CONFIG_STACK_VALIDATION=y HOSTCC=clang

[nickdesaulniers]

It was reported that the following error was encountered:

$ make HOSTCC=clang CC=clang  -j32 ARCH=x86_64 prepare
...
scripts/kconfig/conf  --silentoldconfig Kconfig
Makefile:965: *** "Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel".  Stop.

But the latest libelf-dev has been installed with version 0.170-0.4.

Reported-by: Hao, Shun shun.hao@intel.com

[nickdesaulniers]

So the Makefile has the code:

 960 ifdef CONFIG_STACK_VALIDATION                                                   
 961   has_libelf := $(call try-run,\                                                
 962     echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -,1,0)              
 963   ifeq ($(has_libelf),1)                                                        
 964     objtool_target := tools/objtool FORCE                                       
 965   else                                                                          
 966     ifdef CONFIG_UNWINDER_ORC                                                   
 967       $(error "Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel")
...

So it looks like it's running:

$(echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -,1,0)

I think this is wrong because:

➜  kernel-all git:(master) ✗ HOSTCC=/android1/llvm/build/bin/clang-7.0; $(echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -,1,0)
zsh: command not found: HOSTCC
zsh: command not found: -xc

it seems that HOSTCC is not defined for the subshell?

HOSTCC=/android1/llvm/build/bin/clang-7.0; $(echo "int main() {}" | $HOSTCC -xc -o /dev/null -lelf -)

seems to work.

[tpimh]

You are right, creating subshell here is a mistake. Probably the original author meant ${HOSTCC}, not $(HOSTCC). But this is not the only mistake here.
If your .config has CONFIG_STACK_VALIDATION=y and # CONFIG_UNWINDER_ORC is not set. It will still print an error as if CONFIG_UNWINDER_ORC is defined (but actually it should just print a warning and set SKIP_STACK_VALIDATION variable). Do you have CONFIG_UNWINDER_ORC set in your .config?
Btw, last time I tried building libelf with clang, it was a pain (had to completely rewrite some gcc-specific parts).

[nickdesaulniers]

I'm no longer able to reproduce. I wonder if the CONFIG_STACK_VALIDATION check is no longer running at all?

[tpimh]

Which version are you building? I'm on 5211da9 and it is still there. The stranger thing is that my .config is:

CONFIG_STACK_VALIDATION=y
# CONFIG_UNWINDER_ORC is not set

And I'm still given an error, not a warning. Relevant part of the Makefile:

ifdef CONFIG_STACK_VALIDATION                         
  has_libelf := $(call try-run,\      
                echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -,1,0)
  ifeq ($(has_libelf),1)                                    
    objtool_target := tools/objtool FORCE
  else                                                            
    ifdef CONFIG_UNWINDER_ORC
      $(error "Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel")
    else
      $(warning "Cannot use CONFIG_STACK_VALIDATION=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel")
    endif                                                           
    SKIP_STACK_VALIDATION := 1                                
    export SKIP_STACK_VALIDATION        
  endif
endif                                   

[nathanchance]

This should be fixed as of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ef7cfd00b2caf6edeb7f169682b64be2d0a798cf.

@tpimh can you test and close this issue if that is the case?

[tpimh]

Yes, now it behaves how it should. Tested with CONFIG_STACK_VALIDATION and CONFIG_UNWINDER_ORC (errors and stops), with CONFIG_STACK_VALIDATION and no CONFIG_UNWINDER_ORC (warns and continues) and without both CONFIG_STACK_VALIDATION and CONFIG_UNWINDER_ORC (no warning). These are expected behaviors.

[nickdesaulniers]

Thanks @masahir0y !