Re: [Xen-devel] [PATCH v3 3/3] x86: check for multiboot{1, 2} header presence

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 27/06/2019 13:10, Jan Beulich wrote:
>>>> On 27.06.19 at 13:51, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 27/06/2019 10:33, Roger Pau Monne wrote:
>>> diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
>>> index 8a8d8f060f..94e6c9aee3 100644
>>> --- a/xen/arch/x86/Makefile
>>> +++ b/xen/arch/x86/Makefile
>>> @@ -99,9 +99,14 @@ endif
>>>  syms-warn-dup-y := --warn-dup
>>>  syms-warn-dup-$(CONFIG_SUPPRESS_DUPLICATE_SYMBOL_WARNINGS) :=
>>>  
>>> +$(TARGET): TMP = $(@D)/.$(@F)
>> I'd suggest giving this a .elf32 suffix to make it clear which pass of
>> the build it comes from.
>>
>>>  $(TARGET): $(TARGET)-syms $(efi-y) boot/mkelf32
>>> -   ./boot/mkelf32 $(notes_phdrs) $(TARGET)-syms $(TARGET) 
>>> $(XEN_IMG_OFFSET) \
>>> +   ./boot/mkelf32 $(notes_phdrs) $(TARGET)-syms $(TMP) $(XEN_IMG_OFFSET) \
>>>                    `$(NM) $(TARGET)-syms | sed -ne 's/^\([^ ]*\) . 
>>> __2M_rwdata_end$$/0x\1/p'`
>>> +   # Check for multiboot{1,2} headers
>>> +   od -t x4 -N 8192 $(TMP) | grep 1badb002 > /dev/null ||
>>> +   od -t x4 -N 32768 $(TMP) | grep e85250d6 > /dev/null
>> This works, but
>>
>> Makefile:104: recipe for target '/local/xen.git/xen/xen' failed
>>
>> Isn't helpful to identify what went wrong.  Sadly, we can't use $(error
>> ...) in a shell snippet,
> I think we could:
>
>        $(if $(shell od -t x4 -N 8192 $(TMP) | grep 1badb002),,$(error 
> ...)exit 1)
>
> But I admit I didn't check whether it is well defined that only one of
> the last two operands of $(if ) get actually evaluated.

Of the two options, I think the || { ; false } is clearer to follow.

>
>> but:
>>
>> andrewcoop@andrewcoop:/local/xen.git/xen$ git d
>> diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
>> index 94e6c9aee3..a1d6605a8b 100644
>> --- a/xen/arch/x86/Makefile
>> +++ b/xen/arch/x86/Makefile
>> @@ -99,13 +99,14 @@ endif
>>  syms-warn-dup-y := --warn-dup
>>  syms-warn-dup-$(CONFIG_SUPPRESS_DUPLICATE_SYMBOL_WARNINGS) :=
>>  
>> -$(TARGET): TMP = $(@D)/.$(@F)
>> +$(TARGET): TMP = $(@D)/.$(@F).elf32
>>  $(TARGET): $(TARGET)-syms $(efi-y) boot/mkelf32
>>         ./boot/mkelf32 $(notes_phdrs) $(TARGET)-syms $(TMP) 
>> $(XEN_IMG_OFFSET) \
>>                        `$(NM) $(TARGET)-syms | sed -ne 's/^\([^ ]*\) . 
>> __2M_rwdata_end$$/0x\1/p'`
>> -       # Check for multiboot{1,2} headers
>> -       od -t x4 -N 8192 $(TMP) | grep 1badb002 > /dev/null
>> -       od -t x4 -N 32768 $(TMP) | grep e85250d6 > /dev/null
>> +       od -t x4 -N 8192 $(TMP)  | grep 1badb002 > /dev/null || \
>> +               { echo "No Multiboot1 header found"; false; }
>> +       od -t x4 -N 32768 $(TMP) | grep e85250d6 > /dev/null || \
>> +               { echo "No Multiboot2 header found"; false; }
>>         mv $(TMP) $(TARGET)
>>  
>>  ALL_OBJS := $(BASEDIR)/arch/x86/boot/built_in.o 
>> $(BASEDIR)/arch/x86/efi/built_in.o $(ALL_OBJS)
>>
>> results in:
>>
>> No Multiboot1 header found
>> Makefile:104: recipe for target '/local/xen.git/xen/xen' failed
>> make[2]: *** [/local/xen.git/xen/xen] Error 1
>> Makefile:136: recipe for target '/local/xen.git/xen/xen' failed
>> make[1]: *** [/local/xen.git/xen/xen] Error 2
>> Makefile:45: recipe for target 'build' failed
>> make: *** [build] Error 2
>>
>> Which is far more clear.
>>
>> Thoughts?
> Good idea. The only further request I have is to add >&2 to the
> echo commands.

Done.

~Andrew

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