Re: gcc trunk fails to build kernel on PowerPC64 due to oprofile warnings

[William Cohen <wcohen@redhat.com>]

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On 01/25/2017 06:00 PM, Anton Blanchard wrote:
> Hi,
> 
> gcc trunk has failed to build PowerPC64 kernels for a month or so. The issue
> is in oprofile, which is common code but ends up being sucked into
> arch/powerpc and therefore subject to the -Werror applied to arch/powerpc:
>  
> linux/arch/powerpc/oprofile/../../../drivers/oprofile/oprofile_stats.c: In function ‘oprofile_create_stats_files’:
> linux/arch/powerpc/oprofile/../../../drivers/oprofile/oprofile_stats.c:55:25: error: ‘%d’ directive output may be truncated writing between 1 and 11 bytes into a region of size 7 [-Werror=format-truncation=]
>    snprintf(buf, 10, "cpu%d", i);
>                          ^~
> linux/arch/powerpc/oprofile/../../../drivers/oprofile/oprofile_stats.c:55:21: note: using the range [1, -2147483648] for directive argument
>    snprintf(buf, 10, "cpu%d", i);
>                      ^~~~~~~
> linux/arch/powerpc/oprofile/../../../drivers/oprofile/oprofile_stats.c:55:3: note: format output between 5 and 15 bytes into a destination of size 10
>    snprintf(buf, 10, "cpu%d", i);
>    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   LD      crypto/async_tx/built-in.o
>   CC      lib/random32.o
> cc1: all warnings being treated as errors
> 
> Anton
> 
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> 

The attached patch should make the buffer large enough to eliminate the warning.

-Will

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>From 7e46dbd7dc5bc941926a4a63c28ccebf46493e8d Mon Sep 17 00:00:00 2001
From: William Cohen <wcohen@redhat.com>
Date: Thu, 26 Jan 2017 10:33:59 -0500
Subject: [PATCH] Avoid hypthetical string truncation in oprofile stats buffer
MIME-Version: 1.0
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Increased the size of an internal oprofile driver buffer ensuring that
the string was never truncated for any possible int value to avoid the
following gcc-7 compiler error on ppc when building the kernel:

linux/arch/powerpc/oprofile/../../../drivers/oprofile/oprofile_stats.c: In function ‘oprofile_create_stats_files’:
linux/arch/powerpc/oprofile/../../../drivers/oprofile/oprofile_stats.c:55:25: error: ‘%d’ directive output may be truncated writing between 1 and 11 bytes into a region of size 7 [-Werror=format-truncation=]
   snprintf(buf, 10, "cpu%d", i);
                         ^~
linux/arch/powerpc/oprofile/../../../drivers/oprofile/oprofile_stats.c:55:21: note: using the range [1, -2147483648] for directive argument
   snprintf(buf, 10, "cpu%d", i);
                     ^~~~~~~
linux/arch/powerpc/oprofile/../../../drivers/oprofile/oprofile_stats.c:55:3: note: format output between 5 and 15 bytes into a destination of size 10
   snprintf(buf, 10, "cpu%d", i);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  LD      crypto/async_tx/built-in.o
  CC      lib/random32.o
cc1: all warnings being treated as errors

Signed-off-by: William Cohen <wcohen@redhat.com>
---
 drivers/oprofile/oprofile_stats.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/oprofile/oprofile_stats.c b/drivers/oprofile/oprofile_stats.c
index 59659ce..6fe7538 100644
--- a/drivers/oprofile/oprofile_stats.c
+++ b/drivers/oprofile/oprofile_stats.c
@@ -43,7 +43,7 @@ void oprofile_create_stats_files(struct dentry *root)
 	struct oprofile_cpu_buffer *cpu_buf;
 	struct dentry *cpudir;
 	struct dentry *dir;
-	char buf[10];
+	char buf[16];
 	int i;
 
 	dir = oprofilefs_mkdir(root, "stats");
@@ -52,7 +52,7 @@ void oprofile_create_stats_files(struct dentry *root)
 
 	for_each_possible_cpu(i) {
 		cpu_buf = &per_cpu(op_cpu_buffer, i);
-		snprintf(buf, 10, "cpu%d", i);
+		snprintf(buf, 16, "cpu%d", i);
 		cpudir = oprofilefs_mkdir(dir, buf);
 
 		/* Strictly speaking access to these ulongs is racy,
-- 
2.9.3