[Buildroot] [PATCH v2, 1/1] toolchain/toolchain-wrapper: fix gcc -v with relro

[Yann E. MORIN <yann.morin.1998@free.fr>]

Fabrice, All,

On 2020-12-24 11:18 +0100, Fabrice Fontaine spake thusly:
> rhash in version 1.4.0 with relro fails to build because gcc -v raises
> the following build failure:
> 
> /data/buildroot-test/instance-1/output-1/host/mips64el-buildroot-linux-gnu/sysroot/soft-float/el/usr/lib64/Scrt1.o: In function `__start':
> (.text+0x20): undefined reference to `main'
> collect2: error: ld returned 1 exit status
> Run result: 1
> 
> This build failure is raised because the toolchain-wrapper calls gcc with
> -Wl,-z,relro and as a result gcc wrongly assumes that some linking must
> be done.

Although I do undesrstand the problem, I am not sure this is a good
solution.

Indeed, it is perfectly legit to call gcc -v while doing an acutal
compile or link:

    $ echo 'main() { return 0; }' |gcc -v -Wl,-z,relro -o ess -x c -

Indeed, using -v is a good way to see the actual programs gcc calls in
the various steps, and has already helped me debug some difficult
issues...

So, I think we need to be a little bit smarter in how we detect whether
an actual link is attempted. It is however not trivial to come up with
such a heuristic.

But it might be simpler to "fix" rhash itself, with something like:

    diff -durN rhash-1.4.0.orig/configure rhash-1.4.0/configure
    --- rhash-1.4.0.orig/configure2020-07-14 21:35: 11.000000000 +0200
    +++ rhash-1.4.0/configure2020-12-25 18:07:15.52 9581029 +0100
    @@ -513,8 +513,13 @@
       CC_TMP="$CC"
       test -n "$OPT_CC" && OTHER_CC= || OTHER_CC="gcc cc"
       for CC in "$CC_TMP" $OTHER_CC; do
    +    cc_name_tmp=
         if run_cmd "$CC -v"; then
           cc_name_tmp=$($CC -v 2>&1 | tail -n 1 | cut -d ' ' -f 1)
    +    elif run_cmd "$CC --version"; then
    +      cc_name_tmp=$($CC --version 2>&1 | head -n 1 | cut -d ' ' -f 1)
    +    fi
    +    if test "${cc_name_tmp}"; then
           if test "$cc_name_tmp" = "gcc"; then
             cc_name=$cc_name_tmp
             start_check "$CC version"

This should also be hopefully accpetable upstream (too bad they do not
want to switch a common, well-known buildsystem, and that the cmake
suppot has languished without any comment for more than a year now...)

Regards,
Yann E. MORIN.

> Fixes:
>  - http://autobuild.buildroot.org/results/8605c16cc28316954ce8b9dcc266974390c5da20
> 
> Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
> Tested-by: Peter Seiderer <ps.report@gmx.net>
> ---
> Changes v1 -> v2 (after review of Peter Seiderer):
>  - Fix typos in commit log and update comment in source code
> 
>  toolchain/toolchain-wrapper.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/toolchain/toolchain-wrapper.c b/toolchain/toolchain-wrapper.c
> index 0fb6064b1c..2a7dd61729 100644
> --- a/toolchain/toolchain-wrapper.c
> +++ b/toolchain/toolchain-wrapper.c
> @@ -453,10 +453,11 @@ int main(int argc, char **argv)
>  			*cur++ = "-pie";
>  	}
>  #endif
> -	/* Are we building the Linux Kernel or U-Boot? */
> +	/* Are we building the Linux Kernel or U-Boot or displaying the programs invoked by the compiler? */
>  	for (i = 1; i < argc; i++) {
>  		if (!strcmp(argv[i], "-D__KERNEL__") ||
> -		    !strcmp(argv[i], "-D__UBOOT__"))
> +		    !strcmp(argv[i], "-D__UBOOT__") ||
> +		    !strcmp(argv[i], "-v"))
>  			break;
>  	}
>  	if (i == argc) {
> -- 
> 2.29.2
> 
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