http://sourceware.org/ml/gdb-patches/2016-10/msg00652.html

Subject: [testsuite patch] Fix false FAIL for gdb.base/morestack.exp

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Hi,

since

	[commit] [testsuite patch] Fix gcc_compiled for gcc 6 & 7

	https://sourceware.org/ml/gdb-patches/2016-10/msg00620.html

there has started running again

	 Running gdb/testsuite/gdb.base/morestack.exp ...

	+FAIL: gdb.base/morestack.exp: continue

	+PASS: gdb.base/morestack.exp: up 3000

but as you can see it FAILs now - on Fedora 24 x86_64 (although for example it

still PASSes on CentOS-7.2 x86_64).

Program received signal SIGSEGV, Segmentation fault.

0x00007ffff787c7bb in malloc_consolidate (av=av@entry=0x7ffff7bbcb00 <main_arena>) at malloc.c:4181

4181		      unlink(av, nextchunk, bck, fwd);

(gdb) bt

#0  0x00007ffff787c7bb in malloc_consolidate (av=av@entry=0x7ffff7bbcb00 <main_arena>) at malloc.c:4181

#1  0x00007ffff787f235 in _int_malloc (av=av@entry=0x7ffff7bbcb00 <main_arena>, bytes=bytes@entry=1024) at malloc.c:3448

[...]

#8  0x00007ffff784c5ac in _IO_vfprintf_internal (s=0x7ffff7bbd600 <_IO_2_1_stdout_>, format=<optimized out>, ap=ap@entry=0x7ffff77fd7f8) at vfprintf.c:1631

#9  0x00007ffff7853939 in __printf (format=<optimized out>) at printf.c:33

#10 0x0000000000400d6b in down ()

#11 0x0000000000400f2c in __morestack ()

#12 0x0000000000400dda in down ()

[...]

This apparently is due to - man gcc - -fsplit-stack:

	When code compiled with -fsplit-stack calls code compiled without

	-fsplit-stack, there may not be much stack space available for the

	latter code to run.  If compiling all code, including library code,

	with -fsplit-stack is not an option, then the linker can fix up these

	calls so that the code compiled without -fsplit-stack always has

	a large stack.  Support for this is implemented in the gold linker in

	GNU binutils release 2.21 and later.

Personally I do not understand why gold is not the default linker as GNU ld is

unusably slow (6x) for C++ but that is off-topic here.

OK for check-in?

Thanks,

Jan

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gdb/testsuite/ChangeLog

2016-10-22  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.base/morestack.exp: Try to build it using -fuse-ld=gold first.

diff --git a/gdb/testsuite/gdb.base/morestack.exp b/gdb/testsuite/gdb.base/morestack.exp

index 12f5d28..caa85b8 100644

--- a/gdb/testsuite/gdb.base/morestack.exp

+++ b/gdb/testsuite/gdb.base/morestack.exp

@@ -23,7 +23,11 @@ if {$gcc_compiled == 0} {

 standard_testfile

-if { [prepare_for_testing ${testfile}.exp ${testfile} $srcfile {additional_flags=-fsplit-stack}] } {

+# -fuse-ld=gold is used for calling printf code built without -fsplit-stack

+# which could crash otherise.  See GCC documentation of -fsplit-stack.

+set opts "additional_flags=-fsplit-stack"

+if { [prepare_for_testing ${testfile}.exp ${testfile} $srcfile [list $opts additional_flags=-fuse-ld=gold]] \

+     && [prepare_for_testing ${testfile}.exp ${testfile} $srcfile $opts] } {

     return -1

 }

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