[PATCH] Eliminate the .eh_frame sections from the aarch64 vmlinux and kernel modules
William Cohen
wcohen at redhat.com
Fri Jan 22 07:36:12 PST 2016
On 01/22/2016 10:02 AM, Mark Rutland wrote:
> On Fri, Jan 22, 2016 at 09:43:25AM -0500, William Cohen wrote:
>> On 01/22/2016 02:41 AM, Ard Biesheuvel wrote:
>>> On 22 January 2016 at 04:56, William Cohen <wcohen at redhat.com> wrote:
>>>> By default the aarch64 gcc generates .eh_frame sections. Unlike
>>>> .debug_frame sections, the .eh_frame sections are loaded into memory
>>>> when the associated code is loaded. On an example kernel being built
>>>> with this default the .eh_frame section in vmlinux used an extra 1.7MB
>>>> of memory. The x86 disables the creation of the .eh_frame section.
>>>> The aarch64 should probably do the same to save some memory.
>>>>
>>>
>>> With my GCC-4.9.3 Linaro toolchain, I am not getting .eh_frame
>>> sections only .debug_frame sections. The patch still makes sense imo,
>>> but it appears to be redundant in some cases, and it would be useful
>>> to figure out why. Which toolchain have you tested this with?
>>
>> Hi,
>>
>> I have observed the .eh_frame being generated with gcc-5.3.1 that is in Fedora 23.
>
> FWIW, I do not see this with the Linaro 15.08 GCC 5.1.1.
>
> It would be interesting to know if that's something that changed
> upstream between 5.1.x and 5.3.x or if that's a Fedora-specific
> configuration option, but either way the patch seems reasonable.
>
> Thanks,
> Mark.
>
Hi Mark,
The sizes of the resulting vmlinux files are pretty similar. However, I could see the change in available memory when I booted the kernels. To see the change without booting you need to use eu-readelf. The vmlinux.eh_frame is the original build and the vmlinux.no_eh_frame is the build with the -fno-asynchronous-unwind-tables. The "LOAD" line of "eu-readelf -l" show MemSiz drop. The "ue-readelf -S" output shows movement of the data moved from the .eh_frame to the .debug_frame section. Below is the various eu-readelf output.
-Will
[linaro at localhost kernel]$ eu-readelf -l vmlinux.eh_frame
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
LOAD 0x010000 0xffffffc000080000 0xffffffc000080000 0xe33800 0x1b2a648 RWE 0x10000
NOTE 0xd04a00 0xffffffc000d74a00 0xffffffc000d74a00 0x000024 0x000024 R 0x4
GNU_STACK 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW 0x10
Section to Segment mapping:
Segment Sections...
00 .head.text .text .text.init .rodata .eh_frame .init.rodata.str1.8 .init.eh_frame __bug_table .pci_fixup __ksymtab __ksymtab_gpl __ksymtab_strings __param __modver __ex_table .notes .init.text .exit.text .init.data .data..percpu .altinstructions .altinstr_replacement .data .pecoff_edata_padding .bss
01 .notes
02
[linaro at localhost kernel]$ eu-readelf -l vmlinux.no_eh_frame
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
LOAD 0x010000 0xffffffc000080000 0xffffffc000080000 0xc83800 0x197a648 RWE 0x10000
NOTE 0xb53a00 0xffffffc000bc3a00 0xffffffc000bc3a00 0x000024 0x000024 R 0x4
GNU_STACK 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW 0x10
Section to Segment mapping:
Segment Sections...
