[lld] r250100 - [ELF2] Sort PPC64 special sections
Hal Finkel via llvm-commits
llvm-commits at lists.llvm.org
Mon Oct 12 14:16:27 PDT 2015
----- Original Message -----
> From: "Rui Ueyama" <ruiu at google.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: "llvm-commits" <llvm-commits at lists.llvm.org>
> Sent: Monday, October 12, 2015 3:59:17 PM
> Subject: Re: [lld] r250100 - [ELF2] Sort PPC64 special sections
>
> On Mon, Oct 12, 2015 at 1:51 PM, Hal Finkel via llvm-commits <
> llvm-commits at lists.llvm.org > wrote:
>
>
> Author: hfinkel
> Date: Mon Oct 12 15:51:48 2015
> New Revision: 250100
>
> URL: http://llvm.org/viewvc/llvm-project?rev=250100&view=rev
> Log:
> [ELF2] Sort PPC64 special sections
>
> PPC64 has several special sections that are intended to be accessed
> from the
> TOC base pointer. When a .got is present, the TOC base pointer is
> .got + 0x8000
> (as specified by the ABI). Furthermore, the glibc startup code
> contains an
> assumption that a 16-bit relocation can hold the offset from the TOC
> base value
> to the beginning of the .toc section. Thus, we need to make sure that
> .toc
> appears after .got. This much, at least, is required in practice. The
> other
> PPC64 special sections (.toc, .toc1, .opd, etc.) should also be close
> by to
> optimize access by smaller TOC-base-pointer offsets.
>
> Modified:
> lld/trunk/ELF/Writer.cpp
> lld/trunk/test/elf2/basic64be.s
>
> Modified: lld/trunk/ELF/Writer.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=250100&r1=250099&r2=250100&view=diff
> ==============================================================================
> --- lld/trunk/ELF/Writer.cpp (original)
> +++ lld/trunk/ELF/Writer.cpp Mon Oct 12 15:51:48 2015
> @@ -14,6 +14,7 @@
> #include "Target.h"
>
> #include "llvm/ADT/SmallPtrSet.h"
> +#include "llvm/ADT/StringSwitch.h"
> #include "llvm/Support/FileOutputBuffer.h"
>
> using namespace llvm;
> @@ -261,6 +262,22 @@ template <class ELFT> void Writer<ELFT>:
> }
> }
>
> +// PPC64 has a number of special SHT_PROGBITS+SHF_ALLOC+SHF_WRITE
> sections that
> +// we would like to make sure appear is a specific order to maximize
> their
> +// coverage by a single signed 16-bit offset from the TOC base
> pointer.
> +// Conversely, the special .tocbss section should be first among all
> SHT_NOBITS
> +// sections. This will put it next to the loaded special PPC64
> sections (and,
> +// thus, within reach of the TOC base pointer).
> +static int getPPC64SectionRank(StringRef SectionName) {
> + return StringSwitch<int>(SectionName)
> + .Case(".tocbss", 0)
> + .Case(".branch_lt", 2)
> + .Case(".toc", 3)
> + .Case(".toc1", 4)
> + .Case(".opd", 5)
> + .Default(1);
> +}
> +
> // Output section ordering is determined by this function.
> template <class ELFT>
> static bool compareOutputSections(OutputSectionBase<ELFT::Is64Bits>
> *A,
> @@ -302,7 +319,10 @@ static bool compareOutputSections(Output
> // them is a p_memsz that is larger than p_filesz. Seeing that it
> // zeros the end of the PT_LOAD, so that has to correspond to the
> // nobits sections.
> - return A->getType() != SHT_NOBITS && B->getType() == SHT_NOBITS;
> + if (A->getType() != SHT_NOBITS && B->getType() == SHT_NOBITS)
> + return true;
>
>
>
> This should be
>
>
> if (A->getType() != B->getType())
> return A->getType() != SHT_NOBITS && B->getType() == SHT_NOBITS;
>
>
> or otherwise this function does not guarantee weak strict ordering.
