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hoyosjs merged 1 commit into from
Jul 7, 2022
Merged

Improve objcopy detection #71742

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15 changes: 9 additions & 6 deletions eng/native/configuretools.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -51,13 +51,16 @@ if(NOT WIN32 AND NOT CLR_CMAKE_TARGET_BROWSER)
locate_toolchain_exec(objdump CMAKE_OBJDUMP)
locate_toolchain_exec(objcopy CMAKE_OBJCOPY)

execute_process(
COMMAND ${CMAKE_OBJCOPY} --help
OUTPUT_VARIABLE OBJCOPY_HELP_OUTPUT
)

if(CLR_CMAKE_TARGET_ANDROID)
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@am11 am11 Jul 6, 2022

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This block was unused.

set(TOOLSET_PREFIX ${ANDROID_TOOLCHAIN_PREFIX})
elseif(CMAKE_CROSSCOMPILING AND NOT DEFINED CLR_CROSS_COMPONENTS_BUILD AND
CMAKE_SYSTEM_PROCESSOR MATCHES "^(armv8l|armv7l|armv6l|aarch64|arm|s390x|ppc64le)$")
set(TOOLSET_PREFIX "${TOOLCHAIN}-")
endif()
# if llvm-objcopy does not support --only-keep-debug argument, try to locate binutils' objcopy
if (CMAKE_C_COMPILER_ID MATCHES "Clang" AND NOT "${OBJCOPY_HELP_OUTPUT}" MATCHES "--only-keep-debug")
set(TOOLSET_PREFIX "")
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@hoyosjs hoyosjs Jul 7, 2022

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llvm also has a only-keep-debug flag, only with one dash though. Any reason to favor binutils over llvm's and just adjusting the flag?

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@am11 am11 Jul 7, 2022

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My test was:

$ docker run -it ubuntu:18.04

# inside the container, install different versions
$ apt update; apt install -y llvm-6 llvm-7 llvm-8 llvm-9 llvm-10

# test for only-keep-debug

# v6 - desired argument is unsupported
$ llvm-objcopy-6.0 --help | grep only-keep-debug         
# nothing found

# v7 - supported with single hyphen but is a no-op
$ llvm-objcopy-7 --help | grep only-keep-debug
  -only-keep-debug        Currently ignored. Only for compaitability with GNU objcopy.

# v8 - same as v7
$ llvm-objcopy-8 --help | grep only-keep-debug
  -only-keep-debug        Currently ignored. Only for compatibility with GNU objcopy.

# v9 - supported with double hyphen
$ llvm-objcopy-9 --help | grep only-keep-debug
  --only-keep-debug       Clear sections that would not be stripped by --strip-debug. Currently only implemented for COFF.

# v10 - same as v9
$ llvm-objcopy-10 --help | grep only-keep-debug
  --only-keep-debug       Produce a debug file as the output that only preserves contents of sections useful for debugging purposes

We want only-keep-debug for consistent output; avoid binary size bloat and avoid repeating issues like #49081. Therefore, we fallback to binutils' objcopy when llvm-objcopy is incapable of stripping the symbols. As you can see above, versions of llvm-objcopy which support double hyphened argument provide non-nop functionality.

locate_toolchain_exec(objcopy CMAKE_OBJCOPY)
endif ()

endif()
endif()
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