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

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Date:   Thu, 22 Jun 2023 17:43:57 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     "Maciej W. Rozycki" <macro@...am.me.uk>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org
Subject: [PATCH][next] MIPS: dec: prom: Address -Warray-bounds warning

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@...nel.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