http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54821
Bug #: 54821
Summary: Microblaze: Position independent code for byte access
is incorrect.
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: middle-end
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: qb...@sarine.nl
When enabling position independent code gcc generates incorrect assembly for
byte access. Works fine when generating word (32bit) loads/writes.
e.g.
When doing a word load results in the following correct assembly:
lwi r3, r20, 20 # load the address at .got.plt
+ 20 (address of a variable in the .got section)
lwi r4, r3, 0 # load the value of the
variable in r4
However when doing byte load:
imm 4
lbui r3, r20, 23884 # load the value of the variable in
r3. The address used is r20 + 0x45d4c.
There are 2 things going wrong..
1.) It tries to load the r20 + the absolute offset of the variable.
2.) It should first load the address (from the got) then load the value from
that address
I would expect something like:
lwi r3, r20, 16
lbui r4, r3, 0
A similar things goes wrong for half word access.
This problem can be reproduced with GCC 4.1.2 (from xilinx) up to 4.7.2 (When
looking in the object files, generating elf files fails as of bug #54819)
A script to build the cross-compiler can be found here:
https://github.com/DaveDavenport/CrossCompilerGCCScript/blob/master/gcc_cross_compiler.sh
C code that shows the issue:
char temp = 3;
int temp2 = 12;
short int temp4 =13;
void main()
{
int a = temp+ temp2+temp4;
}
Output generated for this: (by 4.1.2)
000001b0 <main>:
1b0: 3021fff0 addik r1, r1, -16
1b4: fa610008 swi r19, r1, 8
1b8: fa81000c swi r20, r1, 12
1bc: 12610000 addk r19, r1, r0
1c0: e0740444 lbui r3, r20, 1092
1c4: 90630060 sext8 r3, r3
1c8: 10830000 addk r4, r3, r0
1cc: b0000000 imm 0
1d0: e874000c lwi r3, r20, 12
1d4: e8630000 lwi r3, r3, 0
1d8: 10841800 addk r4, r4, r3
1dc: e474044c lhui r3, r20, 1100
1e0: 90630061 sext16 r3, r3
1e4: 10641800 addk r3, r4, r3
1e8: f8730004 swi r3, r19, 4
1ec: 10330000 addk r1, r19, r0
1f0: ea610008 lwi r19, r1, 8
1f4: ea81000c lwi r20, r1, 12
1f8: 30210010 addik r1, r1, 16
1fc: b60f0008 rtsd r15, 8
200: 80000000 or r0, r0, r0
Only the load word is done correctly.
