Re: [Xen-devel] [PATCH v3 2/3] XENVER_build_id: Provide ld-embedded build-ids (v8)

[Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>]

>> --- a/Config.mk
>> +++ b/Config.mk
>> @@ -126,6 +126,17 @@ endef
>>  check-$(gcc) = $(call cc-ver-check,CC,0x040100,"Xen requires at least 
>> gcc-4.1")
>>  $(eval $(check-y))
>>
>> +ld-ver = $(shell if [ $$((`$(1) --version | head -1 | sed 's/[^0-9]/ /g' | 
>> awk \
>> +           '{ printf "0x%02x%02x", $$1, $$2}'`)) -ge $$(($(2))) ]; \
>> +           then echo y; else echo n; fi ;)
>> +
>> +# binutils 2.18 implement build-id.
>> +ifeq ($(call ld-ver,$(LD),0x0212),n)
>> +build_id :=
>> +else
>> +build_id := --build-id=sha1
>> +endif
>
> Wouldn't it be better to probe the linker for recognizing the --build-id
> command line option, along the lines of $(cc-option)?

+ld-ver-build-id = $(shell $(1) --build-id 2>&1 | \
+                                       grep -q unrecognized && echo n
|| echo y)

-ish ?

>
> In any event the option should be added to LDFLAGS unless this
> conflicts with something else.

That had some interesting side-effect:

$ find . -name *.o | xargs readelf -n | more
File: ./arch/x86/built_in.o

Displaying notes found at file offset 0x00000040 with length 0x00000240:
  Owner                 Data size       Description
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: a114d1fdec2ace38448f141013f5a659122f2390
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: 4a913d3d1ece4d175fc0df0b36745b801f88bfab
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: ead89ba3aa9a8257cfc863966b7a9a725ecce133
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: 9b034a93573015c611d0900e949370d9f776bac1
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: 0e5fab6126ce69edd5720b96e2d5414618259c78
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: 49eca2138553b5e85ee45bb47c52aca394c31c31
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: f1cc2c8ae09fefe1440662efc44208a0b9ff8ddd
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: 29991f03f7a1aeeb59c8f83c0e7a349384a7262c
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: 3e2c4df9f60fdbd970bd1a35d03c7b68fd794385
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: 2c4f5cd9bcf553a022dace08b7741d85a4eb657f
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: 41c502289e5b28722ab5df6ae5bd7b99fb90c09e
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: f268afebdf211de6bb6d12e513520bba969130cc
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: b73b7296f6165d3dcacee36691d92ab1996d9908
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: ff8e080d8e01966cf8d893ce6cd258dd0d1c6124
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: dcc8964716f74bb710911d80faaae016820f72d9
  GNU                  0x00000014       NT_GNU_BUILD_ID (unique build
ID bitstring)
    Build ID: 649f4bb66df2fead426edda62d0c90ab088c5fd4


And during build:
ld: warning: Cannot create .note.gnu.build-id section, --build-id ignored.
ld: warning: Cannot create .note.gnu.build-id section, --build-id ignored.
ld: warning: Cannot create .note.gnu.build-id section, --build-id ignored.

With:
[konrad@char xen]$ readelf -n xen-syms  | grep Build | wc
     38     114    2090

I think we should skip on the LDFLAGS idea.

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