[glibc/release/2.36/master] powerpc: Fix ld.so address determination for PCREL mode (bug 31640)

[Florian Weimer <fw@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=78ad1b1b0d42b95c2c75463dc413bfd162a778e8

commit 78ad1b1b0d42b95c2c75463dc413bfd162a778e8
Author: Florian Weimer <fweimer@redhat.com>
Date:   Sun Apr 14 08:24:51 2024 +0200

    powerpc: Fix ld.so address determination for PCREL mode (bug 31640)
    
    This seems to have stopped working with some GCC 14 versions,
    which clobber r2.  With other compilers, the kernel-provided
    r2 value is still available at this point.
    
    Reviewed-by: Peter Bergner <bergner@linux.ibm.com>
    (cherry picked from commit 14e56bd4ce15ac2d1cc43f762eb2e6b83fec1afe)

Diff:
---
 sysdeps/powerpc/powerpc64/dl-machine.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/sysdeps/powerpc/powerpc64/dl-machine.h b/sysdeps/powerpc/powerpc64/dl-machine.h
index bb0ccd0811..3868bcc2f7 100644
--- a/sysdeps/powerpc/powerpc64/dl-machine.h
+++ b/sysdeps/powerpc/powerpc64/dl-machine.h
@@ -79,6 +79,7 @@ elf_host_tolerates_class (const Elf64_Ehdr *ehdr)
 static inline Elf64_Addr
 elf_machine_load_address (void) __attribute__ ((const));
 
+#ifndef __PCREL__
 static inline Elf64_Addr
 elf_machine_load_address (void)
 {
@@ -106,6 +107,24 @@ elf_machine_dynamic (void)
   /* Then subtract off the load address offset.  */
   return runtime_dynamic - elf_machine_load_address() ;
 }
+#else /* __PCREL__ */
+/* In PCREL mode, r2 may have been clobbered.  Rely on relative
+   relocations instead.  */
+
+static inline ElfW(Addr)
+elf_machine_load_address (void)
+{
+  extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
+  return (ElfW(Addr)) &__ehdr_start;
+}
+
+static inline ElfW(Addr)
+elf_machine_dynamic (void)
+{
+  extern ElfW(Dyn) _DYNAMIC[] attribute_hidden;
+  return (ElfW(Addr)) _DYNAMIC - elf_machine_load_address ();
+}
+#endif /* __PCREL__ */
 
 /* The PLT uses Elf64_Rela relocs.  */
 #define elf_machine_relplt elf_machine_rela