[lld] r369828 - [ELF] Align the first section of a PT_LOAD even if its type is SHT_NOBITS
Hans Wennborg via llvm-commits
llvm-commits at lists.llvm.org
Fri Sep 6 04:17:12 PDT 2019
Merged to release_90 in r371196.
On Sat, Aug 24, 2019 at 2:39 AM Fangrui Song via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
>
> Author: maskray
> Date: Fri Aug 23 17:41:15 2019
> New Revision: 369828
>
> URL: http://llvm.org/viewvc/llvm-project?rev=369828&view=rev
> Log:
> [ELF] Align the first section of a PT_LOAD even if its type is SHT_NOBITS
>
> Reported at https://reviews.llvm.org/D64930#1642223
>
> If the only section of a PT_LOAD is a SHT_NOBITS section (e.g. .bss), we
> may not align its sh_offset. p_offset of the PT_LOAD will be set to
> sh_offset, and we will get p_offset!=p_vaddr (mod p_align). If such
> executable is mapped by the Linux kernel, it will segfault.
>
> After D64906, this may happen the non-linker script case.
>
> The linker script case has had this issue for a long time.
> This was fixed by rL321657 (but the test linkerscript/nobits-offset.s
> failed to test a SHT_NOBITS section), but broken by rL345154.
>
> Reviewed By: peter.smith
>
> Differential Revision: https://reviews.llvm.org/D66658
>
> Added:
> lld/trunk/test/ELF/nobits-offset.s
> Modified:
> lld/trunk/ELF/Writer.cpp
> lld/trunk/test/ELF/linkerscript/nobits-offset.s
> lld/trunk/test/ELF/relocatable.s
> lld/trunk/test/ELF/relocation-copy-align-common.s
>
> Modified: lld/trunk/ELF/Writer.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=369828&r1=369827&r2=369828&view=diff
> ==============================================================================
> --- lld/trunk/ELF/Writer.cpp (original)
> +++ lld/trunk/ELF/Writer.cpp Fri Aug 23 17:41:15 2019
> @@ -2269,25 +2269,26 @@ template <class ELFT> void Writer<ELFT>:
> // same with its virtual address modulo the page size, so that the loader can
> // load executables without any address adjustment.
> static uint64_t computeFileOffset(OutputSection *os, uint64_t off) {
> - // File offsets are not significant for .bss sections. By convention, we keep
> - // section offsets monotonically increasing rather than setting to zero.
> - if (os->type == SHT_NOBITS)
> - return off;
> -
> - // If the section is not in a PT_LOAD, we just have to align it.
> - if (!os->ptLoad)
> - return alignTo(off, os->alignment);
> -
> // The first section in a PT_LOAD has to have congruent offset and address
> // module the page size.
> - OutputSection *first = os->ptLoad->firstSec;
> - if (os == first) {
> + if (os->ptLoad && os->ptLoad->firstSec == os) {
> uint64_t alignment = std::max<uint64_t>(os->alignment, config->maxPageSize);
> return alignTo(off, alignment, os->addr);
> }
>
> + // File offsets are not significant for .bss sections other than the first one
> + // in a PT_LOAD. By convention, we keep section offsets monotonically
> + // increasing rather than setting to zero.
> + if (os->type == SHT_NOBITS)
> + return off;
> +
> + // If the section is not in a PT_LOAD, we just have to align it.
> + if (!os->ptLoad)
> + return alignTo(off, os->alignment);
> +
> // If two sections share the same PT_LOAD the file offset is calculated
> // using this formula: Off2 = Off1 + (VA2 - VA1).
> + OutputSection *first = os->ptLoad->firstSec;
> return first->offset + os->addr - first->addr;
> }
>
>
> Modified: lld/trunk/test/ELF/linkerscript/nobits-offset.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/linkerscript/nobits-offset.s?rev=369828&r1=369827&r2=369828&view=diff
> ==============================================================================
> --- lld/trunk/test/ELF/linkerscript/nobits-offset.s (original)
> +++ lld/trunk/test/ELF/linkerscript/nobits-offset.s Fri Aug 23 17:41:15 2019
> @@ -2,17 +2,24 @@
> # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
> # RUN: echo "SECTIONS { \
> # RUN: .sec1 (NOLOAD) : { . += 1; } \
> -# RUN: .text : { *(.text) } \
> +# RUN: .bss : { *(.bss) } \
> # RUN: };" > %t.script
> # RUN: ld.lld %t.o -T %t.script -o %t
> -# RUN: llvm-readelf --sections %t | FileCheck %s
> +# RUN: llvm-readelf -S -l %t | FileCheck %s
>
> -# We used to misalign section offsets if the first section in a
> -# PT_LOAD was SHT_NOBITS.