00 .head.text .text .text.init .rodata .init.rodata.str1.8 __bug_table .pci_fixup __ksymtab __ksymtab_gpl __ksymtab_strings __param __modver __ex_table .notes .init.text .exit.text .init.data .data..percpu .altinstructions .altinstr_replacement .data .pecoff_edata_padding .bss
01 .notes
02
[linaro at localhost kernel]$ eu-readelf -S vmlinux.eh_frame
There are 37 section headers, starting at offset 0x8b07650:
Section Headers:
[Nr] Name Type Addr Off Size ES Flags Lk Inf Al
[ 0] NULL 0000000000000000 00000000 00000000 0 0 0 0
[ 1] .head.text PROGBITS ffffffc000080000 00010000 00002000 0 AX 0 0 4096
[ 2] .text PROGBITS ffffffc000082000 00012000 00807890 0 AX 0 0 4096
[ 3] .text.init PROGBITS ffffffc000889890 00819890 00000090 0 AX 0 0 16
[ 4] .rodata PROGBITS ffffffc00088a000 0081a000 002d22a0 0 A 0 0 4096
[ 5] .eh_frame PROGBITS ffffffc000b5c2a0 00aec2a0 001b0960 0 A 0 0 8
[ 6] .init.rodata.str1.8 PROGBITS ffffffc000d0cc00 00c9cc00 00000768 1 AMS 0 0 8
[ 7] .init.eh_frame PROGBITS ffffffc000d0d368 00c9d368 00000530 0 A 0 0 8
[ 8] __bug_table PROGBITS ffffffc000d0d898 00c9d898 000147b4 0 A 0 0 4
[ 9] .pci_fixup PROGBITS ffffffc000d22050 00cb2050 00002358 0 A 0 0 8
[10] __ksymtab PROGBITS ffffffc000d243a8 00cb43a8 00012360 0 A 0 0 8
[11] __ksymtab_gpl PROGBITS ffffffc000d36708 00cc6708 0000f610 0 A 0 0 8
[12] __ksymtab_strings PROGBITS ffffffc000d45d18 00cd5d18 00028fa4 0 A 0 0 1
[13] __param PROGBITS ffffffc000d6ecc0 00cfecc0 00002580 0 A 0 0 8
[14] __modver PROGBITS ffffffc000d71240 00d01240 00000dc0 0 A 0 0 8
[15] __ex_table PROGBITS ffffffc000d72000 00d02000 00002a00 0 A 0 0 8
[16] .notes NOTE ffffffc000d74a00 00d04a00 00000024 0 A 0 0 4
[17] .init.text PROGBITS ffffffc000d75000 00d05000 000394b8 0 AX 0 0 16
[18] .exit.text PROGBITS ffffffc000dae4b8 00d3e4b8 00002f20 0 AX 0 0 4
[19] .init.data PROGBITS ffffffc000db13e0 00d413e0 00045bd8 0 WA 0 0 32
[20] .data..percpu PROGBITS ffffffc000df7000 00d87000 00006cc0 0 WA 0 0 64
[21] .altinstructions PROGBITS ffffffc000dfe000 00d8e000 000091c8 0 A 0 0 1
[22] .altinstr_replacement PROGBITS ffffffc000e071c8 00d971c8 00003098 0 AX 0 0 1
[23] .data PROGBITS ffffffc000e0b000 00d9b000 000a8668 0 WA 0 0 4096
[24] .pecoff_edata_padding PROGBITS ffffffc000eb3668 00e43668 00000198 0 WA 0 0 1
[25] .bss NOBITS ffffffc000eb4000 00e43800 00cf6648 0 WA 0 0 4096
[26] .comment PROGBITS 0000000000000000 00e43800 0000002c 1 MS 0 0 1
[27] .debug_line PROGBITS 0000000000000000 00e4382c 00645ee5 0 0 0 1
[28] .debug_info PROGBITS 0000000000000000 01489711 05f6205d 0 0 0 1
[29] .debug_abbrev PROGBITS 0000000000000000 073eb76e 00294bdc 0 0 0 1
[30] .debug_aranges PROGBITS 0000000000000000 07680350 0001dfd0 0 0 0 16
[31] .debug_ranges PROGBITS 0000000000000000 0769e320 0046a880 0 0 0 16
[32] .debug_str PROGBITS 0000000000000000 07b08ba0 00223043 1 MS 0 0 1
[33] .debug_loc PROGBITS 0000000000000000 07d2bbe3 00976164 0 0 0 1
[34] .shstrtab STRTAB 0000000000000000 086a1d47 00000193 0 0 0 1
