Re: [PATCH v2 1/1] x86, relocs: add function attributes to die()

[Nicolas Iooss]

Hello,

A few weeks ago I sent the patch below and got a review, but this patch
has not been applied yet in linux-next. Does it cause a problem I need
to fix?

Thanks,
Nicolas

On 05/09/16 17:28, Nilay Vaish wrote:
> On 4 September 2016 at 11:51, Nicolas Iooss <nicolas.iooss_linux@xxxxxxx> wrote:
>> When building the kernel with clang and some warning flags, the compiler
>> reports the following warning:
>>
>>     arch/x86/tools/relocs.c:979:6: warning: variable 'do_reloc' is used
>>     uninitialized whenever 'if' condition is false
>>     [-Wsometimes-uninitialized]
>>             if (!use_real_mode)
>>                 ^~~~~~~~~~~~~~
>>     arch/x86/tools/relocs.c:991:14: note: uninitialized use occurs here
>>             walk_relocs(do_reloc);
>>                         ^~~~~~~~
>>     arch/x86/tools/relocs.c:979:2: note: remove the 'if' if its
>>     condition is always true
>>             if (!use_real_mode)
>>             ^~~~~~~~~~~~~~~~~~~
>>     arch/x86/tools/relocs.c:976:24: note: initialize the variable
>>     'do_reloc' to silence this warning
>>                             const char *symname);
>>                                                 ^
>>                                                  = NULL
>>
>> This is obviously a false positive: whenever the 'if' condition is
>> false, the program calls die(). Nevertheless the compiler did not know
>> this call makes the program quit because this function did not have a
>> noreturn attribute. Add it.
>>
>> While at it, add a printf attribute too to die() and constify the format
>> parameter. This leads to some errors when compiling on x86_64:
>>
>>     arch/x86/tools/relocs.c:460:5: error: format specifies type 'int'
>>     but the argument has type 'Elf64_Xword' (aka 'unsigned long')
>>     [-Werror,-Wformat]
>>                                     sec->shdr.sh_size);
>>                                     ^~~~~~~~~~~~~~~~~
>>     arch/x86/tools/relocs.c:464:5: error: format specifies type 'int'
>>     but the argument has type 'Elf64_Off' (aka 'unsigned long')
>>     [-Werror,-Wformat]
>>                                     sec->shdr.sh_offset, strerror(errno));
>>                                     ^~~~~~~~~~~~~~~~~~~
>>
>> When relocs.c is included by relocs_32.c, sec->shdr.sh_size and
>> sec->shdr.sh_offset are 32-bit unsigned integers. When the file is
>> included by relocs_64.c, these expressions are 64-bit unsigned integers.
>>
>> Introduce a PRIuELF macro to define the right format to use when
>> printing these expressions.
>>
>> Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@xxxxxxx>
>> ---
>>  arch/x86/tools/relocs.c        | 14 +++++++-------
>>  arch/x86/tools/relocs.h        |  3 ++-
>>  arch/x86/tools/relocs_32.c     |  3 +++
>>  arch/x86/tools/relocs_64.c     |  3 +++
>>  arch/x86/tools/relocs_common.c |  2 +-
>>  5 files changed, 16 insertions(+), 9 deletions(-)
>>
>> diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
>> index 0c2fae8d929d..4cad603b8d58 100644
>> --- a/arch/x86/tools/relocs.c
>> +++ b/arch/x86/tools/relocs.c
>> @@ -397,7 +397,7 @@ static void read_shdrs(FILE *fp)
>>                     ehdr.e_shnum);
>>         }
>>         if (fseek(fp, ehdr.e_shoff, SEEK_SET) < 0) {
>> -               die("Seek to %d failed: %s\n",
>> +               die("Seek to %"PRIuELF" failed: %s\n",
>>                         ehdr.e_shoff, strerror(errno));
>>         }
>>         for (i = 0; i < ehdr.e_shnum; i++) {
>> @@ -431,11 +431,11 @@ static void read_strtabs(FILE *fp)
>>                 }
>>                 sec->strtab = malloc(sec->shdr.sh_size);
>>                 if (!sec->strtab) {
>> -                       die("malloc of %d bytes for strtab failed\n",
>> +                       die("malloc of %"PRIuELF" bytes for strtab failed\n",
>>                                 sec->shdr.sh_size);
