Re: [PATCH 5.10 00/59] 5.10.223-rc1 review

[Jari Ruusu]

Some older systems still compile kernels with old gcc version.

$ grep -B3 "^GNU C" linux-5.10.223-rc1/Documentation/Changes 
====================== ===============  ========================================
        Program        Minimal version       Command to check the version
====================== ===============  ========================================
GNU C                  4.9              gcc --version

These warnings and errors show up when compiling with gcc 4.9.2

  UPD     include/config/kernel.release
  UPD     include/generated/uapi/linux/version.h
  UPD     include/generated/utsrelease.h
  CC      scripts/mod/empty.o
In file included from ././include/linux/compiler_types.h:65:0,
                 from <command-line>:0:
./include/linux/compiler_attributes.h:29:29: warning: "__GCC4_has_attribute___uninitialized__" is not defined [-Wundef]
 # define __has_attribute(x) __GCC4_has_attribute_##x
                             ^
./include/linux/compiler_attributes.h:278:5: note: in expansion of macro '__has_attribute'
 #if __has_attribute(__uninitialized__)
     ^
[SNIP]
  AR      arch/x86/events/built-in.a
  CC      arch/x86/kvm/../../../virt/kvm/kvm_main.o
In file included from ././include/linux/compiler_types.h:65:0,
                 from <command-line>:0:
./include/linux/compiler_attributes.h:29:29: error: "__GCC4_has_attribute___uninitialized__" is not defined [-Werror=undef]
 # define __has_attribute(x) __GCC4_has_attribute_##x
                             ^
./include/linux/compiler_attributes.h:278:5: note: in expansion of macro '__has_attribute'
 #if __has_attribute(__uninitialized__)
     ^
cc1: all warnings being treated as errors
make[2]: *** [scripts/Makefile.build:286: arch/x86/kvm/../../../virt/kvm/kvm_main.o] Error 1
make[1]: *** [scripts/Makefile.build:503: arch/x86/kvm] Error 2
make: *** [Makefile:1832: arch/x86] Error 2

Following patch fixes this. Upstream won't need this because
newer kernels are not compilable with gcc 4.9

--- ./include/linux/compiler_attributes.h.OLD
+++ ./include/linux/compiler_attributes.h
@@ -37,6 +37,7 @@
 # define __GCC4_has_attribute___nonstring__           0
 # define __GCC4_has_attribute___no_sanitize_address__ (__GNUC_MINOR__ >= 8)
 # define __GCC4_has_attribute___no_sanitize_undefined__ (__GNUC_MINOR__ >= 9)
+# define __GCC4_has_attribute___uninitialized__       0
 # define __GCC4_has_attribute___fallthrough__         0
 # define __GCC4_has_attribute___warning__             1
 #endif

Fixes: upstream fd7eea27a3ae "Compiler Attributes: Add __uninitialized macro"
Signed-off-by: Jari Ruusu <jariruusu@xxxxxxxxxxxxxx>

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Jari Ruusu  4096R/8132F189 12D6 4C3A DCDA 0AA4 27BD  ACDF F073 3C80 8132 F189