https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61577
--- Comment #192 from Peter Bisroev <peter.bisroev at groundlabs dot com> ---
(In reply to dave.anglin from comment #191)
> On 2020-02-19 9:50 p.m., peter.bisroev at groundlabs dot com wrote:
> The problem seems to be that HP ld doesn't handle the PCREL21B relocation
> correctly when it refers
> to a weak function (i.e., it doesn't direct the call through the PLT). At
> the same time, weak references
> don't seem to work with aCC.
>
> As far as I can tell, the PCREL21B is generated by gas in
> gas/config/tc-ia64.c at line 5919. You could try
> changing it to PCREL21BI to see if that helps (run binutils testsuite before
> installing) but the change doesn't
> seem correct. We might need to generate a 32-bit branch to weak functions
> in gcc.
Hi Dave, thanks for the hint! I have patched by binutils 2.32 as shown in the
diff below.
------------------------------
*** ./gas/config/tc-ia64.c.orig Fri Feb 21 23:52:59 2020
--- ./gas/config/tc-ia64.c Fri Feb 21 23:54:04 2020
***************
*** 5919,5925 ****
else if (opnd == IA64_OPND_TGT25b)
fix->code = BFD_RELOC_IA64_PCREL21M;
else if (opnd == IA64_OPND_TGT25c)
! fix->code = BFD_RELOC_IA64_PCREL21B;
else if (opnd == IA64_OPND_TGT64)
fix->code = BFD_RELOC_IA64_PCREL60B;
else
--- 5919,5925 ----
else if (opnd == IA64_OPND_TGT25b)
fix->code = BFD_RELOC_IA64_PCREL21M;
else if (opnd == IA64_OPND_TGT25c)
! fix->code = BFD_RELOC_IA64_PCREL21BI;
else if (opnd == IA64_OPND_TGT64)
fix->code = BFD_RELOC_IA64_PCREL60B;
else
------------------------------
After recompiling binutils gas failed only two more unit tests than before:
------------------------------
FAIL: ia64 tls
FAIL: ia64 relocations
------------------------------
After looking at both of these I guess it is expected as both of them expect
PCREL21B instead of PCREL21BI.
I have then attempted to recompile gcc 4.7.4 with this patched gas.
Unfortunately that fails during linking when xgcc tries to build
hpux64/libgcc_s.so.0.tmp in 64bit mode during stage 1. An example of an error
is:
------------------------------
ld: Unsatisfied symbol"calloc" in file "emutls_s.o": Expect to be defined in
the load module.
------------------------------
Taking a quick look at emutls_s.o I can see the expected reallocation
------------------------------
$ readelf -r ./ia64-hp-hpux11.31/hpux64/libgcc/emutls_s.o | grep calloc
0000000004d2 002200000079 R_IA64_PCREL21BI 0000000000000000 calloc + 0
------------------------------
But I have not dug dipper as to why the HP linker is unhappy there. Please let
me know if you want me to do so.
> It would be useful to find out why weak doesn't work with aCC.
I wanted to see if there is some offical docs on this from HP.
Going through aCC's programmers guide
(https://support.hpe.com/hpesc/public/docDisplay?docLocale=en_US&docId=emr_na-c05054285)
for my version of aCC ("HP C/aC++ B3910B A.06.29 [Oct 18 2016]", "as: HP
Itanium Assembler B.11.31 (HP-UX/itanium)", "ld: 92453-07 linker ld HP
Itanium(R) B.12.65 IPF/IPF"). I cannot find anything relevant to 'weak' in
section 3, or generally in that reference guide.
"Intel(R) Itanium(R) Architecture Assembly Language Reference Guide"
(https://software.intel.com/sites/default/files/m/d/4/1/d/8/asm_lan.pdf) does
mention weak symbols. This is also the same syntax that HP's as seems to
accept.
However in "HP-UX Linker and Libraries User Guide"
(https://support.hpe.com/hpesc/public/docDisplay?docLocale=en_US&docId=a00055697en_us)
on page 59, for nm, it states:
------------------------------
Distinguish between weak and global symbols by appending * to the key letterof
weak symbols.
------------------------------
So it looks like HP's as and ld should support weak symbols so I have decided
to test it.
------------------------------
// main.cc
extern "C" {
void hello() __attribute__ ((weak));
}
int main() {
hello();
return 0;
}
------------------------------
------------------------------
// hello.s
// Adapted from "Hello World" Function Without
// Unwind Directives from Intel Itanium Architecture
// Assembly Language Reference Guide.