>>                 }
>>                 if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0) {
>> -                       die("Seek to %d failed: %s\n",
>> +                       die("Seek to %"PRIuELF" failed: %s\n",
>>                                 sec->shdr.sh_offset, strerror(errno));
>>                 }
>>                 if (fread(sec->strtab, 1, sec->shdr.sh_size, fp)
>> @@ -456,11 +456,11 @@ static void read_symtabs(FILE *fp)
>>                 }
>>                 sec->symtab = malloc(sec->shdr.sh_size);
>>                 if (!sec->symtab) {
>> -                       die("malloc of %d bytes for symtab failed\n",
>> +                       die("malloc of %"PRIuELF" bytes for symtab failed\n",
>>                                 sec->shdr.sh_size);
>>                 }
>>                 if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0) {
>> -                       die("Seek to %d failed: %s\n",
>> +                       die("Seek to %"PRIuELF" failed: %s\n",
>>                                 sec->shdr.sh_offset, strerror(errno));
>>                 }
>>                 if (fread(sec->symtab, 1, sec->shdr.sh_size, fp)
>> @@ -489,11 +489,11 @@ static void read_relocs(FILE *fp)
>>                 }
>>                 sec->reltab = malloc(sec->shdr.sh_size);
>>                 if (!sec->reltab) {
>> -                       die("malloc of %d bytes for relocs failed\n",
>> +                       die("malloc of %"PRIuELF" bytes for relocs failed\n",
>>                                 sec->shdr.sh_size);
>>                 }
>>                 if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0) {
>> -                       die("Seek to %d failed: %s\n",
>> +                       die("Seek to %"PRIuELF" failed: %s\n",
>>                                 sec->shdr.sh_offset, strerror(errno));
>>                 }
>>                 if (fread(sec->reltab, 1, sec->shdr.sh_size, fp)
>> diff --git a/arch/x86/tools/relocs.h b/arch/x86/tools/relocs.h
>> index f59590645b68..6b7969719833 100644
>> --- a/arch/x86/tools/relocs.h
>> +++ b/arch/x86/tools/relocs.h
>> @@ -16,7 +16,8 @@
>>  #include <regex.h>
>>  #include <tools/le_byteshift.h>
>>
>> -void die(char *fmt, ...);
>> +__attribute__((format(printf, 1, 2))) __attribute__((noreturn))
>> +void die(const char *fmt, ...);
>>
>>  #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
>>
>> diff --git a/arch/x86/tools/relocs_32.c b/arch/x86/tools/relocs_32.c
>> index b2ade2bb4162..8024ec473e6a 100644
>> --- a/arch/x86/tools/relocs_32.c
>> +++ b/arch/x86/tools/relocs_32.c
>> @@ -14,4 +14,7 @@
>>  #define ELF_ST_BIND(o)         ELF32_ST_BIND(o)
>>  #define ELF_ST_VISIBILITY(o)   ELF32_ST_VISIBILITY(o)
>>
>> +/* printf format for Elf32_Off */
>> +#define PRIuELF PRIu32
>> +
>>  #include "relocs.c"
>> diff --git a/arch/x86/tools/relocs_64.c b/arch/x86/tools/relocs_64.c
>> index 56b61b743c4c..2cf4de5c9d99 100644
>> --- a/arch/x86/tools/relocs_64.c
>> +++ b/arch/x86/tools/relocs_64.c
>> @@ -14,4 +14,7 @@
>>  #define ELF_ST_BIND(o)          ELF64_ST_BIND(o)
>>  #define ELF_ST_VISIBILITY(o)    ELF64_ST_VISIBILITY(o)
>>
>> +/* printf format for Elf64_Off */
>> +#define PRIuELF PRIu64
>> +
>>  #include "relocs.c"
>> diff --git a/arch/x86/tools/relocs_common.c b/arch/x86/tools/relocs_common.c
>> index acab636bcb34..30adb44eff79 100644
>> --- a/arch/x86/tools/relocs_common.c
>> +++ b/arch/x86/tools/relocs_common.c
>> @@ -1,6 +1,6 @@
>>  #include "relocs.h"
>>
>> -void die(char *fmt, ...)
>> +void die(const char *fmt, ...)
>>  {
>>         va_list ap;
>>         va_start(ap, fmt);
>> --
>> 2.9.3
>>
> 
> I have to admit that this is the first time I am looking at these
> format specifier macros from inttypes.h.  I looked at that file.  Your
> usage seems correct to me and should achieve the desired outcome.
> 
> Reviewed-by: Nilay Vaish <nilayvaish@xxxxxxxxx>
>