[glibc] m68k: Handle fewer relocations for RTLD_BOOTSTRAP (#BZ29071)

[Fangrui Song <maskray@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=a8e9b5b8079d18116ca69c9797e77804ecf2ee7e

commit a8e9b5b8079d18116ca69c9797e77804ecf2ee7e
Author: Fangrui Song <maskray@google.com>
Date:   Wed Apr 20 10:24:15 2022 -0700

    m68k: Handle fewer relocations for RTLD_BOOTSTRAP (#BZ29071)
    
    m68k is a non-PI_STATIC_AND_HIDDEN arch which uses a GOT relocation when
    loading the address of a jump table. The GOT load may be reordered
    before processing R_68K_RELATIVE relocations, leading to an
    unrelocated/incorrect jump table, which will cause a crash.
    
    The foolproof approach is to add an optimization barrier (e.g. calling
    an non-inlinable function after relative relocations are resolved). That
    is non-trivial given the current code structure, so just use the simple
    approach to avoid the jump table: handle only the essential reloctions
    for RTLD_BOOTSTRAP code.
    
    This is based on Andreas Schwab's patch and fixed ld.so crash on m68k.
    
    Reviewed-by: Adheemrval Zanella  <adhemerval.zanella@linaro.org>

Diff:
---
 sysdeps/m68k/dl-machine.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/sysdeps/m68k/dl-machine.h b/sysdeps/m68k/dl-machine.h
index c44ab055aa..bb51b4198c 100644
--- a/sysdeps/m68k/dl-machine.h
+++ b/sysdeps/m68k/dl-machine.h
@@ -234,6 +234,11 @@ elf_machine_rela (struct link_map *map, struct r_scope_elem *scope[],
 
       switch (r_type)
 	{
+	case R_68K_GLOB_DAT:
+	case R_68K_JMP_SLOT:
+	  *reloc_addr = value;
+	  break;
+#ifndef RTLD_BOOTSTRAP
 	case R_68K_COPY:
 	  if (sym == NULL)
 	    /* This can happen in trace mode if an object could not be
@@ -252,10 +257,6 @@ elf_machine_rela (struct link_map *map, struct r_scope_elem *scope[],
 	  memcpy (reloc_addr_arg, (void *) value,
 		  MIN (sym->st_size, refsym->st_size));
 	  break;
-	case R_68K_GLOB_DAT:
-	case R_68K_JMP_SLOT:
-	  *reloc_addr = value;
-	  break;
 	case R_68K_8:
 	  *(char *) reloc_addr = value + reloc->r_addend;
 	  break;
@@ -276,7 +277,6 @@ elf_machine_rela (struct link_map *map, struct r_scope_elem *scope[],
 	case R_68K_PC32:
 	  *reloc_addr = value + reloc->r_addend - (Elf32_Addr) reloc_addr;
 	  break;
-#ifndef RTLD_BOOTSTRAP
 	case R_68K_TLS_DTPMOD32:
 	  /* Get the information from the link map returned by the
 	     resolv function.  */
@@ -294,9 +294,9 @@ elf_machine_rela (struct link_map *map, struct r_scope_elem *scope[],
 	      *reloc_addr = TLS_TPREL_VALUE (sym_map, sym, reloc);
 	    }
 	  break;
-#endif /* !RTLD_BOOTSTRAP */
 	case R_68K_NONE:		/* Alright, Wilbur.  */
 	  break;
+#endif /* !RTLD_BOOTSTRAP */
 	default:
 	  _dl_reloc_bad_type (map, r_type, 0);
 	  break;