[Xen-devel] [PATCH v3] tools: fix several "format-truncation" warnings with GCC 7

[Zhongze Liu <blackskygg@xxxxxxxxx>]

GCC 7.1.1 complains that several buffers passed to snprintf() in xenpmd
and tools/ocmal/xc are too small to hold the largest possible resulting string,
which is calculated by adding up the maximum length of all the substrings.

The warnings are treated as errors by -Werror, and goes like this (abbreviated):

xenpmd.c:94:36: error: ‘%s’ directive output may be truncated writing up to
255 bytes into a region of size 13 [-Werror=format-truncation=]
     #define BATTERY_INFO_FILE_PATH "/proc/acpi/battery/%s/info"
                                    ^
xenpmd.c:113:13: note: ‘snprintf’ output between 25 and 280 bytes into a
destination of size 32

xenpmd.c:95:37: error: ‘%s’ directive output may be truncated writing up to
255 bytes into a region of size 13 [-Werror=format-truncation=]
     #define BATTERY_STATE_FILE_PATH "/proc/acpi/battery/%s/state"
                                     ^
xenpmd.c:116:13: note: ‘snprintf’ output between 26 and 281 bytes into a
destination of size 32

xenctrl_stubs.c:65:15: error: ‘%s’ directive output may be truncated writing
up to 1023 bytes into a region of size 252 [-Werror=format-truncation=]
      "%d: %s: %s", error->code,
               ^~
xenctrl_stubs.c:64:4: note: ‘snprintf’ output 5 or more bytes (assuming 1028)
into a destination of size 256

Enlarge the size of these buffers as suggested by the complier
(and slightly rounded) to fix the warnings.

No functional changes.

Signed-off-by: Zhongze Liu <blackskygg@xxxxxxxxx>
Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
CC: David Scott <dave@xxxxxxxxxx>
CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>

Changed since v2:
  * Decrease the size of the file_name[] buffer properly to save more space.
  * Explain how the new sizes of the buffers are chosen in the commit message.
  * Include part of the error messages in the commit message.

Changed since v1:
  * Changed the word "error" to "warning" in title and description
  * Enlarge the buffer instead of replacing snprintf() with asprintf()
---
 tools/ocaml/libs/xc/xenctrl_stubs.c | 2 +-
 tools/xenpmd/xenpmd.c               | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/ocaml/libs/xc/xenctrl_stubs.c 
b/tools/ocaml/libs/xc/xenctrl_stubs.c
index 5e455519d4..f1b28db53a 100644
--- a/tools/ocaml/libs/xc/xenctrl_stubs.c
+++ b/tools/ocaml/libs/xc/xenctrl_stubs.c
@@ -54,7 +54,7 @@
 
 static void Noreturn failwith_xc(xc_interface *xch)
 {
-       char error_str[256];
+       char error_str[1028];
        if (xch) {
                const xc_error *error = xc_get_last_error(xch);
                if (error->code == XC_ERROR_NONE)
diff --git a/tools/xenpmd/xenpmd.c b/tools/xenpmd/xenpmd.c
index b3a31062aa..689c8fd670 100644
--- a/tools/xenpmd/xenpmd.c
+++ b/tools/xenpmd/xenpmd.c
@@ -100,7 +100,7 @@ FILE *get_next_battery_file(DIR *battery_dir,
 {
     FILE *file = 0;
     struct dirent *dir_entries;
-    char file_name[32];
+    char file_name[284];
     
     do 
     {
@@ -110,10 +110,10 @@ FILE *get_next_battery_file(DIR *battery_dir,
         if ( strlen(dir_entries->d_name) < 4 )
             continue;
         if ( battery_info_type == BIF ) 
-            snprintf(file_name, 32, BATTERY_INFO_FILE_PATH,
+            snprintf(file_name, sizeof(file_name), BATTERY_INFO_FILE_PATH,
                      dir_entries->d_name);
         else 
-            snprintf(file_name, 32, BATTERY_STATE_FILE_PATH,
+            snprintf(file_name, sizeof(file_name), BATTERY_STATE_FILE_PATH,
                      dir_entries->d_name);
         file = fopen(file_name, "r");
     } while ( !file );
-- 
2.13.1


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