> Sorry for not noticing earlier.
>
Indeed; good point. r250109.
-Hal
>
> +
> + return getPPC64SectionRank(A->getName()) <
> getPPC64SectionRank(B->getName());
> }
>
> // Until this function is called, common symbols do not belong to any
> section.
>
> Modified: lld/trunk/test/elf2/basic64be.s
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf2/basic64be.s?rev=250100&r1=250099&r2=250100&view=diff
> ==============================================================================
> --- lld/trunk/test/elf2/basic64be.s (original)
> +++ lld/trunk/test/elf2/basic64be.s Mon Oct 12 15:51:48 2015
> @@ -9,6 +9,14 @@
> _start:
> .quad .Lfoo,.TOC. at tocbase,0
>
> +# generate .toc and .toc1 sections to make sure that the ordering is
> as
> +# intended (.toc before .toc1, and both before .opd).
> +.section ".toc1","aw"
> +.quad 22, 37, 89, 47
> +
> +.section ".toc","aw"
> +.quad 45, 86, 72, 24
> +
> .text
> .Lfoo:
> li 0,1
> @@ -28,17 +36,17 @@ _start:
> # CHECK-NEXT: Type: Executable (0x2)
> # CHECK-NEXT: Machine: EM_PPC64 (0x15)
> # CHECK-NEXT: Version: 1
> -# CHECK-NEXT: Entry: 0x10020000
> +# CHECK-NEXT: Entry: 0x10020040
> # CHECK-NEXT: ProgramHeaderOffset: 0x40
> -# CHECK-NEXT: SectionHeaderOffset: 0x20078
> +# CHECK-NEXT: SectionHeaderOffset: 0x200C8
> # CHECK-NEXT: Flags [ (0x0)
> # CHECK-NEXT: ]
> # CHECK-NEXT: HeaderSize: 64
> # CHECK-NEXT: ProgramHeaderEntrySize: 56
> # CHECK-NEXT: ProgramHeaderCount: 4
> # CHECK-NEXT: SectionHeaderEntrySize: 64
> -# CHECK-NEXT: SectionHeaderCount: 7
> -# CHECK-NEXT: StringTableSectionIndex: 6
> +# CHECK-NEXT: SectionHeaderCount: 9
> +# CHECK-NEXT: StringTableSectionIndex: 8
> # CHECK-NEXT: }
> # CHECK-NEXT: Sections [
> # CHECK-NEXT: Section {
> @@ -55,18 +63,18 @@ _start:
> # CHECK-NEXT: AddressAlignment: 0
> # CHECK-NEXT: EntrySize: 0
> # CHECK-NEXT: SectionData (
> -# CHECK: )
> +# CHECK-NEXT: )
> # CHECK-NEXT: }
> # CHECK-NEXT: Section {
> # CHECK-NEXT: Index: 1
> -# CHECK-NEXT: Name: .text
> +# CHECK-NEXT: Name: .text (1)
> # CHECK-NEXT: Type: SHT_PROGBITS (0x1)
> # CHECK-NEXT: Flags [ (0x6)
> # CHECK-NEXT: SHF_ALLOC (0x2)
> # CHECK-NEXT: SHF_EXECINSTR (0x4)
> # CHECK-NEXT: ]
> # CHECK-NEXT: Address: 0x10010000
> -# CHECK-NEXT: Offset: 0x1000
> +# CHECK-NEXT: Offset: 0x10000
> # CHECK-NEXT: Size: 12
> # CHECK-NEXT: Link: 0
> # CHECK-NEXT: Info: 0
> @@ -77,7 +85,7 @@ _start:
