Re: [PATCH V2 1/2] BaseTools: Add gcc flag to warn on void* pointer arithmetic

["Bob Feng" <bob.c.feng@intel.com>]

Reviewed-by: Bob Feng<bob.c.feng@intel.com>


-----Original Message-----
From: PierreGondois <pierre.gondois@arm.com> 
Sent: Tuesday, July 7, 2020 4:35 PM
To: devel@edk2.groups.io
Cc: Pierre Gondois <Pierre.Gondois@arm.com>; Feng, Bob C <bob.c.feng@intel.com>; Gao, Liming <liming.gao@intel.com>; tomas.pilar@arm.com; nd@arm.com
Subject: [PATCH V2 1/2] BaseTools: Add gcc flag to warn on void* pointer arithmetic

From: Pierre Gondois <pierre.gondois@arm.com>

By default, gcc allows void* pointer arithmetic.
This is a GCC extension.
However:
 - the C reference manual states that void*
   pointer "cannot be operands of addition
   or subtraction operators". Cf s5.3.1
   "Generic Pointers";
 - Visual studio compiler treat such operation as
   an error.

To prevent such pointer arithmetic, the "-Wpointer-arith"
flag should be set for all GCC versions.

The "-Wpointer-arith"  allows to:
  "Warn about anything that depends on the "size of"
  a function type or of void. GNU C assigns these
  types a size of 1, for convenience in calculations
  with void * pointers and pointers to functions."

This flag is available since GCC2.95.3 which came out in 2001.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
---

The changes can be seen at: https://github.com/PierreARM/edk2/commits/831_Add_gcc_flag_warning_v2

Notes:
    v1:
     - Add "-Wpointer-arith" gcc flag. [Pierre]
    v2:
     - Only add the flag for ARM and AARCH64. [Tomas]

 BaseTools/Conf/tools_def.template | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/BaseTools/Conf/tools_def.template b/BaseTools/Conf/tools_def.template
index 8aeb8a2a6417e41c5660cda5066f52adc8cc3089..397b011ba38f97f81f314f8641ac8bb95d5a2197 100755
--- a/BaseTools/Conf/tools_def.template
+++ b/BaseTools/Conf/tools_def.template
@@ -1,7 +1,7 @@
 #
 #  Copyright (c) 2006 - 2018, Intel Corporation. All rights reserved.<BR>  #  Portions copyright (c) 2008 - 2009, Apple Inc. All rights reserved.<BR> -#  Portions copyright (c) 2011 - 2019, ARM Ltd. All rights reserved.<BR>
+#  Portions copyright (c) 2011 - 2020, ARM Ltd. All rights 
+reserved.<BR>
 #  Copyright (c) 2015, Hewlett-Packard Development Company, L.P.<BR>  #  (C) Copyright 2020, Hewlett Packard Enterprise Development LP<BR>  #  Copyright (c) Microsoft Corporation
@@ -1921,9 +1921,9 @@ NOOPT_*_*_OBJCOPY_ADDDEBUGFLAG     = --add-gnu-debuglink=$(DEBUG_DIR)/$(MODULE_N
 DEFINE GCC_ALL_CC_FLAGS            = -g -Os -fshort-wchar -fno-builtin -fno-strict-aliasing -Wall -Werror -Wno-array-bounds -include AutoGen.h -fno-common
 DEFINE GCC_IA32_CC_FLAGS           = DEF(GCC_ALL_CC_FLAGS) -m32 -malign-double -freorder-blocks -freorder-blocks-and-partition -O2 -mno-stack-arg-probe
 DEFINE GCC_X64_CC_FLAGS            = DEF(GCC_ALL_CC_FLAGS) -mno-red-zone -Wno-address -mno-stack-arg-probe
-DEFINE GCC_ARM_CC_FLAGS            = DEF(GCC_ALL_CC_FLAGS) -mlittle-endian -mabi=aapcs -fno-short-enums -funsigned-char -ffunction-sections -fdata-sections -fomit-frame-pointer -Wno-address -mthumb -mfloat-abi=soft -fno-pic -fno-pie
+DEFINE GCC_ARM_CC_FLAGS            = DEF(GCC_ALL_CC_FLAGS) -Wpointer-arith -mlittle-endian -mabi=aapcs -fno-short-enums -funsigned-char -ffunction-sections -fdata-sections -fomit-frame-pointer -Wno-address -mthumb -mfloat-abi=soft -fno-pic -fno-pie
 DEFINE GCC_ARM_CC_XIPFLAGS         = -mno-unaligned-access
-DEFINE GCC_AARCH64_CC_FLAGS        = DEF(GCC_ALL_CC_FLAGS) -mlittle-endian -fno-short-enums -fverbose-asm -funsigned-char  -ffunction-sections -fdata-sections -Wno-address -fno-asynchronous-unwind-tables -fno-unwind-tables -fno-pic -fno-pie -ffixed-x18
+DEFINE GCC_AARCH64_CC_FLAGS        = DEF(GCC_ALL_CC_FLAGS) -Wpointer-arith -mlittle-endian -fno-short-enums -fverbose-asm -funsigned-char -ffunction-sections -fdata-sections -Wno-address -fno-asynchronous-unwind-tables -fno-unwind-tables -fno-pic -fno-pie -ffixed-x18
 DEFINE GCC_AARCH64_CC_XIPFLAGS     = -mstrict-align -mgeneral-regs-only
 DEFINE GCC_DLINK_FLAGS_COMMON      = -nostdlib --pie
 DEFINE GCC_DLINK2_FLAGS_COMMON     = -Wl,--script=$(EDK_TOOLS_PATH)/Scripts/GccBase.lds
--
'Guid(CE165669-3EF3-493F-B85D-6190EE5B9759)'