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

From: Nilay Vaish
Date: Mon Sep 05 2016 - 11:29:50 EST

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>