> # CHECK-NEXT: }
> # CHECK-NEXT: Section {
> # CHECK-NEXT: Index: 2
> -# CHECK-NEXT: Name: .data
> +# CHECK-NEXT: Name: .data (45)
> # CHECK-NEXT: Type: SHT_PROGBITS (0x1)
> # CHECK-NEXT: Flags [ (0x3)
> # CHECK-NEXT: SHF_ALLOC (0x2)
> @@ -95,34 +103,74 @@ _start:
> # CHECK-NEXT: }
> # CHECK-NEXT: Section {
> # CHECK-NEXT: Index: 3
> -# CHECK-NEXT: Name: .opd
> +# CHECK-NEXT: Name: .toc (24)
> # CHECK-NEXT: Type: SHT_PROGBITS (0x1)
> # CHECK-NEXT: Flags [ (0x3)
> # CHECK-NEXT: SHF_ALLOC (0x2)
> # CHECK-NEXT: SHF_WRITE (0x1)
> # CHECK-NEXT: ]
> # CHECK-NEXT: Address: 0x10020000
> -# CHECK-NEXT: Offset: 0x2000
> -# CHECK-NEXT: Size: 24
> +# CHECK-NEXT: Offset: 0x20000
> +# CHECK-NEXT: Size: 32
> # CHECK-NEXT: Link: 0
> # CHECK-NEXT: Info: 0
> # CHECK-NEXT: AddressAlignment: 1
> # CHECK-NEXT: EntrySize: 0
> # CHECK-NEXT: SectionData (
> -# CHECK-NEXT: 0000: 00000000 10010000 00000000 00000000
> |................|
> -# CHECK-NEXT: 0010: 00000000 00000000 |........|
> +# CHECK-NEXT: 0000: 00000000 0000002D 00000000 00000056
> |.......-.......V|
> +# CHECK-NEXT: 0010: 00000000 00000048 00000000 00000018
> |.......H........|
> # CHECK-NEXT: )
> # CHECK-NEXT: }
> # CHECK-NEXT: Section {
> # CHECK-NEXT: Index: 4
> -# CHECK-NEXT: Name: .bss
> +# CHECK-NEXT: Name: .toc1 (51)
> +# CHECK-NEXT: Type: SHT_PROGBITS (0x1)
> +# CHECK-NEXT: Flags [ (0x3)
> +# CHECK-NEXT: SHF_ALLOC (0x2)
> +# CHECK-NEXT: SHF_WRITE (0x1)
> +# CHECK-NEXT: ]
> +# CHECK-NEXT: Address: 0x10020020
> +# CHECK-NEXT: Offset: 0x20020
> +# CHECK-NEXT: Size: 32
> +# CHECK-NEXT: Link: 0
> +# CHECK-NEXT: Info: 0
> +# CHECK-NEXT: AddressAlignment: 1
> +# CHECK-NEXT: EntrySize: 0
> +# CHECK-NEXT: SectionData (
> +# CHECK-NEXT: 0000: 00000000 00000016 00000000 00000025
> |...............%|
> +# CHECK-NEXT: 0010: 00000000 00000059 00000000 0000002F
> |.......Y......./|
> +# CHECK-NEXT: )
> +# CHECK-NEXT: }
> +# CHECK-NEXT: Section {
> +# CHECK-NEXT: Index: 5
> +# CHECK-NEXT: Name: .opd (19)
> +# CHECK-NEXT: Type: SHT_PROGBITS (0x1)
> +# CHECK-NEXT: Flags [ (0x3)
> +# CHECK-NEXT: SHF_ALLOC (0x2)
> +# CHECK-NEXT: SHF_WRITE (0x1)
> +# CHECK-NEXT: ]
> +# CHECK-NEXT: Address: 0x10020040
> +# CHECK-NEXT: Offset: 0x20040
> +# CHECK-NEXT: Size: 24
> +# CHECK-NEXT: Link: 0
> +# CHECK-NEXT: Info: 0
> +# CHECK-NEXT: AddressAlignment: 1
> +# CHECK-NEXT: EntrySize: 0
