[PATCH] D43632: [ELF] - Add testcase documenting flags assigned when empty synthetic section is removed.

[Rafael Avila de Espindola via llvm-commits]

LGTM

It is not immediately clear what is the best behavior, but having a test
for it is a good thing.

BTW, what does ld.bfd outputs?

Cheers,
Rafael


George Rimar via Phabricator via llvm-commits
<llvm-commits at lists.llvm.org> writes:

> grimar created this revision.
> grimar added reviewers: ruiu, espindola, jhenderson.
> Herald added subscribers: arichardson, emaste.
>
> This responds to PR36475,
>
> r325763 led to unexprected layout change, though
> new behavior seems to be more correct.
>
> Previously we could have following script:
>
>   .foo : { *(.foo) } 
>   .bar : { *(.synthetic_empty) BYTE(0x11) }}
>
> where `synthetic_empty` is a synthetic section which is empty and
> hence removed by linker.
> Before r325763 `.bar` would receive section flags from .synthetic_empty,
> but after this revision it receives flags the same as `.foo` section has.
>
> It is the same as if there would not be any `synthetic_empty` section in a script,
> so looks reasonable and consistent behavior:
>
>   .foo : { *(.foo) } 
>   .bar : { BYTE(0x11) }}
>
> Patch adds testcase to document it.
>
>
> https://reviews.llvm.org/D43632
>
> Files:
>   test/ELF/linkerscript/empty-synthetic-removed-flags.s
>
>
> Index: test/ELF/linkerscript/empty-synthetic-removed-flags.s
> ===================================================================
> --- test/ELF/linkerscript/empty-synthetic-removed-flags.s
> +++ test/ELF/linkerscript/empty-synthetic-removed-flags.s
> @@ -0,0 +1,32 @@
> +# REQUIRES: x86
> +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
> +# RUN: echo "SECTIONS {                          \
> +# RUN:         .foo : { *(.foo) }                \
> +# RUN:         .bar : { *(.got.plt) BYTE(0x11) }}" > %t.script
> +# RUN: ld.lld -o %t --script %t.script %t.o
> +# RUN: llvm-readobj -s %t | FileCheck %s
> +
> +## We have ".got.plt" synthetic section with SHF_ALLOC|SHF_WRITE flags.
> +## It is empty, so linker removes it, but it have to keep ".got.plt" output
> +## section because of BYTE command. Here we check that result output section
> +## gets the same flags as previous allocatable section and does not get
> +## SHF_WRITE flag from removed syntethic input section.
> +
> +# CHECK:     Section {
> +# CHECK:       Index: 2
> +# CHECK:       Name: .bar
> +# CHECK-NEXT:  Type: SHT_PROGBITS
> +# CHECK-NEXT:  Flags [
> +# CHECK-NEXT:    SHF_ALLOC
> +# CHECK-NEXT:    SHF_EXECINSTR
> +# CHECK-NEXT:  ]
> +
> +## Check flags are the same if we omit empty synthetic section in script.
> +# RUN: echo "SECTIONS {              \
> +# RUN:         .foo : { *(.foo) }    \
> +# RUN:         .bar : { BYTE(0x11) }}" > %t.script
> +# RUN: ld.lld -o %t --script %t.script %t.o
> +# RUN: llvm-readobj -s %t | FileCheck %s
> +
> +.section .foo,"ax"
> +.quad 0
>
>
> Index: test/ELF/linkerscript/empty-synthetic-removed-flags.s
> ===================================================================
> --- test/ELF/linkerscript/empty-synthetic-removed-flags.s
> +++ test/ELF/linkerscript/empty-synthetic-removed-flags.s
> @@ -0,0 +1,32 @@
> +# REQUIRES: x86
> +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
> +# RUN: echo "SECTIONS {                          \
> +# RUN:         .foo : { *(.foo) }                \
> +# RUN:         .bar : { *(.got.plt) BYTE(0x11) }}" > %t.script
> +# RUN: ld.lld -o %t --script %t.script %t.o
> +# RUN: llvm-readobj -s %t | FileCheck %s
> +
> +## We have ".got.plt" synthetic section with SHF_ALLOC|SHF_WRITE flags.
> +## It is empty, so linker removes it, but it have to keep ".got.plt" output
> +## section because of BYTE command. Here we check that result output section
> +## gets the same flags as previous allocatable section and does not get
> +## SHF_WRITE flag from removed syntethic input section.
> +
> +# CHECK:     Section {
> +# CHECK:       Index: 2
> +# CHECK:       Name: .bar
> +# CHECK-NEXT:  Type: SHT_PROGBITS
> +# CHECK-NEXT:  Flags [
> +# CHECK-NEXT:    SHF_ALLOC
> +# CHECK-NEXT:    SHF_EXECINSTR
> +# CHECK-NEXT:  ]
> +
> +## Check flags are the same if we omit empty synthetic section in script.
> +# RUN: echo "SECTIONS {              \
> +# RUN:         .foo : { *(.foo) }    \
> +# RUN:         .bar : { BYTE(0x11) }}" > %t.script
> +# RUN: ld.lld -o %t --script %t.script %t.o
> +# RUN: llvm-readobj -s %t | FileCheck %s
> +
> +.section .foo,"ax"
> +.quad 0
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