[PATCH] Enable unwind info in libc-start.c and backtrace.c

[Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>]

After feedback on https://sourceware.org/ml/libc-alpha/2017-07/msg01010.html
here is the updated patch:

Add unwind info to __libc_start_main so that unwinding continues one
extra level to _start.  Similarly add unwind info to backtrace.
Given many targets require this, do this in a general way and remove
-funwind-tables (or -fexceptions - which is identical in C) from several
target makefiles.

ChangeLog:
2017-08-09  Wilco Dijkstra  <wdijkstr@arm.com>

        * sysdeps/aarch64/Makefile: Build libc-start.c with -fexceptions.
        * csu/Makefile: Add -funwind-tables to libc-start.c.
        * debug/Makefile: Add -funwind-tables to backtrace.c.
        * sysdeps/aarch64/Makefile: Remove CFLAGS-backtrace.c.
        * sysdeps/arm/Makefile: Likewise.
        * sysdeps/i386/Makefile: Likewise.
        * sysdeps/m68k/Makefile: Likewise.
        * sysdeps/mips/Makefile: Likewise.
        * sysdeps/nios2/Makefile: Likewise.
        * sysdeps/sh/Makefile: Likewise.
        * sysdeps/sparc/Makefile: Likewise.
--
 

diff --git a/csu/Makefile b/csu/Makefile
index 88646b6e8f068c09c5743fd908b08d15064294ee..490d0b0f3b63318381e59fc35038801f682d20a2 100644
--- a/csu/Makefile
+++ b/csu/Makefile
@@ -82,6 +82,9 @@ extra-objs += $(crtstuff:=.o)
 extra-objs += abi-note.o init.o
 asm-CPPFLAGS += -I$(objpfx).
 
+# Enable unwinding so backtrace unwinds to __libc_start_main
+CFLAGS-libc-start.c += -funwind-tables
+
 include ../Rules
 
 # Make these in the lib pass so they're available in time to link things with.
diff --git a/debug/Makefile b/debug/Makefile
index cd4975c35b70fe4c52fc6bbedb0f88179463af9c..620a0b71f5919d41cc5cb41d0943193d8e7b6ac5 100644
--- a/debug/Makefile
+++ b/debug/Makefile
@@ -59,7 +59,7 @@ static-only-routines := warning-nop stack_chk_fail_local
 CFLAGS-stack_chk_fail.c = $(no-stack-protector)
 CFLAGS-stack_chk_fail_local.c = $(no-stack-protector)
 
-CFLAGS-backtrace.c = -fno-omit-frame-pointer
+CFLAGS-backtrace.c = -fno-omit-frame-pointer -funwind-tables
 CFLAGS-sprintf_chk.c = $(libio-mtsafe)
 CFLAGS-snprintf_chk.c = $(libio-mtsafe)
 CFLAGS-vsprintf_chk.c = $(libio-mtsafe)
diff --git a/sysdeps/aarch64/Makefile b/sysdeps/aarch64/Makefile
index 562c1373aebee6ffb4ff5c2071a23d007a8e07ba..5f3e20371accfb001de6dff342bb323b424324ca 100644
--- a/sysdeps/aarch64/Makefile
+++ b/sysdeps/aarch64/Makefile
@@ -1,9 +1,5 @@
 long-double-fcts = yes
 
-ifeq ($(subdir),debug)
-CFLAGS-backtrace.c += -funwind-tables
-endif
-
 ifeq ($(subdir),elf)
 sysdep-dl-routines += tlsdesc dl-tlsdesc
 gen-as-const-headers += dl-link.sym
diff --git a/sysdeps/arm/Makefile b/sysdeps/arm/Makefile
index 2849aeda4238997975c5a8096da474e54da26932..ad2042b93a156867f586bedaaba4b120a93f676c 100644
--- a/sysdeps/arm/Makefile
+++ b/sysdeps/arm/Makefile
@@ -51,11 +51,6 @@ sysdep_routines += $(aeabi_constants) $(aeabi_routines)
 static-only-routines += $(aeabi_constants) aeabi_read_tp
 shared-only-routines += libc-aeabi_read_tp
 
-# In order for unwinding to fail when it falls out of main, we need a
-# cantunwind marker.  There's one in start.S.  To make sure we reach it, add
-# unwind tables for __libc_start_main.
-CFLAGS-libc-start.c += -fexceptions
-
 sysdep_routines += arm-unwind-resume
 shared-only-routines += arm-unwind-resume
 endif
@@ -64,10 +59,6 @@ ifeq ($(subdir),gmon)
 sysdep_routines += arm-mcount
 endif
 
