[Intel-gfx] [PATCH 3/3] [RFC] Revert "drm/i915: use variadic macros and arrays to choose port/pipe based registers"

[Arnd Bergmann]

On Mon, Mar 20, 2017 at 11:08 AM, Jani Nikula
<jani.nikula at linux.intel.com> wrote:
> On Mon, 20 Mar 2017, Arnd Bergmann <arnd at arndb.de> wrote:
>> The varargs macro trick in _PIPE3/_PHY3/_PORT3 was meant as an optimization
>> to shrink the i915 kernel module by around 1000 bytes.
>
> To be clear, it was not at all intended to be an optimization, nothing
> of the sort. The intention was to make it easier and less error prone to
> add more parameters to said macros. The text size shring was just a
> bonus.
>
>> However, the
>> downside is a size regression with CONFIG_KASAN, as I found from stack size
>> warnings with gcc-7.0.1:
>
> In his review of the original change, Chris provided this comparison
> https://godbolt.org/g/YCK1od
>
> How does CONFIG_KASAN change this? Would be nice to see how the
> generated code blows up.
>
I don't know how to generate a URL for it, but after adding this to the
command line for gcc-7,

-fsanitize=kernel-address -fasan-shadow-offset=0xdfff900000000000
--param asan-stack=1 --param asan-globals=1 --param
asan-instrumentation-with-call-threshold=10000
-fsanitize-address-use-after-scope

the code turned from really nice into the log series of checks below.
Without  -fsanitize-address-use-after-scope (which didn't exist before gcc-7),
it's less bad but still exceeds the (arbitrary) 1536 byte limit.

     Arnd

.LC0:
        .string "2 32 4 1 i 96 24 9 <unknown> "
main:
.LASANPC0:
        pushq   %r12
        pushq   %rbp
        movabsq $-2305966154516004864, %rdx
        pushq   %rbx
        subq    $160, %rsp
        movq    %rsp, %rbp
        leaq    96(%rsp), %rbx
        movq    $1102416563, (%rsp)
        shrq    $3, %rbp
        movq    $.LC0, 8(%rsp)
        movq    $.LASANPC0, 16(%rsp)
        leaq    0(%rbp,%rdx), %rax
        movl    $-235802127, (%rax)
        movl    $-218959356, 4(%rax)
        movl    $-218959118, 8(%rax)
        movl    $-234881024, 12(%rax)
        movl    $-202116109, 16(%rax)
        movq    %rbx, %rax
        movl    $1, 32(%rsp)
        shrq    $3, %rax
        movzbl  (%rax,%rdx), %eax
        testb   %al, %al
        je      .L2
        cmpb    $3, %al
        jle     .L53
.L2:
        leaq    4(%rbx), %rdi
        movabsq $-2305966154516004864, %rax
        movl    $0, 96(%rsp)
        movq    %rdi, %rdx
        shrq    $3, %rdx
        movzbl  (%rdx,%rax), %edx
        movq    %rdi, %rax
        andl    $7, %eax
        addl    $3, %eax
        cmpb    %dl, %al
        jl      .L3
        testb   %dl, %dl
        jne     .L54
.L3:
        leaq    8(%rbx), %rdi
        movabsq $-2305966154516004864, %rax
        movl    $1, 100(%rsp)
        movq    %rdi, %rdx
        shrq    $3, %rdx
        movzbl  (%rdx,%rax), %eax
        testb   %al, %al
        je      .L4
        cmpb    $3, %al
        jle     .L55
.L4:
        leaq    12(%rbx), %rdi
        movabsq $-2305966154516004864, %rax
        movl    $2, 104(%rsp)
        movq    %rdi, %rdx
        shrq    $3, %rdx
        movzbl  (%rdx,%rax), %edx
        movq    %rdi, %rax
        andl    $7, %eax
        addl    $3, %eax
        cmpb    %dl, %al
        jl      .L5
        testb   %dl, %dl
        jne     .L56
.L5:
        leaq    16(%rbx), %rdi
        movabsq $-2305966154516004864, %rax
        movl    $3, 108(%rsp)
        movq    %rdi, %rdx
        shrq    $3, %rdx
        movzbl  (%rdx,%rax), %eax
        testb   %al, %al
        je      .L6
        cmpb    $3, %al
        jle     .L57
.L6:
        leaq    20(%rbx), %rdi
        movabsq $-2305966154516004864, %rax
        movl    $4, 112(%rsp)
        movq    %rdi, %rdx
        shrq    $3, %rdx
        movzbl  (%rdx,%rax), %edx
        movq    %rdi, %rax
        andl    $7, %eax
        addl    $3, %eax
        cmpb    %dl, %al
        jl      .L7
        testb   %dl, %dl
        jne     .L58
.L7:
        movslq  32(%rsp), %r12
        movabsq $-2305966154516004864, %rax
        movl    $5, 116(%rsp)
        leaq    (%rbx,%r12,4), %rdi
        movq    %rdi, %rdx
        shrq    $3, %rdx
        movzbl  (%rdx,%rax), %edx
        movq    %rdi, %rax
        andl    $7, %eax
        addl    $3, %eax
        cmpb    %dl, %al
        jl      .L8
        testb   %dl, %dl
        jne     .L59
.L8:
        pxor    %xmm0, %xmm0
        movabsq $-2305966154516004864, %rdx
        movl    96(%rsp,%r12,4), %eax
        movl    $0, 16(%rdx,%rbp)
        movups  %xmm0, 0(%rbp,%rdx)
        addq    $160, %rsp
        popq    %rbx
        popq    %rbp
        popq    %r12
        ret
.L59:
        call    __asan_report_load4_noabort
        jmp     .L8
.L58:
        call    __asan_report_store4_noabort
        jmp     .L7
.L57:
        call    __asan_report_store4_noabort
        jmp     .L6
.L56:
        call    __asan_report_store4_noabort
        jmp     .L5
.L55:
        call    __asan_report_store4_noabort
        jmp     .L4
.L54:
        call    __asan_report_store4_noabort
        jmp     .L3
.L53:
        movq    %rbx, %rdi
        call    __asan_report_store4_noabort
        jmp     .L2