Re: [PATCH 1/2] x86: improve .debug_line contents for assembly sources

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Apr 14, 2022 at 03:31:26PM +0200, Roger Pau Monné wrote:
> On Thu, Apr 14, 2022 at 02:52:47PM +0200, Jan Beulich wrote:
> > On 14.04.2022 14:40, Roger Pau Monné wrote:
> > > On Tue, Apr 12, 2022 at 12:27:34PM +0200, Jan Beulich wrote:
> > >> While future gas versions will allow line number information to be
> > >> generated for all instances of .irp and alike [1][2], the same isn't
> > >> true (nor immediately intended) for .macro [3]. Hence macros, when they
> > >> do more than just invoke another macro or issue an individual insn, want
> > >> to have .line directives (in header files also .file ones) in place.
> > >>
> > >> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> > >>
> > >> [1] 
> > >> https://sourceware.org/git?p=binutils-gdb.git;a=commitdiff;h=7992631e8c0b0e711fbaba991348ef6f6e583725
> > >> [2] 
> > >> https://sourceware.org/git?p=binutils-gdb.git;a=commitdiff;h=2ee1792bec225ea19c71095cee5a3a9ae6df7c59
> > >> [3] 
> > >> https://sourceware.org/git?p=binutils-gdb.git;a=commitdiff;h=6d1ace6861e999361b30d1bc27459ab8094e0d4a
> > >> ---
> > >> Using .file has the perhaps undesirable side effect of generating a fair
> > >> amount of (all identical) STT_FILE entries in the symbol table. We also
> > >> can't use the supposedly assembler-internal (and hence undocumented)
> > >> .appfile anymore, as it was removed [4]. Note that .linefile (also
> > >> internal/undocumented) as well as the "# <line> <file>" constructs the
> > >> compiler emits, leading to .linefile insertion by the assembler, aren't
> > >> of use anyway as these are processed and purged when processing .macro
> > >> [3].
> > >>
> > >> [4] 
> > >> https://sourceware.org/git?p=binutils-gdb.git;a=commitdiff;h=c39e89c3aaa3a6790f85e80f2da5022bc4bce38b
> > >>
> > >> --- a/xen/arch/x86/include/asm/spec_ctrl_asm.h
> > >> +++ b/xen/arch/x86/include/asm/spec_ctrl_asm.h
> > >> @@ -24,6 +24,8 @@
> > >>  #include <asm/msr-index.h>
> > >>  #include <asm/spec_ctrl.h>
> > >>  
> > >> +#define FILE_AND_LINE .file __FILE__; .line __LINE__
> > > 
> > > Seeing as this seems to get added to all macros below, I guess you did
> > > consider (and discarded) introducing a preprocessor macro do to the
> > > asm macro definitons:
> > > 
> > > #define DECLARE_MACRO(n, ...) \
> > > .macro n __VA_ARGS__ \
> > >     .file __FILE__; .line __LINE__
> > 
> > No, I didn't even consider that. I view such as too obfuscating - there's
> > then e.g. no visual match with the .endm. Furthermore, as outlined in the
> > description, I don't think this wants applying uniformly. There are
> > macros which better don't have this added. Yet I also would prefer to not
> > end up with a mix of .macro and DECLARE_MACRO().
> 
> I think it's a dummy question, but why would we want to add this to
                                              ^n't

Sorry.