EDK2 builds with 'warning level 4' when using Microsoft tools. For the
most part, that enables desirable warnings similar to those provided by
gcc -Wall. There is one major difference though, Microsoft warning level
4 warns about the routine practice of assigning a larger size integer to
a smaller size integer. The Microsoft warning looks like:
warning C4244: conversion from 'UINT32' to 'UINT8', possible loss of data
Gcc has a warning option that is similar to Microsoft C4244: -WConversion
But the gcc option -Wall does _not_ enable -Wconversion. In fact, gcc
option -Wextra doesn't even enable -Wconversion. That suggests that
-Wconversion is a specialty warning not suitable for general use. EDK2
gcc builds do not enable -Wconversion.
I think Microsoft warning C4244 (and similar) should be removed from
EDK2 so that Microsoft warning settings are more consistent with gcc
warning settings. But that might be a difficult change to push through.
While it would be interesting to see what others think, completely
removing Microsoft Warning C4244 is a discussion for another day.
The immediate problem should be a lot easier to get agreement on. The
problem is that warning C4244 is buggy/imperfect in older Microsoft
compilers (DDK3790, VS2003, VS2005). As a result, some builds fail
with those compilers, but pass with newer ones. Here are examples:
OvmfPkg\Library\LoadLinuxLib\Linux.c(387)
OvmfPkg\Library\LoadLinuxLib\Linux.c(388)
OvmfPkg\VirtioBlkDxe\VirtioBlk.c(773)
OvmfPkg\VirtioBlkDxe\VirtioBlk.c(774)
OvmfPkg\VirtioNetDxe\DriverBinding.c(132)
OvmfPkg\VirtioScsiDxe\VirtioScsi.c(751)
StdLib\BsdSocketLib\res_mkupdate.c(186)
Here are code snippets that demonstrate the warning C4344 problem
with older Microsoft compilers:
#if defined (__GNUC__)
#include <stdint.h>
#else
#define uint16_t unsigned __int16
#define uint32_t unsigned __int32
#define uint64_t unsigned __int64
#endif
char test1 (int x) {return !x;}
char test2 (int x) {return x == 1;}
char test3 (int x) {return x & 1;}
uint32_t test4 (uint64_t x) {return x >> 32;}
uint32_t test5 (uint64_t x) {return x && 0xFFFFFFFF;}
enum {a=1, b=2}; uint16_t test6 (int x) {return x ? a : b;}
/*
W A R N I N G C O U N T S
Tool chain test1 test2 test3 test4 test5 test6
DDK3790 /W4 1 1 1 1 0 1
VS2003 /W4 1 1 1 1 0 1
VS2005 /W4 1 1 1 1 0 0
VS2008 /W4 0 0 0 0 0 0
VS2010 /W4 0 0 0 0 0 0
VS2012 /W4 0 0 0 0 0 0
VS2013 /W4 0 0 0 0 0 0
With VS2008 and newer, Microsoft compilers eliminate several
causes of unwanted warnings.
If others agree, I can make a BaseTools\Conf\tools_def.template patch to
disable warning C4244 for DDK3790, VS2003, and VS2005.
Thanks,
Scott
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