What steps reproduce the problem?

hg clone tip
cd $GOROOT/src
./make.bash
cd pkg/net/http
go test -c
gdb ./http.test
break strings.Repeat
run

What happened?

Reading symbols from /home/albert/go/src/pkg/net/http/http.test...done.
Loading Go Runtime support.
(gdb) break strings.Repeat
Breakpoint 1 at 0x535cfb: strings.Repeat. (2 locations)
(gdb) run
Starting program: /home/albert/go/src/pkg/net/http/http.test 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
[New Thread 0x7ffff7e2b700 (LWP 12059)]
runtime: unexpected return pc for flag.(*FlagSet).parseOne called from 0x1a
runtime: unexpected return pc for flag.(*FlagSet).parseOne called from 0x1a
fatal error: unknown caller pc

runtime stack:
runtime.throw(0xa0b471)
    /home/albert/go/src/pkg/runtime/panic.c:520 +0x69 fp=0x7fffffffd8d8
runtime.gentraceback(0x40a962, 0xc2080674a8, 0x0, 0xc208002120, 0xc200000000, 0x0,
0x7fffffff, 0x4090c0, 0x7fffffffdaa0, 0x0)
    /home/albert/go/src/pkg/runtime/traceback_x86.c:167 +0x819 fp=0x7fffffffd9a0
addstackroots(0xc208002120, 0x7fffffffdaa0)
    /home/albert/go/src/pkg/runtime/mgc0.c:1676 +0x168 fp=0x7fffffffda30
markroot(0xc20800c900, 0x2b00000005)
    /home/albert/go/src/pkg/runtime/mgc0.c:1309 +0xbe fp=0x7fffffffdab0
runtime.parfordo(0xc20800c900)
    /home/albert/go/src/pkg/runtime/parfor.c:88 +0xa3 fp=0x7fffffffdb28
gc(0xc2080674c0)
    /home/albert/go/src/pkg/runtime/mgc0.c:2387 +0x1d6 fp=0x7fffffffdc58
mgc(0xc208002120)
    /home/albert/go/src/pkg/runtime/mgc0.c:2329 +0x2e fp=0x7fffffffdc68
runtime.mcall(0x42b587)
    /home/albert/go/src/pkg/runtime/asm_amd64.s:181 +0x4b fp=0x7fffffffdc78

goroutine 16 [garbage collection]:
runtime.gc(0xc200000000)
    /home/albert/go/src/pkg/runtime/mgc0.c:2309 +0x1b2 fp=0xc2080674d0
runtime.mallocgc(0xbdc000, 0x6ff561, 0x1)
    /home/albert/go/src/pkg/runtime/malloc.goc:204 +0x1d6 fp=0xc208067538
cnew(0x6ff560, 0xbdb328, 0x1)
    /home/albert/go/src/pkg/runtime/malloc.goc:835 +0xc1 fp=0xc208067558
runtime.cnewarray(0x6ff560, 0xbdb328)
    /home/albert/go/src/pkg/runtime/malloc.goc:848 +0x3a fp=0xc208067578
makeslice1(0x6ed6c0, 0x0, 0xbdb328, 0xc2080675d8)
    /home/albert/go/src/pkg/runtime/slice.goc:55 +0x4d fp=0xc208067590
runtime.makeslice(0x6ed6c0, 0x0, 0xbdb328, 0x0, 0x0, 0xbdb328)
    /home/albert/go/src/pkg/runtime/slice.goc:36 +0xb3 fp=0xc2080675c0
strconv.quoteWith(0x53605a, 0x7e7770, 0x22, 0x0, 0x0)
    /home/albert/go/src/pkg/strconv/quote.go:15 +0x79 fp=0xc2080676a8
strconv.Quote(0x53605a, 0x7e7770, 0x0, 0x0)
    /home/albert/go/src/pkg/strconv/quote.go:91 +0x4d fp=0xc2080676d8
fmt.(*fmt).fmt_q(0xc208026060, 0x53605a, 0x7e7770)
    /home/albert/go/src/pkg/fmt/format.go:334 +0x11f fp=0xc208067728
fmt.(*pp).fmtString(0xc208026000, 0x53605a, 0x7e7770, 0x71)
    /home/albert/go/src/pkg/fmt/print.go:517 +0xa2 fp=0xc208067758
fmt.(*pp).printArg(0xc208026000, 0x6ff160, 0xc208000f20, 0x71, 0x0, 0x0)
    /home/albert/go/src/pkg/fmt/print.go:780 +0xabb fp=0xc2080677d8
fmt.(*pp).doPrintf(0xc208026000, 0x85b1f0, 0x24, 0xc208067dd0, 0x3, 0x3)
    /home/albert/go/src/pkg/fmt/print.go:1159 +0x2044 fp=0xc208067b20
fmt.Sprintf(0x85b1f0, 0x24, 0xc208067dd0, 0x3, 0x3, 0x0, 0x0)
    /home/albert/go/src/pkg/fmt/print.go:203 +0x7c fp=0xc208067b70
fmt.Errorf(0x85b1f0, 0x24, 0xc208067dd0, 0x3, 0x3, 0x0, 0x0)
    /home/albert/go/src/pkg/fmt/print.go:212 +0x6c fp=0xc208067bc8
flag.(*FlagSet).failf(0x5432d1, 0x85b1f0, 0x24, 0xc208067dd0, 0x3, 0x3, 0x0, 0x0)
    /home/albert/go/src/pkg/flag/flag.go:694 +0x83 fp=0xc208067c68
runtime: unexpected return pc for flag.(*FlagSet).parseOne called from 0x1a
flag.(*FlagSet).parseOne(0x5432d1, 0xc20802c120, 0xc208000010, 0x0)
    /home/albert/go/src/pkg/flag/flag.go:758 +0x76a fp=0xc208067e08
created by _rt0_go
    /home/albert/go/src/pkg/runtime/asm_amd64.s:97 +0x120

goroutine 17 [runnable]:
runtime.MHeap_Scavenger()
    /home/albert/go/src/pkg/runtime/mheap.c:507 fp=0x7ffff7febfa8
runtime.goexit()
    /home/albert/go/src/pkg/runtime/proc.c:1430 fp=0x7ffff7febfb0
created by runtime.main
    /home/albert/go/src/pkg/runtime/proc.c:207

goroutine 18 [runnable]:
bgsweep()
    /home/albert/go/src/pkg/runtime/mgc0.c:1960 fp=0x7ffff7fdcfa8
runtime.goexit()
    /home/albert/go/src/pkg/runtime/proc.c:1430 fp=0x7ffff7fdcfb0
created by runtime.gc
    /home/albert/go/src/pkg/runtime/mgc0.c:2249

goroutine 19 [runnable]:
runfinq()
    /home/albert/go/src/pkg/runtime/mgc0.c:2586 fp=0x7ffff7feafa8
runtime.goexit()
    /home/albert/go/src/pkg/runtime/proc.c:1430 fp=0x7ffff7feafb0
created by runtime.gc
    /home/albert/go/src/pkg/runtime/mgc0.c:2249
[Thread 0x7ffff7e2b700 (LWP 12059) exited]
[Inferior 1 (process 12055) exited with code 02]


Please provide any additional information below.

Fedora Core 20 x86_64 with most updates installed

gdb-7.6.50.20130731-19.fc20.x86_64