[PATCH 2/3] Revert "[AArch64][BZ #17711] Fix extern protected data handling"

[Fangrui Song <maskray@google.com>]

This reverts commit 0910702c4d2cf9e8302b35c9519548726e1ac489.

Say both a.so and b.so define protected var and the executable copy
relocates var. ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA has strange
semantics: a.so accesses the copy in the executable while b.so accesses
its own. This behavior requires that (a) the compiler emits
GOT-generating relocations (b) the linker produces GLOB_DAT instead of
RELATIVE.

Without the ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA code, b.so's GLOB_DAT
will bind to the executable (normal behavior).

For aarch64 it makes sense to restore the original behavior and don't
pay the ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA cost. The behavior is very
unlikely used by anyone.

* Clang code generation treats STV_PROTECTED the same way as STV_HIDDEN:
  no GOT-generating relocation in the first place.
* gold and lld reject copy relocation on a STV_PROTECTED symbol.
* Nowadays -fpie/-fpic modes are popular. GCC/Clang's codegen uses
  GOT-generating relocation when accessing an default visibility
  external symbol which avoids copy relocation.
---
 sysdeps/aarch64/dl-machine.h | 13 ++++++-------
 sysdeps/aarch64/dl-sysdep.h  |  2 --
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/sysdeps/aarch64/dl-machine.h b/sysdeps/aarch64/dl-machine.h
index b40050a981..530952a736 100644
--- a/sysdeps/aarch64/dl-machine.h
+++ b/sysdeps/aarch64/dl-machine.h
@@ -182,13 +182,12 @@ _dl_start_user:								\n\
 ");
 
 #define elf_machine_type_class(type)					\
-  ((((type) == AARCH64_R(JUMP_SLOT)					\
-     || (type) == AARCH64_R(TLS_DTPMOD)					\
-     || (type) == AARCH64_R(TLS_DTPREL)					\
-     || (type) == AARCH64_R(TLS_TPREL)					\
-     || (type) == AARCH64_R(TLSDESC)) * ELF_RTYPE_CLASS_PLT)		\
-   | (((type) == AARCH64_R(COPY)) * ELF_RTYPE_CLASS_COPY)		\
-   | (((type) == AARCH64_R(GLOB_DAT)) * ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA))
+  ((((type) == R_AARCH64_JUMP_SLOT ||					\
+     (type) == R_AARCH64_TLS_DTPMOD ||					\
+     (type) == R_AARCH64_TLS_DTPREL ||					\
+     (type) == R_AARCH64_TLS_TPREL ||					\
+     (type) == R_AARCH64_TLSDESC) * ELF_RTYPE_CLASS_PLT)		\
+   | (((type) == R_AARCH64_COPY) * ELF_RTYPE_CLASS_COPY))
 
 #define ELF_MACHINE_JMP_SLOT	AARCH64_R(JUMP_SLOT)
 
diff --git a/sysdeps/aarch64/dl-sysdep.h b/sysdeps/aarch64/dl-sysdep.h
index 667786671c..ac69f414f3 100644
--- a/sysdeps/aarch64/dl-sysdep.h
+++ b/sysdeps/aarch64/dl-sysdep.h
@@ -21,5 +21,3 @@
 /* _dl_argv cannot be attribute_relro, because _dl_start_user
    might write into it after _dl_start returns.  */
 #define DL_ARGV_NOT_RELRO 1
-
-#define DL_EXTERN_PROTECTED_DATA
-- 
2.36.0.464.gb9c8b46e94-goog