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SubjectRe: [PATCH] m68k: add missing SOFTIRQENTRY_TEXT linker section
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Hi Geert,

On 14/11/17 18:11, Geert Uytterhoeven wrote:
> On Tue, Nov 14, 2017 at 7:04 AM, Greg Ungerer <gerg@linux-m68k.org> wrote:
>> Commit be7635e7287e ("arch, ftrace: for KASAN put hard/soft IRQ entries
>> into separate sections") added a new linker section, SOFTIRQENTRY_TEXT,
>> to the linker scripts for most architectures. It didn't add it to any of
>> the linker scripts for the m68k architecture. This was not really a problem
>> because it is only defined if either of CONFIG_FUNCTION_GRAPH_TRACER or
>> CONFIG_KASAN are enabled - which can never be true for m68k.
>>
>> However commit 229a71860547 ("irq: Make the irqentry text section
>> unconditional") means that SOFTIRQENTRY_TEXT is now always defined. So on
>> m68k we now end up with a separate ELF section for .softirqentry.text
>> instead of it being part of the .text section. On some m68k targets in some
>
> Nice catch!
>
> +10 other architectures also don't have the section.
>
>> configurations this can also cause a fatal link error:
>>
>> LD vmlinux
>> /usr/local/bin/../m68k-uclinux/bin/ld.real: section .softirqentry.text loaded at [0000000010de10c0,0000000010de12dd] overlaps section .rodata loaded at [0000000010de10c0,0000000010e0fd67]
>
> How does it cause the overlap?

The 68VZ328 uCdimm target has an unusual layout and normally it is built
as an "in-rom" image. Using objdump to dump the headers for a 4.13 build
gives this type of layout:

linux/vmlinux: file format elf32-m68k

Sections:
Idx Name Size VMA LMA File off Algn
0 .romvec 00000108 10c10000 10c10000 00222000 2**0
CONTENTS, READONLY
1 .text 001d0ee0 10c10400 10c10400 00000400 2**2
CONTENTS, ALLOC, LOAD, READONLY, CODE
2 .rodata 0002eca8 00020000 10de12e0 001d2000 2**4
CONTENTS, ALLOC, LOAD, DATA
3 __param 00000258 0004eca8 10e0ff88 00200ca8 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 __modver 00000100 0004ef00 10e101e0 00200f00 2**1
CONTENTS, ALLOC, LOAD, READONLY, DATA
5 .data 00012440 0004f000 10e102e0 00201000 2**5
CONTENTS, ALLOC, LOAD, DATA
6 .init.text 0000c39a 00062000 10e232e0 00214000 2**1
CONTENTS, ALLOC, LOAD, READONLY, CODE
7 .init.data 00001c64 0006e39c 10e2f67c 0022039c 2**2
CONTENTS, ALLOC, LOAD, DATA
8 .data..percpu 00000000 00070000 00070000 00222108 2**0
CONTENTS, ALLOC, LOAD, DATA
9 .bss 0001407c 00070000 10e312e0 00222000 2**4
ALLOC
10 .comment 00000011 00000000 00000000 00222108 2**0
CONTENTS, READONLY

The 4.14 link tries to put the .softirqentry.text section strait after
the .text section. But that has already been calculated as the offset
for the .rodata. Notice that the start address (000000010de10c0) is
identical in the error message.


