PR28149, debug info with wrong file association

[Alan Modra]

On Fri, Sep 17, 2021 at 09:25:33AM +0200, Eric Botcazou wrote:
> > gcc-11 and gcc-12 pass -gdwarf-5 to gas, in order to prime gas for
> > DWARF 5 level debug info.  Unfortunately it seems there are cases
> > where the compiler does not emit a .file or .loc dwarf debug directive
> > before any machine instructions.  (Note that the .file directive
> > typically emitted as the first line of assembly output doesn't count as
> > a dwarf debug directive.  The dwarf .file has a file number before the
> > file name string.)
> 
> That"s no longer true in DWARF 5, as there is always a .file 0 directive now.

I did check before making that statement.  :-)

A freshly built x86_64-linux mainline gcc compiling this testcase

asm("nop");
int main () 
{
  return 0;
}

~/build/gcc/gcc/xgcc -B ~/build/gcc/gcc/ -g pr28149.c -v -save-temps
shows the assembler being invoked with --gdwarf-5 on the following

	.file	"pr28149.c"
	.text
.Ltext0:
#APP
	nop
#NO_APP
	.globl	main
	.type	main, @function
main:
.LFB0:
	.file 1 "pr28149.c"
	.loc 1 3 1
	.cfi_startproc
[snip rest]

So we have an instruction being emitted before gas generated line info
is turned off at ".file 1 ...".

-- 
Alan Modra
Australia Development Lab, IBM