linux-kernel - Re: [PATCH v2 01/13] livepatch: Fix build failure on 32 bits processors

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Message-ID: <YdShcXQwOaQnylo6@redhat.com>
Date:   Tue, 4 Jan 2022 14:35:13 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>
Subject: Re: [PATCH v2 01/13] livepatch: Fix build failure on 32 bits
 processors

On Mon, Dec 20, 2021 at 04:38:02PM +0000, Christophe Leroy wrote:
> Trying to build livepatch on powerpc/32 results in:
> 
> 	kernel/livepatch/core.c: In function 'klp_resolve_symbols':
> 	kernel/livepatch/core.c:221:23: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> 	  221 |                 sym = (Elf64_Sym *)sechdrs[symndx].sh_addr + ELF_R_SYM(relas[i].r_info);
> 	      |                       ^
> 	kernel/livepatch/core.c:221:21: error: assignment to 'Elf32_Sym *' {aka 'struct elf32_sym *'} from incompatible pointer type 'Elf64_Sym *' {aka 'struct elf64_sym *'} [-Werror=incompatible-pointer-types]
> 	  221 |                 sym = (Elf64_Sym *)sechdrs[symndx].sh_addr + ELF_R_SYM(relas[i].r_info);
> 	      |                     ^
> 	kernel/livepatch/core.c: In function 'klp_apply_section_relocs':
> 	kernel/livepatch/core.c:312:35: error: passing argument 1 of 'klp_resolve_symbols' from incompatible pointer type [-Werror=incompatible-pointer-types]
> 	  312 |         ret = klp_resolve_symbols(sechdrs, strtab, symndx, sec, sec_objname);
> 	      |                                   ^~~~~~~
> 	      |                                   |
> 	      |                                   Elf32_Shdr * {aka struct elf32_shdr *}
> 	kernel/livepatch/core.c:193:44: note: expected 'Elf64_Shdr *' {aka 'struct elf64_shdr *'} but argument is of type 'Elf32_Shdr *' {aka 'struct elf32_shdr *'}
> 	  193 | static int klp_resolve_symbols(Elf64_Shdr *sechdrs, const char *strtab,
> 	      |                                ~~~~~~~~~~~~^~~~~~~
> 
> Fix it by using the right types instead of forcing 64 bits types.
> 
> Fixes: 7c8e2bdd5f0d ("livepatch: Apply vmlinux-specific KLP relocations early")
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> Acked-by: Petr Mladek <pmladek@...e.com>
> ---
>  kernel/livepatch/core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 335d988bd811..c0789383807b 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -190,7 +190,7 @@ static int klp_find_object_symbol(const char *objname, const char *name,
>  	return -EINVAL;
>  }
>  
> -static int klp_resolve_symbols(Elf64_Shdr *sechdrs, const char *strtab,
> +static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
>  			       unsigned int symndx, Elf_Shdr *relasec,
>  			       const char *sec_objname)
>  {
> @@ -218,7 +218,7 @@ static int klp_resolve_symbols(Elf64_Shdr *sechdrs, const char *strtab,
>  	relas = (Elf_Rela *) relasec->sh_addr;
>  	/* For each rela in this klp relocation section */
>  	for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) {
> -		sym = (Elf64_Sym *)sechdrs[symndx].sh_addr + ELF_R_SYM(relas[i].r_info);
> +		sym = (Elf_Sym *)sechdrs[symndx].sh_addr + ELF_R_SYM(relas[i].r_info);
>  		if (sym->st_shndx != SHN_LIVEPATCH) {
>  			pr_err("symbol %s is not marked as a livepatch symbol\n",
>  			       strtab + sym->st_name);
> -- 
> 2.33.1
> 

Thanks for finding and fixing, lgtm.

Acked-by: Joe Lawrence <joe.lawrence@...hat.com>

-- Joe