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Build: Pass "-z separate-code" to linker

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This tells the linker to not combine read-only data and executable code,
instead favoring multiple PT_LOAD headers with more precise permissions.

This greatly reduces the amount of executable pages in all our programs
and libraries.

/usr/lib/libjs.so before:

  Type           Offset   VirtAddr   PhysAddr   FileSiz  MemSiz   Flg Align
  LOAD           0x000000 0x00000000 0x00000000 0x2fc77c 0x2fc77c R E 0x1000
  LOAD           0x2fc900 0x002fd900 0x002fd900 0x0c708  0x0dd1c  RW  0x1000

/usr/lib/libjs.so after:

  Type           Offset   VirtAddr   PhysAddr   FileSiz  MemSiz   Flg Align
  LOAD           0x000000 0x00000000 0x00000000 0x80e60  0x80e60  R   0x1000
  LOAD           0x081000 0x00081000 0x00081000 0x25f6c9 0x25f6c9 R E 0x1000
  LOAD           0x2e1000 0x002e1000 0x002e1000 0x1c27c  0x1c27c  R   0x1000
  LOAD           0x2fd900 0x002fe900 0x002fe900 0x0c708  0x0dd1c  RW  0x1000

As you can see, we go from 0x2fc77c bytes of executable memory down to
0x25f6c9 (a ~20% reduction!) The memory that was previous executable is
now simply read-only instead. :^)
This commit is contained in:
Andreas Kling 2021-08-31 16:08:11 +02:00
parent 5046a1fe38
commit fac0bbe739
1 changed files with 2 additions and 2 deletions
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4
CMakeLists.txt
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@ -217,8 +217,8 @@ endforeach()
set(CMAKE_INSTALL_NAME_TOOL "")
set(CMAKE_SHARED_LIBRARY_SUFFIX ".so")
set(CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS "-shared -Wl,--hash-style=gnu,-z,relro,-z,now,-z,noexecstack")
set(CMAKE_CXX_LINK_FLAGS "-Wl,--hash-style=gnu,-z,relro,-z,now,-z,noexecstack,-z,max-page-size=0x1000")
set(CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS "-shared -Wl,--hash-style=gnu,-z,relro,-z,now,-z,noexecstack,-z,separate-code")
set(CMAKE_CXX_LINK_FLAGS "-Wl,--hash-style=gnu,-z,relro,-z,now,-z,noexecstack,-z,max-page-size=0x1000,-z,separate-code")
# We disable it completely because it makes cmake very spammy.
# This will need to be revisited when the Loader supports RPATH/RUN_PATH.