Re: [PATCH] powerpc/64: Fix build failure with GCC 8.1

From: Benjamin Herrenschmidt
Date: Mon May 28 2018 - 19:08:54 EST


On Mon, 2018-05-28 at 16:37 +0000, Christophe Leroy wrote:
> CC arch/powerpc/kernel/nvram_64.o
> arch/powerpc/kernel/nvram_64.c: In function 'nvram_create_partition':
> arch/powerpc/kernel/nvram_64.c:1042:2: error: 'strncpy' specified bound 12 equals destination size [-Werror=stringop-truncation]
> strncpy(new_part->header.name, name, 12);
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> CC arch/powerpc/kernel/trace/ftrace.o
> In function 'make_field',
> inlined from 'ps3_repository_read_boot_dat_address' at arch/powerpc/platforms/ps3/repository.c:900:9:
> arch/powerpc/platforms/ps3/repository.c:106:2: error: 'strncpy' output truncated before terminating nul copying 8 bytes from a string of the same length [-Werror=stringop-truncation]
> strncpy((char *)&n, text, 8);
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

That's not completely correct, here it's gcc warning being over-
zealous. The old specs I could find define the format to be a 12
characters strings *or* a less-than-12 characters NUL terminated
string. So it's perfectly ok to drop the trailing 0 if the name
happens to be exactly 12 characters.

Cheers,
Ben.

> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> ---
> arch/powerpc/kernel/nvram_64.c | 2 +-
> arch/powerpc/platforms/ps3/repository.c | 4 ++--
> 2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
> index ba681dac7b46..7507448cd904 100644
> --- a/arch/powerpc/kernel/nvram_64.c
> +++ b/arch/powerpc/kernel/nvram_64.c
> @@ -1039,7 +1039,7 @@ loff_t __init nvram_create_partition(const char *name, int sig,
> new_part->index = free_part->index;
> new_part->header.signature = sig;
> new_part->header.length = size;
> - strncpy(new_part->header.name, name, 12);
> + strncpy(new_part->header.name, name, sizeof(new_part->header.name) - 1);
> new_part->header.checksum = nvram_checksum(&new_part->header);
>
> rc = nvram_write_header(new_part);
> diff --git a/arch/powerpc/platforms/ps3/repository.c b/arch/powerpc/platforms/ps3/repository.c
> index 50dbaf24b1ee..b4d6628eec5e 100644
> --- a/arch/powerpc/platforms/ps3/repository.c
> +++ b/arch/powerpc/platforms/ps3/repository.c
> @@ -101,9 +101,9 @@ static u64 make_first_field(const char *text, u64 index)
>
> static u64 make_field(const char *text, u64 index)
> {
> - u64 n;
> + u64 n = 0;
>
> - strncpy((char *)&n, text, 8);
> + memcpy((char *)&n, text, min(sizeof(n), strlen(text)));
> return n + index;
> }
>