linux-kernel - Re: [PATCH v3 3/4] LoongArch: Remove -fplt and -Wa,-mla-* from CFLAGS

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <54026014a1894a3f1eb0056dbc61a8ce31f4d2da.camel@xry111.site>
Date:   Fri, 29 Jul 2022 10:50:59 +0800
From:   Xi Ruoyao <xry111@...111.site>
To:     loongarch@...ts.linux.dev, Huacai Chen <chenhuacai@...nel.org>
Cc:     linux-kernel@...r.kernel.org, WANG Xuerui <kernel@...0n.name>,
        Youling Tang <tangyouling@...ngson.cn>,
        Jinyang He <hejinyang@...ngson.cn>
Subject: Re: [PATCH v3 3/4] LoongArch: Remove -fplt and -Wa,-mla-* from
 CFLAGS

On Fri, 2022-07-29 at 10:09 +0800, Xi Ruoyao wrote:
> -fplt is the default of all supported compilers (GCC, and maybe Clang in
> the future), so it needs not to be explicitly specified.
> 
> -Wa,-mla-* options were used to prevent the assembler from generating
> GOT accesses for "la.local" and "la.global" macros.  But GCC >= 13 will
> generate GOT access explicitly without use of these macros

Will add "by default with an assembler supporting explicit relocations,
and it's not recommended to override the default" here in V4.

> options are ineffective for symbol addressing in C code with GCC >= 13.
> Now we can handle GOT and GOT-based relocations properly, so we can
> remove these options and use GOT access for both GCC 12 and 13
> (or newer).
> 
> GAS <= 2.39 does not support "la.got [reg], [sym] + [offset]" with a
> non-zero offset.  So in the assembly code we explicitly use "la.pcrel"
> instead of "la" (now defaulted to "la.got") where a PC-relative
> addressing is suitable, in order to work around this limitation and keep
> the compatibility with old toolchains.
> 
> Signed-off-by: Xi Ruoyao <xry111@...111.site>
> ---
>  arch/loongarch/Makefile      |  4 ----
>  arch/loongarch/kernel/head.S | 10 +++++-----
>  2 files changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index 039dcc4fe1f3..800349ea9310 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -40,10 +40,6 @@ endif
>  
>  cflags-y                       += -G0 -pipe -msoft-float
>  LDFLAGS_vmlinux                        += -G0 -static -n -nostdlib
> -KBUILD_AFLAGS_KERNEL           += -Wa,-mla-global-with-pcrel
> -KBUILD_CFLAGS_KERNEL           += -Wa,-mla-global-with-pcrel
> -KBUILD_AFLAGS_MODULE           += -Wa,-mla-global-with-abs
> -KBUILD_CFLAGS_MODULE           += -fplt -Wa,-mla-global-with-abs,-mla-local-with-abs
>  
>  cflags-y += -ffreestanding
>  cflags-y += $(call cc-option, -mno-check-zero-division)
> diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
> index 74ea7bf6c8d6..193329ed6e8c 100644
> --- a/arch/loongarch/kernel/head.S
> +++ b/arch/loongarch/kernel/head.S
> @@ -60,17 +60,17 @@ SYM_CODE_START(kernel_entry)                        # kernel entry point
>         la.abs          t0, 0f
>         jirl            zero, t0, 0
>  0:
> -       la              t0, __bss_start         # clear .bss
> +       la.pcrel        t0, __bss_start         # clear .bss
>         st.d            zero, t0, 0
> -       la              t1, __bss_stop - LONGSIZE
> +       la.pcrel        t1, __bss_stop - LONGSIZE
>  1:
>         addi.d          t0, t0, LONGSIZE
>         st.d            zero, t0, 0
>         bne             t0, t1, 1b
>  
> -       la              t0, fw_arg0
> +       la.pcrel        t0, fw_arg0
>         st.d            a0, t0, 0               # firmware arguments
> -       la              t0, fw_arg1
> +       la.pcrel        t0, fw_arg1
>         st.d            a1, t0, 0
>  
>         /* KSave3 used for percpu base, initialized as 0 */
> @@ -78,7 +78,7 @@ SYM_CODE_START(kernel_entry)                  # kernel entry point
>         /* GPR21 used for percpu base (runtime), initialized as 0 */
>         or              u0, zero, zero
>  
> -       la              tp, init_thread_union
> +       la.pcrel        tp, init_thread_union
>         /* Set the SP after an empty pt_regs.  */
>         PTR_LI          sp, (_THREAD_SIZE - 32 - PT_SIZE)
>         PTR_ADD         sp, sp, tp

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University