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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

> 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 (unless we go the $(error ) route anyway).

Jan



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