[glibc/ibm/2.30/master] i386: Use comdat instead of .gnu.linkonce for i386 setup pic register (BZ #20543)

[glibc/ibm/2.30/master] i386: Use comdat instead of .gnu.linkonce for i386 setup pic register (BZ #20543)

[Tulio Magno Quites Machado Filho]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=1ce16683d9efa1cc611ed4632645e16742699d10

commit 1ce16683d9efa1cc611ed4632645e16742699d10
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Fri Feb 28 10:46:14 2020 -0300

    i386: Use comdat instead of .gnu.linkonce for i386 setup pic register (BZ #20543)
    
    GCC has moved from using .gnu.linkonce for i386 setup pic register with
    minimum current version (as for binutils minimum binutils that support
    comdat).
    
    Trying to pinpoint when binutils has added comdat support for i686, it
    seems it was around 2004 [1].  I also checking with some ancient
    binutils older than 2.16 I see:
    
    test.o: In function `__x86.get_pc_thunk.bx':
    test.o(.text.__x86.get_pc_thunk.bx+0x0): multiple definition of `__x86.get_pc_thunk.bx'
    /usr/lib/gcc/x86_64-linux-gnu/5/../../../i386-linux-gnu/crti.o(.gnu.linkonce.t.__x86.get_pc_thunk.bx+0x0): first defined here
    
    Which seems that such version can not handle either comdat at all or
    a mix of linkonce and comdat.  For binutils 2.16.1 I am getting a
    different issue trying to link a binary with and more recent
    ctri.o (unrecognized relocation (0x2b) in section `.init', which is
    R_386_GOT32X and old binutils won't generate it anyway).
    
    So I think that either unlikely someone will use an older binutils than
    the one used to glibc and even this scenario may fail with some issue
    as the R_386_GOT32X.  Also, 2.16.1 is quite old and not really supported
    (glibc itself required 2.25).
    
    Checked on i686-linux-gnu.
    
    [1] https://gcc.gnu.org/ml/gcc/2004-05/msg00030.html
    
    (cherry picked from commit 35200fd3892f6caf867bf89bc8048e553906af28)

Diff:
---
 NEWS                  | 1 +
 sysdeps/i386/sysdep.h | 5 +++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/NEWS b/NEWS
index d966688a56..76cfbcaa16 100644
--- a/NEWS
+++ b/NEWS
@@ -24,6 +24,7 @@ CVE-2020-1752: A use-after-free vulnerability in the glob function when
 
 The following bugs are resolved with this release:
 
+  [20543] Please move from .gnu.linkonce to comdat
   [23518] login: Remove utmp backend jump tables
   [24682] localedata: zh_CN first weekday should be Monday per GB/T
     7408-2005
diff --git a/sysdeps/i386/sysdep.h b/sysdeps/i386/sysdep.h
index 749b55b077..eee6d586c1 100644
--- a/sysdeps/i386/sysdep.h
+++ b/sysdeps/i386/sysdep.h
@@ -61,7 +61,7 @@ lose: SYSCALL_PIC_SETUP							      \
 
 # define SETUP_PIC_REG(reg) \
   .ifndef GET_PC_THUNK(reg);						      \
-  .section .gnu.linkonce.t.GET_PC_THUNK(reg),"ax",@progbits;		      \
+  .section .text.GET_PC_THUNK(reg),"axG",@progbits,GET_PC_THUNK(reg),comdat;  \
   .globl GET_PC_THUNK(reg);						      \
   .hidden GET_PC_THUNK(reg);						      \
   .p2align 4;								      \
@@ -97,7 +97,8 @@ GET_PC_THUNK(reg):							      \
 
 # define SETUP_PIC_REG_STR(reg)						\
   ".ifndef " GET_PC_THUNK_STR (reg) "\n"				\
-  ".section .gnu.linkonce.t." GET_PC_THUNK_STR (reg) ",\"ax\",@progbits\n" \
+  ".section .text." GET_PC_THUNK_STR (reg) ",\"axG\",@progbits,"	\
+    GET_PC_THUNK_STR (reg) ",comdat\n"					\
   ".globl " GET_PC_THUNK_STR (reg) "\n"					\
   ".hidden " GET_PC_THUNK_STR (reg) "\n"				\
   ".p2align 4\n"							\