linux-kernel - Re: [PATCH] nds32/ftrace: Fix Error: invalid operands (*UND* and *UND* sections) for `^'

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Date:   Fri, 15 Oct 2021 08:54:35 +0800
From:   Greentime Hu <green.hu@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Nick Hu <nickhu@...estech.com>,
        Vincent Chen <deanbo422@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>, Zong Li <zong@...estech.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        kernel test robot <lkp@...el.com>,
        Alan Kao <alankao@...estech.com>, kclin@...estech.com
Subject: Re: [PATCH] nds32/ftrace: Fix Error: invalid operands (*UND* and
 *UND* sections) for `^'

Steven Rostedt <rostedt@...dmis.org> 於 2021年10月15日 週五 上午2:35寫道：
>
> [ Resending with "PATCH" in subject ]
>
> I received a build failure for a new patch I'm working on the nds32
> architecture, and when I went to test it, I couldn't get to my build error,
> because it failed to build with a bunch of:
>
>   Error: invalid operands (*UND* and *UND* sections) for `^'
>
> issues with various files. Those files were temporary asm files that looked
> like:  kernel/.tmp_mc_fork.s
>
> I decided to look deeper, and found that the "mc" portion of that name
> stood for "mcount", and was created by the recordmcount.pl script. One that
> I wrote over a decade ago. Once I knew the source of the problem, I was
> able to investigate it further.
>
> The way the recordmcount.pl script works (BTW, there's a C version that
> simply modifies the ELF object) is by doing an "objdump" on the object
> file. Looks for all the calls to "mcount", and creates an offset of those
> locations from some global variable it can use (usually a global function
> name, found with <.*>:). Creates a asm file that is a table of references
> to these locations, using the found variable/function. Compiles it and
> links it back into the original object file. This asm file is called
> ".tmp_mc_<object_base_name>.s".
>
> The problem here is that the objdump produced by the nds32 object file,
> contains things that look like:
>
>  0000159a <.L3^B1>:
>     159a:       c6 00           beqz38 $r6, 159a <.L3^B1>
>                         159a: R_NDS32_9_PCREL_RELA      .text+0x159e
>     159c:       84 d2           movi55 $r6, #-14
>     159e:       80 06           mov55 $r0, $r6
>     15a0:       ec 3c           addi10.sp #0x3c
>
>
> Where ".L3^B1 is somehow selected as the "global" variable to index off of.
>
> Then the assembly file that holds the mcount locations looks like this:
>
>         .section __mcount_loc,"a",@progbits
>         .align 2
>         .long .L3^B1 + -5522
>         .long .L3^B1 + -5384
>         .long .L3^B1 + -5270
>         .long .L3^B1 + -5098
>         .long .L3^B1 + -4970
>         .long .L3^B1 + -4758
>         .long .L3^B1 + -4122
>         [...]
>
> And when it is compiled back to an object to link to the original object,
> the compile fails on the "^" symbol.
>
> Simple solution for now, is to have the perl script ignore using function
> symbols that have an "^" in the name.
>
> Fixes: fbf58a52ac088 ("nds32/ftrace: Add RECORD_MCOUNT support")
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
> diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
> index 8f6b13ae46bf..7d631aaa0ae1 100755
> --- a/scripts/recordmcount.pl
> +++ b/scripts/recordmcount.pl
> @@ -189,7 +189,7 @@ if ($arch =~ /(x86(_64)?)|(i386)/) {
>  $local_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\S+)";
>  $weak_regex = "^[0-9a-fA-F]+\\s+([wW])\\s+(\\S+)";
>  $section_regex = "Disassembly of section\\s+(\\S+):";
> -$function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:";
> +$function_regex = "^([0-9a-fA-F]+)\\s+<([^^]*?)>:";
>  $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s(mcount|__fentry__)\$";
>  $section_type = '@...gbits';
>  $mcount_adjust = 0;
loop in Alan and KC