.section .rdata, "a", "progbits"
.align 8
.STRING1:
stringz "Hello World!!!\n"
.text
.global hello
.proc hello
hello: alloc loc2 = ar.pfs, 0, 4, 1, 0
mov loc3 = sp
mov loc1 = b0
addl out0 = @ltoff(.STRING1), gp
;;
ld8 out0 = [out0]
mov loc0 = gp
br.call.sptk.many b0 = printf
;;
mov gp = loc0
mov ar.pfs = loc2
mov b0 = loc1
mov sp = loc3
br.ret.sptk.many b0
.endp hello
.weak printf
.type printf, @function
------------------------------
------------------------------
$ aCC +w -g0 +O0 +d -c -o main.o main.cc
$ aCC +w -g0 +O0 +d -S -o main.s main.cc
$ as -o hello.o hello.s
$ aCC +w -g0 +O0 +d -o hello main.o hello.o
------------------------------
Now if I dump hello.o I get printf as a weak symbol as expected:
------------------------------
$ readelf -s -r hello.o
Relocation section '.rela.text' at offset 0xa0 contains 2 entries:
Offset Info Type Sym.Value Sym. Name + Addend
00000010 00000232 R_IA64_LTOFF22 00000000 .rdata + 0
00000020 00000449 R_IA64_PCREL21B 00000000 printf + 0
Symbol table '.symtab' contains 5 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 00000000 0 FILE LOCAL DEFAULT ABS hello.s
2: 00000000 0 SECTION LOCAL DEFAULT 1 .rdata
3: 00000000 80 FUNC GLOBAL DEFAULT 2 hello
4: 00000000 0 FUNC WEAK DEFAULT UND printf
------------------------------
Now the same for main.o, but that that shows that 'hello' is a global symbol
instead of weak as expected.
------------------------------
$ readelf -s -r main.o
Relocation section '.rela.IA_64.unwind' at offset 0x40 contains 3 entries:
Offset Info Type Sym.Value Sym. Name + Addend
00000000 0000045c R_IA64_SEGREL32MS 00000000 .text + 0
00000004 0000045c R_IA64_SEGREL32MS 00000000 .text + 70
00000008 0000095c R_IA64_SEGREL32MS 00000000 .IA_64.unwind_info + 4
Relocation section '.rela.IA_64.unwind_info' at offset 0x7c contains 1 entry:
Offset Info Type Sym.Value Sym. Name + Addend
00000000 00000a5c R_IA64_SEGREL32MS 00000000 .HP.opt_annot + 0
Relocation section '.rela.text' at offset 0x100 contains 1 entry:
Offset Info Type Sym.Value Sym. Name + Addend
00000022 00000b49 R_IA64_PCREL21B 00000000 hello + 0
Relocation section '.rela.debug_info' at offset 0x538 contains 6 entries:
Offset Info Type Sym.Value Sym. Name + Addend
00000006 00000564 R_IA64_SECREL32MS 00000000 .debug_abbrev + 0
0000000c 00000264 R_IA64_SECREL32MS 00000000 .debug_line + 0
00000010 00000364 R_IA64_SECREL32MS 00000000 .debug_actual + 0
00000014 00000764 R_IA64_SECREL32MS 00000000 .debug_macinfo + 0
0000038d 00000424 R_IA64_DIR32MSB 00000000 .text + 0
00000391 00000424 R_IA64_DIR32MSB 00000000 .text + 70
Relocation section '.rela.debug_procs_info' at offset 0x5d4 contains 5 entries:
Offset Info Type Sym.Value Sym. Name + Addend
00000006 00000864 R_IA64_SECREL32MS 00000000 .debug_procs_abbrev + 0
0000000c 00000264 R_IA64_SECREL32MS 00000000 .debug_line + 0
00000010 00000364 R_IA64_SECREL32MS 00000000 .debug_actual + 0
00000049 00000424 R_IA64_DIR32MSB 00000000 .text + 0
0000004d 00000424 R_IA64_DIR32MSB 00000000 .text + 70
Relocation section '.rela.debug_line' at offset 0x680 contains 1 entry:
Offset Info Type Sym.Value Sym. Name + Addend
0000002b 00000424 R_IA64_DIR32MSB 00000000 .text + 0
Relocation section '.rela.debug_actual' at offset 0x6c0 contains 1 entry:
Offset Info Type Sym.Value Sym. Name + Addend
0000001b 00000424 R_IA64_DIR32MSB 00000000 .text + 0
Symbol table '.symtab' contains 13 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 00000000 0 FILE LOCAL DEFAULT ABS main.cc
2: 00000000 0 SECTION LOCAL DEFAULT 14 .debug_line
3: 00000000 0 SECTION LOCAL DEFAULT 16 .debug_actual
4: 00000000 0 SECTION LOCAL DEFAULT 5 .text
5: 00000000 0 SECTION LOCAL DEFAULT 8 .debug_abbrev
6: 00000000 0 SECTION LOCAL DEFAULT 18 .objdebug_file
7: 00000000 0 SECTION LOCAL DEFAULT 19 .debug_macinfo
8: 00000000 0 SECTION LOCAL DEFAULT 13 .debug_procs_abbrev
9: 00000000 0 SECTION LOCAL DEFAULT 3 .IA_64.unwind_info
10: 00000000 0 SECTION LOCAL DEFAULT 7 .HP.opt_annot
11: 00000000 0 FUNC GLOBAL DEFAULT UND hello
12: 00000000 112 FUNC GLOBAL DEFAULT 5 main
------------------------------
Looking at main.s there is:
------------------------------
...
