lbz	r0,PACAIRQSOFTMASK(r13)

1:	tdeqi	r0,IRQS_ENABLED

	EMIT_BUG_ENTRY 1b,__FILE__,__LINE__,BUGFLAG_WARNING

	EMIT_WARN_ENTRY 1b,__FILE__,__LINE__,BUGFLAG_WARNING

#endif



	/* Hard-disable interrupts */