linux-kernel - Re: [PATCH 7/7] DWARF: add the config option

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Message-ID: <b877fd60-c9a4-cd2e-919a-68172f31285f@suse.cz>
Date:   Fri, 26 May 2017 13:29:01 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        live-patching@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 7/7] DWARF: add the config option

On 05/26/2017, 08:54 AM, Jiri Slaby wrote:
> On 05/19/2017, 11:35 PM, Josh Poimboeuf wrote:
>>   https://github.com/jpoimboe/linux/blob/undwarf/arch/x86/kernel/unwind_undwarf.c
> 
> JFYI, it crashes in sha1_transform_avx due to crypto changes. You
> perhaps missed that this beast uses ebp (not rbp) register for
> computations. I had to do:
> 
> --- a/arch/x86/crypto/sha1_ssse3_asm.S
> +++ b/arch/x86/crypto/sha1_ssse3_asm.S
> @@ -37,7 +37,7 @@
>  #define REG_A  %ecx
>  #define REG_B  %esi
>  #define REG_C  %edi
> -#define REG_D  %ebp
> +#define REG_D  %r12d
>  #define REG_E  %edx
> 
>  #define REG_T1 %eax
> @@ -74,6 +74,7 @@
>         SYM_FUNC_START(\name)
> 
>         push    %rbx
> +       push    %r12
>         push    %rbp
> 
>         mov     %rsp, %rbp
> @@ -99,6 +100,7 @@
>         rep stosq
> 
>         leaveq                          # deallocate workspace
> +       pop     %r12
>         pop     %rbx
>         ret
> 
> 
> I am afraid there are more of these, e.g. in aesni-intel_asm.S.

aesni-intel_asm.S is OK -- only untouched x86_32 part uses ebp.

But sha1_avx2_x86_64_asm.S is not. They use *all* usable registers
including ebp in the computations hidden behind the
SHA1_PIPELINED_MAIN_BODY macro. The only work around I can see is to
push rbp/pop rbp around the computation as it used to do with rbx:

--- a/arch/x86/crypto/sha1_avx2_x86_64_asm.S
+++ b/arch/x86/crypto/sha1_avx2_x86_64_asm.S
@@ -636,6 +636,7 @@ _loop3:
        /* Align stack */
        mov     %rsp, %rbp
        and     $~(0x20-1), %rsp
+       push    %rbp
        sub     $RESERVE_STACK, %rsp

        avx2_zeroupper
@@ -661,6 +662,7 @@ _loop3:
        avx2_zeroupper

        add     $RESERVE_STACK, %rsp
+       pop     %rbp

        leaveq
        pop     %r15

regards,
-- 
js
suse labs