> +# CHECK-NEXT: SectionData (
> +# CHECK-NEXT: 0000: 00000000 10010000 00000000 00000000
> |................|
> +# CHECK-NEXT: 0010: 00000000 00000000 |........|
> +# CHECK-NEXT: )
> +# CHECK-NEXT: }
> +# CHECK-NEXT: Section {
> +# CHECK-NEXT: Index: 6
> +# CHECK-NEXT: Name: .bss (14)
> # CHECK-NEXT: Type: SHT_NOBITS (0x8)
> # CHECK-NEXT: Flags [ (0x3)
> # CHECK-NEXT: SHF_ALLOC (0x2)
> # CHECK-NEXT: SHF_WRITE (0x1)
> # CHECK-NEXT: ]
> -# CHECK-NEXT: Address: 0x10020018
> -# CHECK-NEXT: Offset: 0x20018
> +# CHECK-NEXT: Address: 0x10020058
> +# CHECK-NEXT: Offset: 0x20058
> # CHECK-NEXT: Size: 0
> # CHECK-NEXT: Link: 0
> # CHECK-NEXT: Info: 0
> @@ -130,15 +178,15 @@ _start:
> # CHECK-NEXT: EntrySize: 0
> # CHECK-NEXT: }
> # CHECK-NEXT: Section {
> -# CHECK-NEXT: Index: 5
> -# CHECK-NEXT: Name: .symtab
> -# CHECK-NEXT: Type: SHT_SYMTAB
> -# CHECK-NEXT: Flags [
> +# CHECK-NEXT: Index: 7
> +# CHECK-NEXT: Name: .symtab (37)
> +# CHECK-NEXT: Type: SHT_SYMTAB (0x2)
> +# CHECK-NEXT: Flags [ (0x0)
> # CHECK-NEXT: ]
> # CHECK-NEXT: Address: 0x0
> -# CHECK-NEXT: Offset: 0x20018
> +# CHECK-NEXT: Offset: 0x20058
> # CHECK-NEXT: Size: 48
> -# CHECK-NEXT: Link: 6
> +# CHECK-NEXT: Link: 8
> # CHECK-NEXT: Info: 1
> # CHECK-NEXT: AddressAlignment: 8
> # CHECK-NEXT: EntrySize: 24
> @@ -146,14 +194,14 @@ _start:
> # CHECK: )
> # CHECK-NEXT: }
> # CHECK-NEXT: Section {
> -# CHECK-NEXT: Index: 6
> -# CHECK-NEXT: Name: .strtab
> +# CHECK-NEXT: Index: 8
> +# CHECK-NEXT: Name: .strtab (29)
> # CHECK-NEXT: Type: SHT_STRTAB (0x3)
> # CHECK-NEXT: Flags [ (0x0)
> # CHECK-NEXT: ]
> # CHECK-NEXT: Address: 0x0
> -# CHECK-NEXT: Offset: 0x20048
> -# CHECK-NEXT: Size: 46
> +# CHECK-NEXT: Offset: 0x20088
> +# CHECK-NEXT: Size: 57
> # CHECK-NEXT: Link: 0
> # CHECK-NEXT: Info: 0
> # CHECK-NEXT: AddressAlignment: 1
> @@ -205,8 +253,8 @@ _start:
> # CHECK-NEXT: Offset: 0x2000
> # CHECK-NEXT: VirtualAddress: 0x10020000
> # CHECK-NEXT: PhysicalAddress: 0x10020000
> -# CHECK-NEXT: FileSize: 24
> -# CHECK-NEXT: MemSize: 24
> +# CHECK-NEXT: FileSize: 88
> +# CHECK-NEXT: MemSize: 88
> # CHECK-NEXT: Flags [ (0x6)
> # CHECK-NEXT: PF_R (0x4)
> # CHECK-NEXT: PF_W (0x2)
>
>
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>
--
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory
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