Re: [Xen-devel] [PATCH] x86-64/EFI: add -fno-stack-protector to EFI build

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 08/14/2012 10:19 AM, Jan Beulich wrote:
>>>> On 14.08.12 at 15:52, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> wrote:
>> Otherwise, the build fails due to a missing __stack_chk_fail symbol.
>>
>> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
>> ---
>>  xen/arch/x86/efi/Makefile | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/xen/arch/x86/efi/Makefile b/xen/arch/x86/efi/Makefile
>> index 005e3e0..b727757 100644
>> --- a/xen/arch/x86/efi/Makefile
>> +++ b/xen/arch/x86/efi/Makefile
>> @@ -1,11 +1,11 @@
>> -CFLAGS += -fshort-wchar
>> +CFLAGS += -fshort-wchar -fno-stack-protector
> 
> It shouldn't be needed here (or else the rest of the Xen build
> should fail too). Or where would that symbol magically come
> from?

You are correct, this change is not needed. The Xen build already adds
-fno-stack-protector to CFLAGS, so this change would just duplicate it.

>>  obj-y += stub.o
>>  
>>  create = test -e $(1) || touch -t 199901010000 $(1)
>>  
>>  efi := $(filter y,$(x86_64)$(shell rm -f disabled))
>> -efi := $(if $(efi),$(shell $(CC) -c -Werror check.c 2>disabled && echo y))
>> +efi := $(if $(efi),$(shell $(CC) -fno-stack-protector -c -Werror check.c 
>> 2>disabled && echo y))
> 
> I can see why it might be needed here, albeit I'm curious why
> this is not a problem for our builds: Are you having a compiler
> in use that had been configured in a non-standard way? Plus
> I first want to understand why this special option isn't needed
> for the rest of the build tree.
> 
> Jan

This build was done on Gentoo using a hardened profile, which I assume
adds -fstack-protector to the default compiler flags. Compiler version
string is "gcc version 4.6.3 (Gentoo Hardened 4.6.3 p1.6, pie-0.5.2)"


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