linux-kernel - Re: [PATCH v2 16/16] objtool/powerpc: Add --mcount specific implementation

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Message-ID: <5da86617-53f1-d899-336a-53fe691e76ae@csgroup.eu>
Date:   Wed, 31 Aug 2022 12:50:07 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Sathvika Vasireddy <sv@...ux.ibm.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
CC:     "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "aik@...abs.ru" <aik@...abs.ru>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "mbenes@...e.cz" <mbenes@...e.cz>,
        "npiggin@...il.com" <npiggin@...il.com>,
        "chenzhongjin@...wei.com" <chenzhongjin@...wei.com>,
        "naveen.n.rao@...ux.vnet.ibm.com" <naveen.n.rao@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 16/16] objtool/powerpc: Add --mcount specific
 implementation



Le 29/08/2022 à 07:52, Sathvika Vasireddy a écrit :
> This patch enables objtool --mcount on powerpc, and
> adds implementation specific to powerpc.
> 
> Signed-off-by: Sathvika Vasireddy <sv@...ux.ibm.com>
> ---
>   arch/powerpc/Kconfig                          |  1 +
>   tools/objtool/arch/powerpc/decode.c           | 22 +++++++++++++++++++
>   tools/objtool/arch/powerpc/include/arch/elf.h |  2 ++
>   3 files changed, 25 insertions(+)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index dc05cd23c233..6be2e68fa9eb 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -238,6 +238,7 @@ config PPC
>   	select HAVE_NMI				if PERF_EVENTS || (PPC64 && PPC_BOOK3S)
>   	select HAVE_OPTPROBES
>   	select HAVE_OBJTOOL			if PPC32 || MPROFILE_KERNEL
> +	select HAVE_OBJTOOL_MCOUNT		if HAVE_OBJTOOL
>   	select HAVE_PERF_EVENTS
>   	select HAVE_PERF_EVENTS_NMI		if PPC64
>   	select HAVE_PERF_REGS
> diff --git a/tools/objtool/arch/powerpc/decode.c b/tools/objtool/arch/powerpc/decode.c
> index 8b6a14680da7..b71c265ed503 100644
> --- a/tools/objtool/arch/powerpc/decode.c
> +++ b/tools/objtool/arch/powerpc/decode.c
> @@ -9,6 +9,14 @@
>   #include <objtool/builtin.h>
>   #include <objtool/endianness.h>
>   
> +bool arch_ftrace_match(char *name)
> +{
> +	if (!strcmp(name, "_mcount"))
> +		return true;
> +
> +	return false;
> +}
> +
>   unsigned long arch_dest_reloc_offset(int addend)
>   {
>   	return addend;
> @@ -41,12 +49,26 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
>   			    struct list_head *ops_list)
>   {
>   	u32 insn;
> +	unsigned int opcode;
>   
>   	*immediate = 0;
>   	insn = bswap_if_needed(file->elf, *(u32 *)(sec->data->d_buf + offset));
>   	*len = 4;
>   	*type = INSN_OTHER;
>   
> +	opcode = insn >> 26;
> +
> +	switch (opcode) {
> +	case 18: /* bl */

case 18 is more than 'bl', it includes also 'b'.
In both cases, the calculation of *immediate is the same.

It would therefore be more correct to perform the calculation and setup 
of *immediate outside the 'if ((insn & 3) == 1)', that would avoid 
unnecessary churn the day we add support for branches without link.

> +		if ((insn & 3) == 1) {
> +			*type = INSN_CALL;
> +			*immediate = insn & 0x3fffffc;
> +			if (*immediate & 0x2000000)
> +				*immediate -= 0x4000000;
> +		}
> +		break;
> +	}
> +
>   	return 0;
>   }
>   
> diff --git a/tools/objtool/arch/powerpc/include/arch/elf.h b/tools/objtool/arch/powerpc/include/arch/elf.h
> index 3c8ebb7d2a6b..73f9ae172fe5 100644
> --- a/tools/objtool/arch/powerpc/include/arch/elf.h
> +++ b/tools/objtool/arch/powerpc/include/arch/elf.h
> @@ -4,5 +4,7 @@
>   #define _OBJTOOL_ARCH_ELF
>   
>   #define R_NONE R_PPC_NONE
> +#define R_ABS64 R_PPC64_ADDR64
> +#define R_ABS32 R_PPC_ADDR32
>   
>   #endif /* _OBJTOOL_ARCH_ELF */