.cfi_sections directives should go before CFI generation start

[llvmbot]

Bugzilla Link	29017
Version	trunk
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@compnerd,@echristo,@ismail,@kraj

Extended Description

Currently, the DwarfCFIException class writes the sections that the CFI emits (via a .cfi_sections directive) within its endModule() method, after all the other CFI info has already been output. This renders the resulting .s files impossible for gnu as to process, since by the rules gnu as uses for the .cfi* directives the last .cfi_sections directive must precede the first .cfi_startproc directive (see 7.10.1 @ https://sourceware.org/binutils/docs/as/CFI-directives.html). This rule has been enforced in gas since Feb 2016 (commit bd5608dcc6a76876db06b1af1852252a4282aa2f), after the 2.26 release, and I've been able to reproduce it for aarch64 and sparc, like this:

cd binutils-build
../binutils-x86/configure --target=aarch64-linux && make
cd ../t
cat t.c
int main()
{
}
../clang-build/bin/clang 1.c -S -O0 -ggdb -target aarch64
../binutils-build/gas/as-new 1.s
t.s: Assembler messages:
t.s:142: Error: inconsistent uses of .cfi_sections

This problem has also been reported at http://lists.llvm.org/pipermail/llvm-dev/2016-August/103519.html.

[echristo]

Yay. :\

commit bd5608dcc6a76876db06b1af1852252a4282aa2f
Author: Nick Clifton nickc@redhat.com
Date: Thu Feb 11 15:30:55 2016 +0000

Allow the .cfi_sections directive to be reissued provided that CFI generation has not yet started.

	PR gas/19614
	* dw2gencfi.c (cfi_sections_set): Delay setting this variable
	until it is actually used.
	(cfi_set_sections): Set cfi_sections_set to true.
	(dot_cfi_startproc): Likewise.
	(dot_cfi_endproc): Likewise.
	(dot_cfi_fde_data): Likewise.
	(cfi_finish): Likewise.
	(dot_cfi_sections): Do not set cfi_sections_set.
	* doc/as.texinfo (.cfi_sections): Note that targets can provide
	their own cfi section name.  Also note that the directive can be
	reissued provided that CFI generation has not started.
	* testsuite/gas/mips/compact-eh-err2.s: Add .cfi_startproc and
	.cfi_endproc directives so that the redefinition of .cfi_sections
	will trigger the generation of the error message.
	* testsuite/gas/mips/compact-eh-err2.l: Update expected line
	number of error message.

[kraj]

I also needed to backport

https://sourceware.org/bugzilla/show_bug.cgi?id=20648

otherwise gas failed with same error with clang/trunk on armv7