On 05.07.2022 05:54, Wei Chen wrote: > Xen uses "-fshort-wchar" in CFLAGS for EFI common code. Arm32 > is using stub.c of EFI common code for EFI stub functions. But > "-fshort-wchar" CFLAG will cause a warning when build stub.c > for Arm32: > "arm-linux-gnueabihf-ld: warning: arch/arm/efi/built_in.o uses > 2-byte wchar_t yet the output is to use 4-byte wchar_t; use of > wchar_t values across objects may fail" > > This is because the "-fshort-wchar" flag causes GCC to generate > code that is not binary compatible with code generated without > that flag. Why this warning hasn't been triggered in Arm64 is > because Arm64 does not use wchar type directly in any code for > parameters, variables and return values. And in EFI code, wchar > has been replaced by CHAR16 (the UEFI "abstraction" of wchar_t). > CHAR16 has been specified as unsigned short type in typedef, the > "-fshort-wchar" flag will not affect CHAR16. So Arm64 object > files are exactly the same with "-fshort-wchar" and without > "-fshort-wchar". > > We are also not using wchar in Arm32 codes, but Arm32 will embed > ABI information in ".ARM.attributes" section. This section stores > some object file attributes, like ABI version, CPU arch and etc. > And wchar size is described in this section by "Tag_ABI_PCS_wchar_t" > too. Tag_ABI_PCS_wchar_t is 2 for object files with "-fshort-wchar", > but for object files without "-fshort-wchar" is 4. Arm32 GCC > ld will check this tag, and throw above warning when it finds > the object files have different Tag_ABI_PCS_wchar_t values. > > As gnu-efi-3.0 use the GCC option "-fshort-wchar" to force wchar > to use short integers (2 bytes) instead of integers (4 bytes). > So keep "-fshort-wchar" for Xen EFI code is reasonable. In this > patch, we add "-fno-short-wchar" to override "-fshort-wchar" for Arm > architecutres without EFI enabled to remove above warning. > > Reported-and-Suggested-by: Jan Beulich <[email protected]> > Signed-off-by: Wei Chen <[email protected]>
Tested-by: Jan Beulich <[email protected]> As to the description: Why the reference to gnu-efi? I don't think it matters how they build their code? All that's important is what we do, I suppose. As to the title: I think the prefix would better be Arm32: (or alike). Hence how about "Arm32: avoid EFI stub wchar_t size linker warning"? Preferably with respective adjustments also: Reviewed-by: Jan Beulich <[email protected]> Jan
