linux-kernel - [PATCH 3.16 124/178] powerpc/kernel: Use kprobe blacklist for asm functions

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Date:   Sun, 16 Jul 2017 14:56:46 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Michael Ellerman" <mpe@...erman.id.au>,
        "Nicholas Piggin" <npiggin@...il.com>
Subject: [PATCH 3.16 124/178] powerpc/kernel: Use kprobe blacklist for asm
 functions

3.16.46-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Nicholas Piggin <npiggin@...il.com>

commit 6f698df10cb24d466b9a790b9daedb9e7bcd5d2a upstream.

Rather than forcing the whole function into the ".kprobes.text" section,
just add the symbol's address to the kprobe blacklist.

This also lets us drop the three versions of the_KPROBE macro, in
exchange for just one version of _ASM_NOKPROBE_SYMBOL - which is a good
cleanup.

Signed-off-by: Nicholas Piggin <npiggin@...il.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/powerpc/include/asm/ppc_asm.h | 40 +++++++++++++-------------------------
 arch/powerpc/kernel/misc_32.S      |  4 +++-
 arch/powerpc/kernel/misc_64.S      |  5 +++--
 3 files changed, 20 insertions(+), 29 deletions(-)

--- a/arch/powerpc/include/asm/ppc_asm.h
+++ b/arch/powerpc/include/asm/ppc_asm.h
@@ -217,13 +217,6 @@ name: \
 	addi r2,r2,(.TOC.-0b)@l; \
 	.localentry name,.-name
 
-#define _KPROBE(name) \
-	.section ".kprobes.text","a"; \
-	.align 2 ; \
-	.type name,@function; \
-	.globl name; \
-name:
-
 #define DOTSYM(a)	a
 
 #else
@@ -247,20 +240,6 @@ GLUE(.,name):
 
 #define _GLOBAL_TOC(name) _GLOBAL(name)
 
-#define _KPROBE(name) \
-	.section ".kprobes.text","a"; \
-	.align 2 ; \
-	.globl name; \
-	.globl GLUE(.,name); \
-	.section ".opd","aw"; \
-name: \
-	.quad GLUE(.,name); \
-	.quad .TOC.@...base; \
-	.quad 0; \
-	.previous; \
-	.type GLUE(.,name),@function; \
-GLUE(.,name):
-
 #define DOTSYM(a)	GLUE(.,a)
 
 #endif
@@ -279,13 +258,22 @@ n:
 
 #define _GLOBAL_TOC(name) _GLOBAL(name)
 
-#define _KPROBE(n)	\
-	.section ".kprobes.text","a";	\
-	.globl	n;	\
-n:
-
 #endif
 
+/*
+ * __kprobes (the C annotation) puts the symbol into the .kprobes.text
+ * section, which gets emitted at the end of regular text.
+ *
+ * _ASM_NOKPROBE_SYMBOL and NOKPROBE_SYMBOL just adds the symbol to
+ * a blacklist. The former is for core kprobe functions/data, the
+ * latter is for those that incdentially must be excluded from probing
+ * and allows them to be linked at more optimal location within text.
+ */
+#define _ASM_NOKPROBE_SYMBOL(entry)			\
+	.pushsection "_kprobe_blacklist","aw";		\
+	PPC_LONG (entry) ;				\
+	.popsection
+
 /* 
  * LOAD_REG_IMMEDIATE(rn, expr)
  *   Loads the value of the constant expression 'expr' into register 'rn'
--- a/arch/powerpc/kernel/misc_32.S
+++ b/arch/powerpc/kernel/misc_32.S
@@ -345,7 +345,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_UNIFIED_ID
  *
  * flush_icache_range(unsigned long start, unsigned long stop)
  */
-_KPROBE(flush_icache_range)
+_GLOBAL(flush_icache_range)
 BEGIN_FTR_SECTION
 	PURGE_PREFETCHED_INS
 	blr				/* for 601, do nothing */
@@ -376,6 +376,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_COHERENT_I
 	sync				/* additional sync needed on g4 */
 	isync
 	blr
+_ASM_NOKPROBE_SYMBOL(flush_icache_range)
+
 /*
  * Write any modified data cache blocks out to memory.
  * Does not invalidate the corresponding cache lines (especially for
--- a/arch/powerpc/kernel/misc_64.S
+++ b/arch/powerpc/kernel/misc_64.S
@@ -65,7 +65,7 @@ PPC64_CACHES:
  *   flush all bytes from start through stop-1 inclusive
  */
 
-_KPROBE(flush_icache_range)
+_GLOBAL(flush_icache_range)
 BEGIN_FTR_SECTION
 	PURGE_PREFETCHED_INS
 	blr
@@ -108,7 +108,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_COHERENT_I
 	bdnz	2b
 	isync
 	blr
-	.previous .text
+_ASM_NOKPROBE_SYMBOL(flush_icache_range)
+
 /*
  * Like above, but only do the D-cache.
  *