-ifeq ($(subdir),debug)
-CFLAGS-backtrace.c += -funwind-tables
-endif
-
 ifeq ($(subdir),rt)
 librt-sysdep_routines += rt-aeabi_unwind_cpp_pr1 rt-arm-unwind-resume
 librt-shared-only-routines += rt-aeabi_unwind_cpp_pr1 rt-arm-unwind-resume
diff --git a/sysdeps/i386/Makefile b/sysdeps/i386/Makefile
index e30e1339f0554dd53be1ab881cb4df04de820792..a1500454e5a977415b8bd120326f3db104d18df2 100644
--- a/sysdeps/i386/Makefile
+++ b/sysdeps/i386/Makefile
@@ -19,10 +19,6 @@ CFLAGS-dl-load.c += -Wno-unused
 CFLAGS-dl-reloc.c += -Wno-unused
 endif
 
-ifeq ($(subdir),debug)
-CFLAGS-backtrace.c += -fexceptions
-endif
-
 # Most of the glibc routines don't ever call user defined callbacks
 # nor use any FPU or SSE* and as such don't need bigger %esp alignment
 # than 4 bytes.
diff --git a/sysdeps/m68k/Makefile b/sysdeps/m68k/Makefile
index 26539fa01d38a5ba1260cb1fda153470513d2e29..b6910014f8fe75591026381d4b6a9e02301740d7 100644
--- a/sysdeps/m68k/Makefile
+++ b/sysdeps/m68k/Makefile
@@ -40,10 +40,6 @@ ifeq ($(subdir),setjmp)
 CFLAGS-setjmp.c := -fno-omit-frame-pointer
 endif
 
-ifeq ($(subdir),debug)
-CFLAGS-backtrace.c += -funwind-tables
-endif
-
 ifeq ($(subdir),elf)
 CFLAGS-rtld.c += -Wno-uninitialized -Wno-unused
 endif
diff --git a/sysdeps/mips/Makefile b/sysdeps/mips/Makefile
index 7c1d77941ec154b460af9b2581cec7e82141acdf..fd891ddf09855adaac3d50f57ca9bd245fbc16e2 100644
--- a/sysdeps/mips/Makefile
+++ b/sysdeps/mips/Makefile
@@ -12,10 +12,6 @@ librt-sysdep_routines += rt-sysdep
 librt-shared-only-routines += rt-sysdep
 endif
 
-ifeq ($(subdir),debug)
-CFLAGS-backtrace.c += -funwind-tables
-endif
-
 ifeq ($(subdir),csu)
 CPPFLAGS-crti.S += $(pic-ccflag)
 CPPFLAGS-crtn.S += $(pic-ccflag)
diff --git a/sysdeps/nios2/Makefile b/sysdeps/nios2/Makefile
index 75cab5e5b8fc04e916ced8e1b9c3a8ecc657b85d..9ceab11297a7d215e3a30d3ecf2210029a89a51b 100644
--- a/sysdeps/nios2/Makefile
+++ b/sysdeps/nios2/Makefile
@@ -29,7 +29,3 @@ endif
 ifeq ($(subdir),csu)
 gen-as-const-headers += tcb-offsets.sym
 endif
-
-ifeq ($(subdir),debug)
-CFLAGS-backtrace.c += -funwind-tables
-endif
diff --git a/sysdeps/sh/Makefile b/sysdeps/sh/Makefile
index 0c6db9a9d41d56defb946fcc31e0767c7a853611..de8fa0bc0e81e8b7e1ef946b7106408cf4ac7cd1 100644
--- a/sysdeps/sh/Makefile
+++ b/sysdeps/sh/Makefile
@@ -5,7 +5,3 @@ endif
 ifeq ($(subdir),gmon)
 sysdep_routines += _mcount
 endif
-
-ifeq ($(subdir),debug)
-CFLAGS-backtrace.c += -funwind-tables
-endif
diff --git a/sysdeps/sparc/Makefile b/sysdeps/sparc/Makefile
index 31aaeaed8f8e601b578908e13a6f99352346f753..3f0c0964002560f03817905f390821aef176d52c 100644
--- a/sysdeps/sparc/Makefile
+++ b/sysdeps/sparc/Makefile
@@ -3,10 +3,6 @@ long-double-fcts = yes
 
 pie-ccflag = -fPIE
 
-ifeq ($(subdir),debug)
-CFLAGS-backtrace.c += -funwind-tables
-endif
-
 ifeq ($(subdir),gmon)
 sysdep_routines += sparc-mcount
 endif