[Bug ld/19965] Copy relocation leads to change in read-only data

[amodra at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19965

--- Comment #4 from Alan Modra  ---
BTW, the testcase in comment #3 (and yours too!) show just how difficult it is
to fix this problem.  When the main program is *not* relro you don't have
anywhere to put the new .dynbss.ro or whatever you want to call the internal
linker generated section for read-only .dynbss variables.  You don't have a
.data.rel.ro in the main executable and can't tack them on to .rodata, because
then ld.so will segfault when applying the copy relocation..

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[Bug ld/19965] Copy relocation leads to change in read-only data

[amodra at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19965

Alan Modra  changed:

   What|Removed |Added

 CC||amodra at gmail dot com

--- Comment #3 from Alan Modra  ---
Here's a testcase that I think does not invoke any undefined behaviour, and
shows various inconsistencies with protected variables and copy relocs. 
Depending on the version of gcc (and glibc!) you may see  != x or no
segfault.
Compile protmain with -fPIC to see correct behaviour.

cat > prot.h <<\EOF
extern void *x;
extern void aprint (void);
extern void boom (void);
EOF
cat > prota.c <<\EOF
#include "prot.h"
void __attribute__ ((visibility ("protected"), section(".data.rel.ro")))
  *x = 
void aprint (void) { __builtin_printf ("A:  = %p, x = %p\n", , x); }
EOF
cat > protb.c <<\EOF
#include "prot.h"
void boom (void) { x = 0; }
EOF
cat > protmain.c <<\EOF
#include "prot.h"
int
main (void)
{
  __builtin_printf ("main:  = %p, x = %p\n", , x);
  aprint ();
  boom ();
  return 0;
}
EOF
gcc -O2 -fPIC -shared -o liba.so prota.c protb.c -Wl,-z,relro
gcc -O2 -o protmain protmain.c -L. -la -Wl,-rpath,.
./protmain

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[Bug gold/19891] arm: The order of IFUNC (R_ARM_IRELATIVE and R_ARM_JUMP_SLOT) relocations is incorrect

[shenhan at google dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19891

Han Shen  changed:

   What|Removed |Added

 Status|ASSIGNED|RESOLVED
 Resolution|--- |WONTFIX

--- Comment #3 from Han Shen  ---
Discussed with reporter. This is not caused by the order of R_ARM_IRELATIVE.
I'll mark this as WONTFIX.

Thanks,
Han

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[Bug binutils/19722] [libopcodes] [Aarch64] Undefined SIMD instruction not marked undefined

[njholcomb at wi dot rr.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19722

--- Comment #4 from njholcomb at wi dot rr.com ---
This may not be a valid output from the libopcodes disassembler, but there are
a lot of tools out there, and not all of them may produce expected
instructions. People can also edit binaries themselves, placing arbitrary
bytes. Furthermore, this instruction executes without any signal on at least
one chip, where it both loads a word into x6 and applies the post-fix after
loading in the word, a completely unspecified (though maybe predictable)
behavior. Identifying invalid instructions like this is essential to debugging
code that behaves unexpectedly.

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[Bug ld/19965] Copy relocation leads to change in read-only data

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19965

--- Comment #2 from H.J. Lu  ---
(In reply to Andreas Schwab from comment #1)
> And how is that a bug?  The program invokes undefined behavior.

Linker should generate copy relocation against read-only symbol
in .data.rel.ro section, instead of .bss section, so that the
copy of read-only symbol is also read-only after relocation at
run-time.

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[Bug ld/19965] Copy relocation leads to change in read-only data

[sch...@linux-m68k.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=19965

--- Comment #1 from Andreas Schwab  ---
And how is that a bug?  The program invokes undefined behavior.

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[Bug binutils/19661] [libopcodes] [x86] Lock prefixes are allowed even when they SIGILL

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19661

H.J. Lu  changed:

   What|Removed |Added

 Status|WAITING |RESOLVED
 Resolution|--- |WONTFIX

--- Comment #3 from H.J. Lu  ---
(In reply to njholcomb from comment #2)
> Created attachment 9202 [details]
> File displays locking without a memory operand.
> 
> objdump -d lock_no_mem.o
> 
> lock_no_mem.o: file format elf64-x86-64
> 
> 
> Disassembly of section .text:
> 
>  :
>0:   55  push   %rbp
>1:   48 89 e5mov%rsp,%rbp
>4:   f0 b7 9flock mov $0x9f,%bh
>7:   96  xchg   %eax,%esi
>8:   00 00   add%al,(%rax)
>a:   00 b8 00 00 00 00   add%bh,0x0(%rax)
>   10:   5d  pop%rbp
>   11:   c3  retq

It looks OK to me.  You get UD because LOCK prefix is used on non-memory
operand:

(gdb) disass
Dump of assembler code for function main:
   0x00400488 <+0>: push   %rbp
   0x00400489 <+1>: mov%rsp,%rbp
=> 0x0040048c <+4>: lock mov $0x9f,%bh
   0x0040048f <+7>: xchg   %eax,%esi
   0x00400490 <+8>: add%al,(%rax)
   0x00400492 <+10>:add%bh,0x0(%rax)
   0x00400498 <+16>:pop%rbp
   0x00400499 <+17>:retq   
End of assembler dump.
(gdb)

