[PATCH][next] MIPS: dec: prom: Address -Warray-bounds warning

[PATCH][next] MIPS: dec: prom: Address -Warray-bounds warning

[Gustavo A. R. Silva]

Zero-length arrays are deprecated, and we are replacing them with flexible
array members instead. So, replace zero-length array with flexible-array
member in struct memmap.

Address the following warning found after building (with GCC-13) mips64
with decstation_64_defconfig:
In function 'rex_setup_memory_region',
    inlined from 'prom_meminit' at arch/mips/dec/prom/memory.c:91:3:
arch/mips/dec/prom/memory.c:72:31: error: array subscript i is outside array bounds of 'unsigned char[0]' [-Werror=array-bounds=]
   72 |                 if (bm->bitmap[i] == 0xff)
      |                     ~~~~~~~~~~^~~
In file included from arch/mips/dec/prom/memory.c:16:
./arch/mips/include/asm/dec/prom.h: In function 'prom_meminit':
./arch/mips/include/asm/dec/prom.h:73:23: note: while referencing 'bitmap'
   73 |         unsigned char bitmap[0];

This helps with the ongoing efforts to globally enable -Warray-bounds.

This results in no differences in binary output.

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/323
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 arch/mips/include/asm/dec/prom.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/dec/prom.h b/arch/mips/include/asm/dec/prom.h
index 1e1247add1cf..908e96e3a311 100644
--- a/arch/mips/include/asm/dec/prom.h
+++ b/arch/mips/include/asm/dec/prom.h
@@ -70,7 +70,7 @@ static inline bool prom_is_rex(u32 magic)
  */
 typedef struct {
 	int pagesize;
-	unsigned char bitmap[0];
+	unsigned char bitmap[];
 } memmap;
 
 
-- 
2.34.1

Re: [PATCH][next] MIPS: dec: prom: Address -Warray-bounds warning

[Thomas Bogendoerfer]

On Thu, Jun 22, 2023 at 05:43:57PM -0600, Gustavo A. R. Silva wrote:
> Zero-length arrays are deprecated, and we are replacing them with flexible
> array members instead. So, replace zero-length array with flexible-array
> member in struct memmap.
> 
> Address the following warning found after building (with GCC-13) mips64
> with decstation_64_defconfig:
> In function 'rex_setup_memory_region',
>     inlined from 'prom_meminit' at arch/mips/dec/prom/memory.c:91:3:
> arch/mips/dec/prom/memory.c:72:31: error: array subscript i is outside array bounds of 'unsigned char[0]' [-Werror=array-bounds=]
>    72 |                 if (bm->bitmap[i] == 0xff)
>       |                     ~~~~~~~~~~^~~
> In file included from arch/mips/dec/prom/memory.c:16:
> ./arch/mips/include/asm/dec/prom.h: In function 'prom_meminit':
> ./arch/mips/include/asm/dec/prom.h:73:23: note: while referencing 'bitmap'
>    73 |         unsigned char bitmap[0];
> 
> This helps with the ongoing efforts to globally enable -Warray-bounds.
> 
> This results in no differences in binary output.
> 
> Link: https://github.com/KSPP/linux/issues/79
> Link: https://github.com/KSPP/linux/issues/323
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
>  arch/mips/include/asm/dec/prom.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/mips/include/asm/dec/prom.h b/arch/mips/include/asm/dec/prom.h
> index 1e1247add1cf..908e96e3a311 100644
> --- a/arch/mips/include/asm/dec/prom.h
> +++ b/arch/mips/include/asm/dec/prom.h
> @@ -70,7 +70,7 @@ static inline bool prom_is_rex(u32 magic)
>   */
>  typedef struct {
>  	int pagesize;
> -	unsigned char bitmap[0];
> +	unsigned char bitmap[];
>  } memmap;
>  
>  
> -- 
> 2.34.1

applied to mips-next.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]

Re: [PATCH][next] MIPS: dec: prom: Address -Warray-bounds warning

[Maciej W. Rozycki]

On Fri, 23 Jun 2023, Thomas Bogendoerfer wrote:

> > Zero-length arrays are deprecated, and we are replacing them with flexible
> > array members instead. So, replace zero-length array with flexible-array
> > member in struct memmap.

 Technically it is a semantics bug fix actually, as the TURBOchannel 
firmware specification (from Jan 1993) says it's:

typedef struct{ int pagesize; unsigned char bitmap[];}memmap;
int getbitmap(memmap *map);

(formatting preserved as in the document) so it should have always been a 
flexible array member.  Maybe old (2.x) GCC versions had an issue with it 
or something, as otherwise I can't imagine why whoever added our typedef 
did it differently from the spec.

> applied to mips-next.

 Not sure if you can retrofit it, but:

Acked-by: Maciej W. Rozycki <macro@orcam.me.uk>

  Maciej

Re: [PATCH][next] MIPS: dec: prom: Address -Warray-bounds warning

[Gustavo A. R. Silva]

On 6/23/23 07:41, Maciej W. Rozycki wrote:
> On Fri, 23 Jun 2023, Thomas Bogendoerfer wrote:
> 
>>> Zero-length arrays are deprecated, and we are replacing them with flexible
>>> array members instead. So, replace zero-length array with flexible-array
>>> member in struct memmap.
> 
>   Technically it is a semantics bug fix actually, as the TURBOchannel
> firmware specification (from Jan 1993) says it's:
> 
> typedef struct{ int pagesize; unsigned char bitmap[];}memmap;
> int getbitmap(memmap *map);
> 
> (formatting preserved as in the document) so it should have always been a
> flexible array member.  Maybe old (2.x) GCC versions had an issue with it
> or something, as otherwise I can't imagine why whoever added our typedef
> did it differently from the spec.

Apparently, flexible-array members were supported in some 2.x versions as an
extension to the language; and it was not until GCC 3.0 that they were fully
supported by the compiler.

> 
>> applied to mips-next.
> 
>   Not sure if you can retrofit it, but:
> 
> Acked-by: Maciej W. Rozycki <macro@orcam.me.uk>

Thanks!
--
Gustavo