Re: [edk2-devel] [PATCH v1] BaseTools: Add gcc flag to warn on void* pointer arithmetic

["Tomas Pilar (tpilar)" <Tomas.Pilar@arm.com>]

It looks like GCC5_X64_CC_FLAGS pick up GCC48_ALL_CC_FLAGS as the lowest level flag list, so this change will not apply to compilations on the X64 architecture.

That said, I suspect that X64 architecture will likely have the biggest issues with disallowing void* arithmetic, so we either:

1. Mend the tools_def to make GCC48_ALL_CC_FLAGS pick up GCC_ALL_CC_FLAGS, rerun tests and CI to make sure this change does not break large parts of existing codebase.
2. Move this change to ARM/AARCH64 low level CC_FLAGS lists to explicitly exclude this change from X64 architecture compilation.

Cheers,
Tom

NB. I personally like the void* arithmetic GNU C extension - I like being able to combine the implicit pointer casts with raw pointer arithmetic. But I can appreciate if we want to keep the codebase strict.

-----Original Message-----
From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of PierreGondois via groups.io
Sent: 30 June 2020 16:24
To: devel@edk2.groups.io
Cc: Pierre Gondois <Pierre.Gondois@arm.com>; bob.c.feng@intel.com; liming.gao@intel.com; nd <nd@arm.com>
Subject: [edk2-devel] [PATCH v1] 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_v1
Notes:
    v1:
     - Add "-Wpointer-arith" gcc flag. [Pierre]

 BaseTools/Conf/tools_def.template | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/BaseTools/Conf/tools_def.template b/BaseTools/Conf/tools_def.template
index 8aeb8a2a6417e41c5660cda5066f52adc8cc3089..fba71665d6ade4dad08a5a0c343f357fd413a8a4 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
@@ -1918,7 +1918,7 @@ NOOPT_*_*_OBJCOPY_ADDDEBUGFLAG     = --add-gnu-debuglink=$(DEBUG_DIR)/$(MODULE_N
 *_*_*_DTCPP_PATH                   = DEF(DTCPP_BIN)
 *_*_*_DTC_PATH                     = DEF(DTC_BIN)
 
-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_ALL_CC_FLAGS            = -g -Os -fshort-wchar -fno-builtin -fno-strict-aliasing -Wall -Werror -Wpointer-arith -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
-- 
'Guid(CE165669-3EF3-493F-B85D-6190EE5B9759)'