linux-kernel - Re: [PATCH 1/3] scripts/recordmcount.pl: Fix RISC-V regex for clang

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Date:   Thu, 25 Mar 2021 16:36:40 -0700
From:   Fangrui Song <maskray@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com, stable@...r.kernel.org
Subject: Re: [PATCH 1/3] scripts/recordmcount.pl: Fix RISC-V regex for clang

On 2021-03-25, Nathan Chancellor wrote:
>Clang can generate R_RISCV_CALL_PLT relocations to _mcount:
>
>$ llvm-objdump -dr build/riscv/init/main.o | rg mcount
>                000000000000000e:  R_RISCV_CALL_PLT     _mcount
>                000000000000004e:  R_RISCV_CALL_PLT     _mcount
>
>After this, the __start_mcount_loc section is properly generated and
>function tracing still works.
>

R_RISCV_CALL_PLT can replace R_RISCV_CALL in all use cases.
R_RISCV_CALL can/may be deprecated:
https://github.com/ClangBuiltLinux/linux/issues/1331#issuecomment-802468296

Reviewed-by: Fangrui Song <maskray@...gle.com>


>Cc: stable@...r.kernel.org
>Link: https://github.com/ClangBuiltLinux/linux/issues/1331
>Signed-off-by: Nathan Chancellor <nathan@...nel.org>
>---
> scripts/recordmcount.pl | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
>index 867860ea57da..a36df04cfa09 100755
>--- a/scripts/recordmcount.pl
>+++ b/scripts/recordmcount.pl
>@@ -392,7 +392,7 @@ if ($arch eq "x86_64") {
>     $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
> } elsif ($arch eq "riscv") {
>     $function_regex = "^([0-9a-fA-F]+)\\s+<([^.0-9][0-9a-zA-Z_\\.]+)>:";
>-    $mcount_regex = "^\\s*([0-9a-fA-F]+):\\sR_RISCV_CALL\\s_mcount\$";
>+    $mcount_regex = "^\\s*([0-9a-fA-F]+):\\sR_RISCV_CALL(_PLT)?\\s_mcount\$";
>     $type = ".quad";
>     $alignment = 2;
> } elsif ($arch eq "nds32") {
>-- 
>2.31.0
>
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