Most PIE binaries generated on MIPS are broken. Here is a small testcase to
demonstrate the problem:
/* compile with cc -pie -fPIE -o fpie fpie.c */
#include <stdio.h>
#include <string.h>
int val0 = 3;
int val1 = 4;
int *vals[2] = {
&val0,
&val1
};
int main(void)
{
printf("val0 is %i\n", *vals[0]);
printf("val1 is %i\n", *vals[1]);
return 0;/* compile with cc -pie -fPIE -o fpie fpie.c */
#include <stdio.h>
#include <string.h>
int val0 = 3;
int val1 = 4;
int *vals[2] = {
&val0,
&val1
};
int main(void)
{
printf("val0 is %i\n", *vals[0]);
printf("val1 is %i\n", *vals[1]);
return 0;
}
Note that for an unknown reason, gcc 4.3 does not generate a pie binary
with -pie (not specific to MIPS), so you may want to try it with gcc 4.1.
Such a code crashes on startup during the relocation phase. This is due to a
wrong ELF header. Compared to a working binutils, val0 and val1 do not appear
in '.dynsym'. As a consequence '.rel.dyn' is filled with bad entries, causing
the crash:
Relocation section '.rel.dyn' at offset 0x594 contains 5 entries:
Offset Info Type Sym.Value Sym. Name
00000000 00000000 R_MIPS_NONE
00010ab0 00000003 R_MIPS_REL32
00010ab4 00000003 R_MIPS_REL32
00010ad0 ffffff03 R_MIPS_REL32 bad symbol index: 00ffffff
00010ad4 ffffff03 R_MIPS_REL32 bad symbol index: 00ffffff
Manually editing '.rel.dyn' with an hex editor to point the entries to another
symbol cause the crash to disappear. Of course the value is then wrong.
--
Summary: ld generate broken PIE binaries on MIPS
Product: binutils
Version: 2.20
Status: NEW
Severity: normal
Priority: P2
Component: ld
AssignedTo: unassigned at sources dot redhat dot com
ReportedBy: aurelien at aurel32 dot net
CC: bug-binutils at gnu dot org
GCC build triplet: mipsel-unknown-linux-gnu
GCC host triplet: mipsel-unknown-linux-gnu
GCC target triplet: mipsel-unknown-linux-gnu
http://sourceware.org/bugzilla/show_bug.cgi?id=10858
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