回复: [PATCH v4 04/13] LoongArch: ABI Implementation

[<caiyinyu@loongson.cn>]

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发件人: Fangrui Song
发送时间: 2022年5月9日 16:24
收件人: caiyinyu
抄送: libc-alpha@sourceware.org; xuchenghua@loongson.cn; joseph_myers@mentor.com
主题: Re: [PATCH v4 04/13] LoongArch: ABI Implementation

>+/* Runtime address of .got */
>+#define _GLOBAL_OFFSET_TABLE_ \
>+  ({ \
>+    ElfW (Addr) * r; \
>+    asm("la.pcrel %0, _GLOBAL_OFFSET_TABLE_" : "=r"(r)); \
>+    r; \
>+  })
>+
>+/* Return the link-time address of _DYNAMIC.  */
>+static inline ElfW (Addr) elf_machine_dynamic (void)
>+{
>+  return _GLOBAL_OFFSET_TABLE_[0];
>+}

_GLOBAL_OFFSET_TABLE_[0] == link_time_dynamic is not recommended.
See
https://maskray.me/blog/2021-09-05-build-glibc-with-lld#global_offset_table_0
aarch64/riscv/x86_64/etc have been updated to use the preferred
approach.

Fixed.


diff --git a/sysdeps/loongarch/dl-machine.h b/sysdeps/loongarch/dl-machine.h
index f902410213..361f7555f9 100644
--- a/sysdeps/loongarch/dl-machine.h
+++ b/sysdeps/loongarch/dl-machine.h
@@ -70,28 +70,18 @@ elf_machine_matches_host (const ElfW (Ehdr) * ehdr)
   return 1;
 }

-/* Runtime address of .got */
-#define _GLOBAL_OFFSET_TABLE_ \
-  ({ \
-    ElfW (Addr) * r; \
-    asm("la.pcrel %0, _GLOBAL_OFFSET_TABLE_" : "=r"(r)); \
-    r; \
-  })
-
-/* Return the link-time address of _DYNAMIC.  */
-static inline ElfW (Addr) elf_machine_dynamic (void)
+/* Return the run-time load address of the shared object.  */
+static inline ElfW (Addr) elf_machine_load_address (void)
 {
-  return _GLOBAL_OFFSET_TABLE_[0];
+  extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
+  return (ElfW(Addr)) &__ehdr_start;
 }

-/* Return the run-time load address of the shared object.  */
-static inline ElfW (Addr) elf_machine_load_address (void)
+/* Return the link-time address of _DYNAMIC.  */
+static inline ElfW (Addr) elf_machine_dynamic (void)
 {
-  ElfW (Addr) got_linktime_addr;
-  asm("la.got %0, _GLOBAL_OFFSET_TABLE_"
-      /* Link-time address in GOT entry before runtime relocation */
-      : "=r"(got_linktime_addr));
-  return (ElfW (Addr)) _GLOBAL_OFFSET_TABLE_ - got_linktime_addr;
+  extern ElfW(Dyn) _DYNAMIC[] attribute_hidden;
+  return (ElfW(Addr)) _DYNAMIC - elf_machine_load_address ();
 }





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