Re: [PATCH 3/3] livepatch: correctly handle altinstruction sections

From: Jan Beulich <jbeulich@suse.com>
To: Roger Pau Monne <roger.pau@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Ross Lagerwall <ross.lagerwall@citrix.com>,
	doebel@amazon.de, xen-devel@lists.xenproject.org
Subject: Re: [PATCH 3/3] livepatch: correctly handle altinstruction sections
Date: Fri, 11 Mar 2022 08:35:18 +0100	[thread overview]
Message-ID: <2e2781eb-2c62-1c93-ef8e-75054a213fb8@suse.com> (raw)
In-Reply-To: <20220310150834.98815-4-roger.pau@citrix.com>

On 10.03.2022 16:08, Roger Pau Monne wrote:
> --- a/common.c
> +++ b/common.c
> @@ -249,19 +249,22 @@ int is_text_section(struct section *sec)
>  		(sec->sh.sh_flags & SHF_EXECINSTR));
>  }
>  
> +#define SEC_MATCH(n) !strncmp(sec->name, n, strlen(n) - 1)
>  int is_rodata_section(struct section *sec)
>  {
>  	return sec->sh.sh_type == SHT_PROGBITS &&
>  	       !(sec->sh.sh_flags & (SHF_EXECINSTR | SHF_WRITE)) &&
> -	       !strncmp(sec->name, ".rodata", 7);
> +	       (SEC_MATCH(".rodata") || SEC_MATCH(".data.ro_after_init"));
>  }
>  
>  int is_init_section(struct section *sec)
>  {
>  	return sec->sh.sh_type == SHT_PROGBITS &&
>  	       (sec->sh.sh_flags & SHF_ALLOC) &&
> -	       !strncmp(sec->name, ".init", 5);
> +	       (SEC_MATCH(".init") || SEC_MATCH(".text.startup") ||
> +	        SEC_MATCH(".altinstr") || SEC_MATCH(".ctors"));

Having dealt with this recently - what about .init_array? Modern gcc
prefers that over .ctors. Of course the question is whether either
really needs dealing with here - these sections, to my knowledge,
appear only with gcov support enabled. Not sure that's a case where
livepatching is actually expected to be used.

Jan