[35] .symtab SYMTAB 0000000000000000 086a1ee0 002f4ba0 24 36 102756 8
[36] .strtab STRTAB 0000000000000000 08996a80 00170bcc 0 0 0 1
[linaro at localhost kernel]$ eu-readelf -S vmlinux.no_eh_frame
There are 36 section headers, starting at offset 0x8b3b950:
Section Headers:
[Nr] Name Type Addr Off Size ES Flags Lk Inf Al
[ 0] NULL 0000000000000000 00000000 00000000 0 0 0 0
[ 1] .head.text PROGBITS ffffffc000080000 00010000 00002000 0 AX 0 0 4096
[ 2] .text PROGBITS ffffffc000082000 00012000 00807890 0 AX 0 0 4096
[ 3] .text.init PROGBITS ffffffc000889890 00819890 00000090 0 AX 0 0 16
[ 4] .rodata PROGBITS ffffffc00088a000 0081a000 002d22a0 0 A 0 0 4096
[ 5] .init.rodata.str1.8 PROGBITS ffffffc000b5c2a0 00aec2a0 00000768 1 AMS 0 0 8
[ 6] __bug_table PROGBITS ffffffc000b5ca08 00aeca08 000147b4 0 A 0 0 4
[ 7] .pci_fixup PROGBITS ffffffc000b711c0 00b011c0 00002358 0 A 0 0 8
[ 8] __ksymtab PROGBITS ffffffc000b73518 00b03518 00012360 0 A 0 0 8
[ 9] __ksymtab_gpl PROGBITS ffffffc000b85878 00b15878 0000f610 0 A 0 0 8
[10] __ksymtab_strings PROGBITS ffffffc000b94e88 00b24e88 00028fa4 0 A 0 0 1
[11] __param PROGBITS ffffffc000bbde30 00b4de30 00002580 0 A 0 0 8
[12] __modver PROGBITS ffffffc000bc03b0 00b503b0 00000c50 0 A 0 0 8
[13] __ex_table PROGBITS ffffffc000bc1000 00b51000 00002a00 0 A 0 0 8
[14] .notes NOTE ffffffc000bc3a00 00b53a00 00000024 0 A 0 0 4
[15] .init.text PROGBITS ffffffc000bc4000 00b54000 00039498 0 AX 0 0 16
[16] .exit.text PROGBITS ffffffc000bfd498 00b8d498 00002f20 0 AX 0 0 4
[17] .init.data PROGBITS ffffffc000c003c0 00b903c0 00045bd8 0 WA 0 0 32
[18] .data..percpu PROGBITS ffffffc000c46000 00bd6000 00006cc0 0 WA 0 0 64
[19] .altinstructions PROGBITS ffffffc000c4d000 00bdd000 000091c8 0 A 0 0 1
[20] .altinstr_replacement PROGBITS ffffffc000c561c8 00be61c8 00003098 0 AX 0 0 1
[21] .data PROGBITS ffffffc000c5a000 00bea000 000a9668 0 WA 0 0 4096
[22] .pecoff_edata_padding PROGBITS ffffffc000d03668 00c93668 00000198 0 WA 0 0 1
[23] .bss NOBITS ffffffc000d04000 00c93800 00cf6648 0 WA 0 0 4096
[24] .comment PROGBITS 0000000000000000 00c93800 0000002c 1 MS 0 0 1
[25] .debug_line PROGBITS 0000000000000000 00c9382c 00646080 0 0 0 1
[26] .debug_info PROGBITS 0000000000000000 012d98ac 05f61fab 0 0 0 1
[27] .debug_abbrev PROGBITS 0000000000000000 0723b857 00294bd3 0 0 0 1
[28] .debug_aranges PROGBITS 0000000000000000 074d0430 0001dfd0 0 0 0 16
[29] .debug_ranges PROGBITS 0000000000000000 074ee400 0046ad10 0 0 0 16
[30] .debug_frame PROGBITS 0000000000000000 07959110 001e35c8 0 0 0 8
[31] .debug_str PROGBITS 0000000000000000 07b3c6d8 002230a2 1 MS 0 0 1
[32] .debug_loc PROGBITS 0000000000000000 07d5f77a 009768ea 0 0 0 1
[33] .shstrtab STRTAB 0000000000000000 086d6064 00000191 0 0 0 1
[34] .symtab SYMTAB 0000000000000000 086d61f8 002f4b88 24 35 102755 8
[35] .strtab STRTAB 0000000000000000 089cad80 00170bcc 0 0 0 1
More information about the linux-arm-kernel
mailing list