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

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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: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/389962b1b702e3c78d169e59bcfac56282889173.1618331882.git.christophe.leroy@csgroup.eu
This commit is contained in:
Christophe Leroy 2021-04-13 16:38:10 +00:00 committed by Michael Ellerman
parent db87a71992
commit 1e688dd2a3
9 changed files with 72 additions and 25 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

2
arch/powerpc/include/asm/book3s/64/kup.h
View file

@ -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

54
arch/powerpc/include/asm/bug.h
View file

@ -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(); \
} else { \
BUG_ENTRY(PPC_TLNEI " %4, 0", \
BUGFLAG_WARNING | BUGFLAG_TAINT(TAINT_WARN), \
"r" (__ret_warn_on)); \
} \
__ret_warn_on = true; \
} else { \
__label__ __label_warn_on; \
\
WARN_ENTRY(PPC_TLNEI " %4, 0", \
BUGFLAG_WARNING | BUGFLAG_TAINT(TAINT_WARN), \
__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 */

14
arch/powerpc/include/asm/extable.h
View file

@ -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

11
arch/powerpc/include/asm/ppc_asm.h
View file

@ -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;) \

2
arch/powerpc/kernel/entry_64.S
View file

@ -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 */

2
arch/powerpc/kernel/misc_32.S
View file

@ -237,7 +237,7 @@ _GLOBAL(copy_page)
addi r3,r3,-4
0: twnei r5, 0 /* WARN if r3 is not cache aligned */
EMIT_BUG_ENTRY 0b,__FILE__,__LINE__, BUGFLAG_WARNING
EMIT_WARN_ENTRY 0b,__FILE__,__LINE__, BUGFLAG_WARNING
addi r4,r4,-4

9
arch/powerpc/kernel/traps.c
View file

@ -1477,8 +1477,13 @@ static void do_program_check(struct pt_regs *regs)
if (!(regs->msr & MSR_PR) && /* not user-mode */
report_bug(bugaddr, regs) == BUG_TRAP_TYPE_WARN) {
regs_add_return_ip(regs, 4);
return;
const struct exception_table_entry *entry;
entry = search_exception_tables(bugaddr);
if (entry) {
regs_set_return_ip(regs, extable_fixup(entry) + regs->nip - bugaddr);
return;
}
}
_exception(SIGTRAP, regs, TRAP_BRKPT, regs->nip);
return;

2
scripts/mod/modpost.c
View file

@ -931,7 +931,7 @@ static void check_section(const char *modname, struct elf_info *elf,
".kprobes.text", ".cpuidle.text", ".noinstr.text"
#define OTHER_TEXT_SECTIONS ".ref.text", ".head.text", ".spinlock.text", \
".fixup", ".entry.text", ".exception.text", ".text.*", \
".coldtext"
".coldtext", ".softirqentry.text"
#define INIT_SECTIONS ".init.*"
#define MEM_INIT_SECTIONS ".meminit.*"

1
tools/testing/selftests/powerpc/primitives/asm/extable.h Symbolic link
View file

@ -0,0 +1 @@
../../../../../../arch/powerpc/include/asm/extable.h