When linking object files using the options --gc-sections and -relax
(MicroBlaze specific option that
removes superfluous "imm 0" instructions), the addresses for some labels are
miscalculated.
Apparently this problem is caused by removing the "imm 0" instructions without
changing the labels'
addresses accordingly (e.g., when 2 "imm 0" instructions are removed, the
address is off by 2
instructions). It seems this only occurs in files generated from assembler
source code. We did not
notice this behavior in linked object files compiled from C/C++ Code.
gcc/g++ by default passes -relax to ld when compiling for microblaze, so many
users may be unaware
of what causes that but.
The effect shows when using ld compiled from the current version out of cvs
(GNU ld (GNU Binutils)
2.20.51.20091211) as well as older versions (e.g., 2.16) distributed with
Xilinx EDK 10 and 11.
Code example:
Without using the -relax option, objdump shows the correct code:
00000050 <_myStart>:
50: 80000000 or r0, r0, r0
54: 80000000 or r0, r0, r0
58: b0000000 imm 0
5c: b9f40028 brlid r15, 40 // 84 <main>
60: b800000c bri 12 // 6c <_bla>
64: 80000000 or r0, r0, r0
68: b800ffe8 bri -24 // 50 <_TEXT_START_ADDR>
0000006c <_bla>:
6c: b8000000 bri 0 // 6c <_bla>
00000070 <_foobar>:
70: 32e0002a addik r23, r0, 42
74: 32e00017 addik r23, r0, 23
78: 80000000 or r0, r0, r0
Using both -relax and --gc-sections the objdump shows:
00000050 <_myStart>:
50: 80000000 or r0, r0, r0
54: 80000000 or r0, r0, r0
58: b9f40028 brlid r15, 40 // 80 <main>
5c: b8000010 bri 16 // 6c <_bla>
60: 80000000 or r0, r0, r0
64: b800ffec bri -20 // 50 <_TEXT_START_ADDR>
68: b8000004 bri 4 // 6c <_bla>
0000006c <_bla>:
6c: 32e0002a addik r23, r0, 42
00000070 <_foobar>:
70: 32e00017 addik r23, r0, 23
74: 80000000 or r0, r0, r0
Both labels _bla and _foobar are at the wrong address.
--
Summary: Incorrect address calculation for Microblaze assembler
code when using -relax and --gc-sections options
Product: binutils
Version: 2.20
Status: NEW
Severity: normal
Priority: P2
Component: ld
AssignedTo: unassigned at sources dot redhat dot com
ReportedBy: michael dot engel at tu-dortmund dot de
CC: bug-binutils at gnu dot org
GCC host triplet: i386-pc-linux-gnu
GCC target triplet: microblaze-unknown-none
http://sourceware.org/bugzilla/show_bug.cgi?id=11085
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