https://sourceware.org/bugzilla/show_bug.cgi?id=25599
Bug ID: 25599
Summary: gas generates invalid PCREL60B relocation offset with
brl.call
Product: binutils
Version: 2.32
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: gas
Assignee: unassigned at sourceware dot org
Reporter: peter.bisroev at groundlabs dot com
CC: dave.anglin at bell dot net
Target Milestone: ---
Created attachment 12322
--> https://sourceware.org/bugzilla/attachment.cgi?id=12322&action=edit
Code and binaries that display this bug.
Hi Everyone,
While attempting to help bootstrap a recent version of gcc on HP-UX IA-64
platform (GCC bug 61577 comments 202, 203 and 204), we have hit a PCREL60B
reloc related issue.
The following tools were used:
- HP-UX B.11.31 (IA-64)
- GCC 4.7.4
- Binutils 2.32 (but this happens with 2.34 as well)
- 92453-07 linker ld HP Itanium(R) B.12.65 IPF/IPF
In the attachment binutils-gas-PCREL60B-bug.tgz you will find all the code as
well as binaries used to trigger and demonstrate this issue. The source
main-brl.s was generated by taking the output of compiling main.c with
-save-temps option and changing br.call to brl.call, this source is presented
below:
------------------------------
.file "main.c"
.pred.safe_across_calls p1-p5,p16-p63
.section .text, "ax", "progbits"
.align 16
.global main#
.type main#, @function
.proc main#
main:
.prologue 14, 32
.save ar.pfs, r33
alloc r33 = ar.pfs, 0, 4, 0, 0
.vframe r34
mov r34 = r12
.save rp, r32
mov r32 = b0
mov r35 = r1
.body
;;
brl.call.sptk.many b0 = hello#
mov r1 = r35
mov r14 = r0
;;
mov r8 = r14
mov ar.pfs = r33
mov b0 = r32
.restore sp
mov r12 = r34
br.ret.sptk.many b0
;;
.endp main#
.global hello#
.type hello#, @function
.ident "GCC: (GNU) 4.7.4"
------------------------------
When assembling main-brl.s we get the expected PCREL60B relocation but at the
wrong offset (0x21 instead of 0x22):
------------------------------
20: 04 00 00 00 01 00 [MLX] nop.m 0x0
21: PCREL60B hello
26: 00 00 00 00 00 00 brl.call.sptk.many b0=20 <main+0x20>
------------------------------
If we now link this object into the final executable HP's linker clobbers the
nop.m at 0x20 due to the wrong reloc offset as shown below:
------------------------------
4000930: 04 00 00 00 00 00 [MLX] break.m 0x0
4000936: 00 30 00 00 00 00 brl.call.sptk.many
b0=4000930 <_end+0xc3ff08f0>
400093c: 08 00 00 d0
------------------------------
This seems to be the only issue here. To verify I checked the 60 bit immediate
that gets encoded and it seems to be correct. I have also manually patched
main-brl.o to change the reloc offset from 0x21 to 0x22 and relinked as shown
below:
------------------------------
# objdump -rd main-brl-patched.o
20: 04 00 00 00 01 00 [MLX] nop.m 0x0
22: PCREL60B hello
26: 00 00 00 00 00 00 brl.call.sptk.many b0=20 <main+0x20>
# objdump -rd hello-brl-patched
4000930: 04 00 00 00 01 00 [MLX] nop.m 0x0
4000936: 00 00 00 00 00 00 brl.call.sptk.many
b0=4000990 <hello>
400093c: 68 00 00 d0
------------------------------
As can be seen above the relocation is now correct and the executable works as
expected.
Please let me know if further info is required.
Thank you!
--peter
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