> For me, "readelf -S vmlinux" gives:
>
> There are 21 section headers, starting at offset 0x524850:
>
> Section Headers:
> [Nr] Name Type Addr Off Size ES Flg Lk Inf Al
> [ 0] NULL 00000000 000000 000000 00 0 0 0
> [ 1] .text PROGBITS 00001000 001000 2dacb4 00 AX 0 0 4
> [ 2] .softirqentry.tex PROGBITS 002dbcb4 2dbcb4 0001a0 00 AX 0 0 2
> [ 3] __ex_table PROGBITS 002dbe60 2dbe60 0027f0 00 A 0 0 4
> [ 4] .rodata PROGBITS 002df000 2df000 09ee20 00 WA 0 0 16
> [ 5] __ksymtab PROGBITS 0037de20 37de20 006538 00 A 0 0 2
> [ 6] __ksymtab_gpl PROGBITS 00384358 384358 003f08 00 A 0 0 2
> [ 7] __ksymtab_strings PROGBITS 00388260 388260 01747d 00 A 0 0 1
> [ 8] __param PROGBITS 0039f6e0 39f6e0 000924 00 A 0 0 4
> [ 9] __modver PROGBITS 003a0004 3a0004 000ffc 00 A 0 0 2
> [10] .data PROGBITS 003a1000 3a1000 021c20 00 WA 0 0 32
> [11] .bss NOBITS 003c2c20 3c2c20 02b2fc 00 WA 0 0 16
> [12] .init.text PROGBITS 003ee000 3c4000 01a4b2 00 AX 0 0 4
> [13] .init.data PROGBITS 004084b4 3de4b4 008180 00 WA 0 0 4
> [14] .m68k_fixup PROGBITS 00410634 3e6634 001140 00 WA 0 0 1
> [15] .notes NOTE 00411774 3e7774 000024 00 A 0 0 4
> [16] .init_end NOBITS 00411798 3e7798 000868 00 WA 0 0 1
> [17] .comment PROGBITS 00000000 3e7798 000039 01 MS 0 0 1
> [18] .shstrtab STRTAB 00000000 524791 0000bd 00 0 0 1
> [19] .symtab SYMTAB 00000000 3e77d4 0a66e0 10
> 20 32238 4
> [20] .strtab STRTAB 00000000 48deb4 0968dd 00 0 0 1
> Key to Flags:
> W (write), A (alloc), X (execute), M (merge), S (strings)
> I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
> O (extra OS processing required) o (OS specific), p (processor specific)

For most of our other no-MMU links we end up with something similar and
that works ok for direct loads into RAM.

Regards
Greg



>> To fix add in the missing SOFTIRQENTRY_TEXT section into the m68k linker
>> scripts. I noticed that m68k is also missing the IRQENTRY_TEXT section,
>> so this patch also adds an entry for that too.
>>
>> Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>
>> ---
>> arch/m68k/kernel/vmlinux-nommu.lds | 2 ++
>> arch/m68k/kernel/vmlinux-std.lds | 2 ++
>> arch/m68k/kernel/vmlinux-sun3.lds | 2 ++
>> 3 files changed, 6 insertions(+)
>>
>> diff --git a/arch/m68k/kernel/vmlinux-nommu.lds b/arch/m68k/kernel/vmlinux-nommu.lds
>> index 3aa571a..cf6edda 100644
>> --- a/arch/m68k/kernel/vmlinux-nommu.lds
>> +++ b/arch/m68k/kernel/vmlinux-nommu.lds
>> @@ -45,6 +45,8 @@ SECTIONS {
>> .text : {
>> HEAD_TEXT
>> TEXT_TEXT
>> + IRQENTRY_TEXT
>> + SOFTIRQENTRY_TEXT
>> SCHED_TEXT
>> CPUIDLE_TEXT
>> LOCK_TEXT
>> diff --git a/arch/m68k/kernel/vmlinux-std.lds b/arch/m68k/kernel/vmlinux-std.lds
>> index 89172b8..625a578 100644
>> --- a/arch/m68k/kernel/vmlinux-std.lds
>> +++ b/arch/m68k/kernel/vmlinux-std.lds
>> @@ -16,6 +16,8 @@ SECTIONS
>> .text : {
>> HEAD_TEXT
>> TEXT_TEXT
>> + IRQENTRY_TEXT
>> + SOFTIRQENTRY_TEXT
>> SCHED_TEXT
>> CPUIDLE_TEXT
>> LOCK_TEXT
>> diff --git a/arch/m68k/kernel/vmlinux-sun3.lds b/arch/m68k/kernel/vmlinux-sun3.lds
>> index 293990e..9868270 100644
>> --- a/arch/m68k/kernel/vmlinux-sun3.lds
>> +++ b/arch/m68k/kernel/vmlinux-sun3.lds
>> @@ -16,6 +16,8 @@ SECTIONS
>> .text : {
>> HEAD_TEXT
>> TEXT_TEXT
>> + IRQENTRY_TEXT
>> + SOFTIRQENTRY_TEXT
>> SCHED_TEXT
>> CPUIDLE_TEXT
>> LOCK_TEXT
>
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
> -- Linus Torvalds
>

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