.type hello,@function
.global hello
...
br.call.dptk.many rp = hello#
------------------------------
So it looks like even though aCC accepted weak attribute it generated a global
symbol.
Now some interesting dumps from final executable linked by HP's ld:
------------------------------
$ readelf -s hello
Symbol table '.dynsym' contains 32 entries:
Num: Value Size Type Bind Vis Ndx Name
...
10: 10252e40 0 FUNC WEAK DEFAULT UND printf
25: 04000970 80 FUNC GLOBAL DEFAULT 15 hello
...
45: 10252e40 0 FUNC WEAK DEFAULT UND printf
60: 04000970 80 FUNC GLOBAL DEFAULT 15 hello
...
$ objdump --disassemble=main hello
...
Disassembly of section .text:
040008e0 <main>:
40008e0: 03 08 0d 06 80 05 [MII] alloc r33=ar.pfs,3,3,0
40008e6: 00 00 00 02 00 00 nop.i 0x0;;
40008ec: 04 08 00 84 mov r32=r1;;
40008f0: 01 00 00 00 01 00 [MII] nop.m 0x0
40008f6: 20 02 00 62 00 00 mov r34=b0
40008fc: 00 00 04 00 nop.i 0x0;;
4000900: 19 00 00 00 01 00 [MMB] nop.m 0x0
4000906: 00 00 00 02 00 00 nop.m 0x0
400090c: 78 00 00 52 br.call.dptk.many
b0=4000970 <hello>;;
4000910: 03 08 00 40 00 21 [MII] mov r1=r32
4000916: 00 00 00 02 00 20 nop.i 0x0;;
400091c: 01 00 00 90 mov r9=0;;
4000920: 03 40 00 12 00 21 [MII] mov r8=r9
4000926: 00 00 00 02 00 00 nop.i 0x0;;
400092c: 20 0a 00 07 mov b0=r34;;
4000930: 02 00 00 00 01 00 [MII] nop.m 0x0
4000936: 00 08 01 55 00 00 mov.i ar.pfs=r33;;
400093c: 00 00 04 00 nop.i 0x0
4000940: 19 00 00 00 01 00 [MMB] nop.m 0x0
4000946: 00 00 00 02 00 80 nop.m 0x0
400094c: 08 00 84 02 br.ret.dptk.many b0;;
$ objdump --disassemble=hello hello
...
Disassembly of section .text:
04000970 <hello>:
4000970: 08 10 15 08 80 05 [MMI] alloc r34=ar.pfs,5,4,0
4000976: 30 02 30 00 42 20 mov r35=r12
400097c: 04 00 c4 00 mov r33=b0
4000980: 0a 20 e1 fb ff 27 [MMI] addl r36=-8,r1;;
4000986: 40 02 90 30 20 00 ld8 r36=[r36]
400098c: 04 08 00 84 mov r32=r1
4000990: 17 00 f2 ff 3f 16 [BBB] br.call.sptk.many
b0=4000950 <.stub>
4000996: 00 00 00 00 10 00 nop.b 0x0
400099c: 00 00 00 20 nop.b 0x0;;
40009a0: 00 08 00 40 00 21 [MII] mov r1=r32
40009a6: 00 10 01 55 00 00 mov.i ar.pfs=r34
40009ac: 10 0a 00 07 mov b0=r33
40009b0: 12 60 00 46 00 21 [MBB] mov r12=r35
40009b6: 40 04 00 42 00 00 br.ret.sptk.many b0
40009bc: 00 00 00 20 nop.b 0x0
$ objdump --disassemble=.stub hello
...
Disassembly of section .text:
04000950 <.stub>:
4000950: 0b 78 a0 fb ff 27 [MMI] addl r15=-24,r1;;
4000956: 00 41 3c 30 28 c0 ld8 r16=[r15],8
400095c: 01 08 00 84 mov r14=r1;;
4000960: 11 08 00 1e 18 10 [MIB] ld8 r1=[r15]
4000966: 60 80 04 80 03 00 mov b6=r16
400096c: 60 00 80 00 br.few b6;;
$ readelf -r hello
Relocation section '.rela.plt' at offset 0x7e4 contains 1 entry:
Offset Info Type Sym.Value Sym. Name + Addend
40010000 00000a80 R_IA64_IPLTMSB 10252e40 printf + 0
------------------------------
And that R_IA64_IPLTMSB relocation seems to be expected since printf is in
shared lib. So I guess we need to figure out how to force aCC to actually
respect __attribute__((weak)).
What do you think?
Thanks!
--peter
