[PATCH] D43071: [ELF] - Support DSECT, COPY, INFO, OVERLAY output sections attributes.

[Rafael Avila de Espindola via llvm-commits]

I would probably just start with INFO since that is the one you found in
use.

Cheers,
Rafael

George Rimar via Phabricator <reviews at reviews.llvm.org> writes:

> grimar created this revision.
> grimar added reviewers: ruiu, espindola.
> Herald added a subscriber: emaste.
>
> This is PR36298.
>
> (SECT), (COPY), (INFO), (OVERLAY) all have the same effect:
>  section should be marked as non-allocatable.
>
> (https://www.eecs.umich.edu/courses/eecs373/readings/Linker.pdf,
> 3.6.8.1 Output Section Type)
>
>
> https://reviews.llvm.org/D43071
>
> Files:
>   ELF/LinkerScript.cpp
>   ELF/OutputSections.h
>   ELF/ScriptParser.cpp
>   test/ELF/linkerscript/info-section-type.s
>
> Index: test/ELF/linkerscript/info-section-type.s
> ===================================================================
> --- test/ELF/linkerscript/info-section-type.s
> +++ test/ELF/linkerscript/info-section-type.s
> @@ -0,0 +1,38 @@
> +# REQUIRES: x86
> +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
> +
> +## In this test we check that output section types such as
> +## DSECT, COPY, INFO and OVERLAY marks output section as
> +## non-allocatable.
> +
> +# RUN: echo "SECTIONS { .bar : { *(.foo) } };" > %t.script
> +# RUN: ld.lld -o %t --script %t.script %t.o
> +# RUN: llvm-readobj -sections %t | FileCheck %s --check-prefix=DEFAULT
> +# DEFAULT:      Name: .bar
> +# DEFAULT:      Type: SHT_PROGBITS
> +# DEFAULT-NEXT: Flags [
> +# DEFAULT-NEXT:   SHF_ALLOC
> +# DEFAULT-NEXT: ]
> +
> +# RUN: echo "SECTIONS { .bar (DSECT) : { *(.foo) } };" > %t.script
> +# RUN: ld.lld -o %t --script %t.script %t.o
> +# RUN: llvm-readobj -sections %t | FileCheck %s --check-prefix=NONALLOC
> +# NONALLOC:      Name: .bar
> +# NONALLOC:      Type: SHT_PROGBITS
> +# NONALLOC-NEXT: Flags [
> +# NONALLOC-NEXT: ]
> +
> +# RUN: echo "SECTIONS { .bar (COPY) : { *(.foo) } };" > %t.script
> +# RUN: ld.lld -o %t --script %t.script %t.o
> +# RUN: llvm-readobj -sections %t | FileCheck %s --check-prefix=NONALLOC
> +
> +# RUN: echo "SECTIONS { .bar (INFO) : { *(.foo) } };" > %t.script
> +# RUN: ld.lld -o %t --script %t.script %t.o
> +# RUN: llvm-readobj -sections %t | FileCheck %s --check-prefix=NONALLOC
> +
> +# RUN: echo "SECTIONS { .bar (OVERLAY) : { *(.foo) } };" > %t.script
> +# RUN: ld.lld -o %t --script %t.script %t.o
> +# RUN: llvm-readobj -sections %t | FileCheck %s --check-prefix=NONALLOC
> +
> +.section .foo,"a", at progbits
> +.zero 1
> Index: ELF/ScriptParser.cpp
> ===================================================================
> --- ELF/ScriptParser.cpp
> +++ ELF/ScriptParser.cpp
> @@ -617,12 +617,14 @@
>    return V;
>  }
>  
> -// Reads an expression and/or the special directive "(NOLOAD)" for an
> -// output section definition.
> +// Reads an expression and/or the special directive for an output section
> +// definition. Directive can be one of following: "(NOLOAD)", "(DSECT)",
> +// "(COPY)", "(INFO)", "(OVERLAY)".
>  //
>  // An output section name can be followed by an address expression
> -// and/or by "(NOLOAD)". This grammar is not LL(1) because "(" can be
> -// interpreted as either the beginning of some expression or "(NOLOAD)".
> +// and/or directive. This grammar is not LL(1) because "(" can be
> +// interpreted as either the beginning of some expression or begining
> +// of directive.
>  //
>  // https://sourceware.org/binutils/docs/ld/Output-Section-Address.html
>  // https://sourceware.org/binutils/docs/ld/Output-Section-Type.html
> @@ -633,6 +635,12 @@
>        Cmd->Noload = true;
>        return;
>      }
> +    if (consume("DSECT") || consume("COPY") || consume("INFO") ||
> +        consume("OVERLAY")) {
> +      expect(")");
> +      Cmd->Dsect = true;
> +      return;
> +    }
>      Cmd->AddrExpr = readExpr();
>      expect(")");
>    } else {
> Index: ELF/OutputSections.h
> ===================================================================
> --- ELF/OutputSections.h
> +++ ELF/OutputSections.h
> @@ -100,6 +100,7 @@
>    std::string Location;
>    std::string MemoryRegionName;
>    std::string LMARegionName;
> +  bool Dsect = false;
>    bool Noload = false;
>  
>    template <class ELFT> void finalize();
> Index: ELF/LinkerScript.cpp
> ===================================================================
> --- ELF/LinkerScript.cpp
> +++ ELF/LinkerScript.cpp
> @@ -436,6 +436,8 @@
>        Sec->SectionIndex = I++;
>        if (Sec->Noload)
>          Sec->Type = SHT_NOBITS;
> +      if (Sec->Dsect)
> +        Sec->Flags &= ~(uint64_t)SHF_ALLOC;
>      }
>    }
>    Ctx = nullptr;