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[Bug binutils/19659] [libopcodes] Segmentation fault on print_insn_i386

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19659

H.J. Lu  changed:

   What|Removed |Added

 Status|WAITING |RESOLVED
 Resolution|--- |WORKSFORME

--- Comment #3 from H.J. Lu  ---
./objdump -dwr x.o

x.o: file format elf64-x86-64


Disassembly of section .text:

 :
   0:   55  push   %rbp
   1:   48 89 e5mov%rsp,%rbp
   4:   8f  (bad)  
   5:   eb 5c   jmp63 
   7:   ec  in (%dx),%al
   8:   00 00   add%al,(%rax)
   a:   00 b8 00 00 00 00   add%bh,0x0(%rax)
  10:   5d  pop%rbp
  11:   c3  retq   
[hjl@gnu-6 pr19659]$

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[Bug binutils/19660] [libopcodes] [x86] REP prefixes shown incorrectly

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19660

--- Comment #3 from H.J. Lu  ---
(In reply to njholcomb from comment #2)
> Created attachment 9201 [details]
> Shows rep prefixes on non-string instructions

I got

 :
   0:   55  push   %rbp
   1:   48 89 e5mov%rsp,%rbp
   4:   f3 e0 58repz loopne 5f 
   7:   f2 00 00repnz add %al,(%rax)
   a:   00 b8 00 00 00 00   add%bh,0x0(%rax)
  10:   5d  pop%rbp
  11:   c3  retq   

repz is nop before loopne.  repnz is UD before add:

Program received signal SIGSEGV, Segmentation fault.
0x0040048f in main ()
(gdb) disass
Dump of assembler code for function main:
   0x00400488 <+0>: push   %rbp
   0x00400489 <+1>: mov%rsp,%rbp
   0x0040048c <+4>: repz loopne 0x4004e7 <__libc_csu_init+71>
=> 0x0040048f <+7>: repnz add %al,(%rax)
   0x00400492 <+10>:add%bh,0x0(%rax)
   0x00400498 <+16>:pop%rbp
   0x00400499 <+17>:retq   
End of assembler dump.
(gdb) 

Disassembler output looks OK to me.

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[Bug ld/19965] New: Copy relocation leads to change in read-only data

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19965

Bug ID: 19965
   Summary: Copy relocation leads to change in read-only data
   Product: binutils
   Version: 2.27 (HEAD)
Status: NEW
  Severity: normal
  Priority: P2
 Component: ld
  Assignee: unassigned at sourceware dot org
  Reporter: hjl.tools at gmail dot com
  Target Milestone: ---
Target: x86

[hjl@gnu-6 relro-9]$ cat x.c
int const p1[1] = { -1 };
[hjl@gnu-6 relro-9]$ cat foo.c
#include 

extern int const p1[1];

void
foo (void)
{
  if (p1[0] != -1)
abort ();
}
[hjl@gnu-6 relro-9]$ cat m.c
#include 

extern void foo (void);

extern int p1[1];

int
main ()
{
  foo ();
  printf ("%d\n", p1[0]);
  p1[0] = 0;
  foo ();
  return 0;
}
[hjl@gnu-6 relro-9]$ make
gcc -O2 -g   -c -o m.o m.c
gcc -O2 -g -fPIC   -c -o x.o x.c
gcc -O2 -g -fPIC   -c -o foo.o foo.c
ld -shared --gc-sections -z relro -o libx.so x.o foo.o
gcc -o x -O2 -g m.o libx.so -Wl,-R,.
./x
-1
Makefile:10: recipe for target 'all' failed
make: *** [all] Aborted
[hjl@gnu-6 relro-9]$

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[Bug binutils/19661] [libopcodes] [x86] Lock prefixes are allowed even when they SIGILL

[njholcomb at wi dot rr.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19661

--- Comment #2 from njholcomb at wi dot rr.com ---
Created attachment 9202
  --> https://sourceware.org/bugzilla/attachment.cgi?id=9202=edit
File displays locking without a memory operand.

objdump -d lock_no_mem.o

lock_no_mem.o: file format elf64-x86-64


Disassembly of section .text:

 :
   0:   55  push   %rbp
   1:   48 89 e5mov%rsp,%rbp
   4:   f0 b7 9flock mov $0x9f,%bh
   7:   96  xchg   %eax,%esi
   8:   00 00   add%al,(%rax)
   a:   00 b8 00 00 00 00   add%bh,0x0(%rax)
  10:   5d  pop%rbp
  11:   c3  retq

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[Bug binutils/19660] [libopcodes] [x86] REP prefixes shown incorrectly

[njholcomb at wi dot rr.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19660

--- Comment #2 from njholcomb at wi dot rr.com ---
Created attachment 9201
  --> https://sourceware.org/bugzilla/attachment.cgi?id=9201=edit
Shows rep prefixes on non-string instructions

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[Bug binutils/19659] [libopcodes] Segmentation fault on print_insn_i386

[njholcomb at wi dot rr.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19659

--- Comment #2 from njholcomb at wi dot rr.com ---
Created attachment 9200
  --> https://sourceware.org/bugzilla/attachment.cgi?id=9200=edit
File causes Abort by objdump

This file contains bytes that objdump fails to decode using "objdump -d"
because it aborts during decoding.

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