linux-kernel - Re: [PATCH 1/3] scripts/sorttable: Change section type of orc_lookup to SHT

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Date:   Tue, 4 Aug 2020 09:40:40 +0800
From:   changhuaixin <changhuaixin@...ux.alibaba.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     changhuaixin <changhuaixin@...ux.alibaba.com>, bp@...en8.de,
        hpa@...or.com, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, luto@...capital.net,
        michal.lkml@...kovi.net, mingo@...hat.com,
        Peter Zijlstra <peterz@...radead.org>, tglx@...utronix.de,
        x86@...nel.org, yamada.masahiro@...ionext.com, jpoimboe@...hat.com
Subject: Re: [PATCH 1/3] scripts/sorttable: Change section type of orc_lookup
 to SHT_PROGBITS

Hi, Ingo

Another way to write SHT_PROGBITS is using elf_create_section to write orc_lookup table headers, when orc_unwind_ip table and orc_unwind table are written. Is this a better solution?

diff --git a/tools/objtool/orc_gen.c b/tools/objtool/orc_gen.c
index 3f98dcfbc177..860d4dcec8e6 100644
--- a/tools/objtool/orc_gen.c
+++ b/tools/objtool/orc_gen.c
@@ -183,6 +183,10 @@ int create_orc_sections(struct objtool_file *file)
        u_sec = elf_create_section(file->elf, ".orc_unwind",
                                   sizeof(struct orc_entry), idx);

+       /* make flags of section orc_lookup right */
+       if (!elf_create_section(file->elf, ".orc_lookup", sizeof(int), 0))
+               return -1;
+
        /* populate sections */
        idx = 0;
        for_each_sec(file, sec) {

Thanks,
Huaixin

> On Jul 23, 2020, at 11:46 AM, Huaixin Chang <changhuaixin@...ux.alibaba.com> wrote:
> 
> In order to edit orc_lookup table via sorttable, type of section
> orc_lookup needs to be SHT_PROGBITS instead of SHT_NOBITS.
> 
> Linker script doesn't seem to allow manual specification of the section
> type, so just write a byte into the section instead.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Signed-off-by: Huaixin Chang <changhuaixin@...ux.alibaba.com>
> Signed-off-by: Shile Zhang <shile.zhang@...ux.alibaba.com>
> ---
> include/asm-generic/vmlinux.lds.h | 2 ++
> 1 file changed, 2 insertions(+)
> 
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index db600ef218d7..49f4f5bc6165 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -826,6 +826,8 @@
> 		. += (((SIZEOF(.text) + LOOKUP_BLOCK_SIZE - 1) /	\
> 			LOOKUP_BLOCK_SIZE) + 1) * 4;			\
> 		orc_lookup_end = .;					\
> +		/* HACK: force SHT_PROGBITS so sorttable can edit: */	\
> +		BYTE(1);						\
> 	}
> #else
> #define ORC_UNWIND_TABLE
> -- 
> 2.14.4.44.g2045bb6