> +## If a SHT_NOBITS section is the only section of a PT_LOAD segment,
> +## p_offset will be set to the sh_offset field of the section. Check we align
> +## sh_offset to sh_addr modulo max-page-size, so that p_vaddr=p_offset (mod
> +## p_align).
>
> -# CHECK: [ 2] .text PROGBITS 0000000000000010 001010 000010 00 AX 0 0 16
> +# CHECK: Name Type Address Off Size ES Flg Lk Inf Al
> +# CHECK: .bss NOBITS 0000000000000400 001400 000001 00 WA 0 0 1024
>
> -.global _start
> -_start:
> - nop
> -.p2align 4
> +# CHECK: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
> +# CHECK: LOAD 0x001400 0x0000000000000400 0x0000000000000400 0x000000 0x000001 RW 0x1000
> +
> +# CHECK: 00 .bss
> +
> +.bss
> +.p2align 10
> +.byte 0
>
> Added: lld/trunk/test/ELF/nobits-offset.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/nobits-offset.s?rev=369828&view=auto
> ==============================================================================
> --- lld/trunk/test/ELF/nobits-offset.s (added)
> +++ lld/trunk/test/ELF/nobits-offset.s Fri Aug 23 17:41:15 2019
> @@ -0,0 +1,21 @@
> +# REQUIRES: aarch64
> +# RUN: llvm-mc -filetype=obj -triple=aarch64 %s -o %t.o
> +# RUN: ld.lld %t.o -o %t
> +# RUN: llvm-readelf -S -l %t | FileCheck %s
> +
> +## If a SHT_NOBITS section is the only section of a PT_LOAD segment,
> +## p_offset will be set to the sh_offset field of the section. Check we align
> +## sh_offset to sh_addr modulo max-page-size, so that p_vaddr=p_offset (mod
> +## p_align).
> +
> +# CHECK: Name Type Address Off Size ES Flg Lk Inf Al
> +# CHECK: .bss NOBITS 0000000000221000 001000 000001 00 WA 0 0 4096
> +
> +# CHECK: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
> +# CHECK: LOAD 0x001000 0x0000000000221000 0x0000000000221000 0x000000 0x000001 RW 0x10000
> +
> +# CHECK: 02 .bss
> +
> +.bss
> +.p2align 12
> +.byte 0
>
> Modified: lld/trunk/test/ELF/relocatable.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/relocatable.s?rev=369828&r1=369827&r2=369828&view=diff
> ==============================================================================
> --- lld/trunk/test/ELF/relocatable.s (original)
> +++ lld/trunk/test/ELF/relocatable.s Fri Aug 23 17:41:15 2019
> @@ -94,7 +94,7 @@
> # CHECKEXE-NEXT: Version: 1
> # CHECKEXE-NEXT: Entry: 0x201000
> # CHECKEXE-NEXT: ProgramHeaderOffset: 0x40
> -# CHECKEXE-NEXT: SectionHeaderOffset: 0x11F8
> +# CHECKEXE-NEXT: SectionHeaderOffset: 0x21A0
> # CHECKEXE-NEXT: Flags [
> # CHECKEXE-NEXT: ]
> # CHECKEXE-NEXT: HeaderSize: 64
>
> Modified: lld/trunk/test/ELF/relocation-copy-align-common.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/relocation-copy-align-common.s?rev=369828&r1=369827&r2=369828&view=diff
> ==============================================================================
> --- lld/trunk/test/ELF/relocation-copy-align-common.s (original)
> +++ lld/trunk/test/ELF/relocation-copy-align-common.s Fri Aug 23 17:41:15 2019
> @@ -15,7 +15,7 @@
> # CHECK-NEXT: SHF_WRITE
> # CHECK-NEXT: ]
> # CHECK-NEXT: Address: 0x203000
> -# CHECK-NEXT: Offset: 0x20B0
> +# CHECK-NEXT: Offset: 0x3000
> # CHECK-NEXT: Size: 16
> # CHECK-NEXT: Link: 0
> # CHECK-NEXT: Info: 0
>
>
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