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Date: Tue, 12 May 2015 18:52:13 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] First prototype of script which adds CFI
 directives to x86 asm

On Tue, May 12, 2015 at 11:28:44PM +0200, Alex Dowad wrote:
> Some functions implemented in asm need to use EBP for purposes other than acting
> as a frame pointer. (Notably, it is used for the 6th argument to syscalls with
> 6 arguments.) Without frame pointers, GDB can only show backtraces if it gets
> CFI information from a .debug_frame or .eh_frame ELF section.

Thanks! Some quick initial review, without testing/reviewing script
contents in detail:

>  Makefile               |   4 ++
>  tools/add-cfi.awk.i386 | 152 +++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 156 insertions(+)
>  create mode 100644 tools/add-cfi.awk.i386
> 
> diff --git a/Makefile b/Makefile
> index 6559295..f7335aa 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -118,7 +118,11 @@ $(foreach s,$(wildcard src/*/$(ARCH)*/*.s),$(eval $(call mkasmdep,$(s))))
>  	$(CC) $(CFLAGS_ALL_STATIC) -c -o $@ $(dir $<)$(shell cat $<)
>  
>  %.o: $(ARCH)/%.s
> +ifeq ($(ARCH),i386)
> +	awk -f tools/add-cfi.awk.i386 $< | $(CC) $(CFLAGS_ALL_STATIC) -x assembler -c -o $@ -
> +else
>  	$(CC) $(CFLAGS_ALL_STATIC) -c -o $@ $<
> +endif

Here I'd like to see the arch passed to the script, and the script
acting as a nop for archs it doesn't support, rather than a
conditional in the makefile.

Also if we're using -x assembler and input from stdin, configure will
need to check for these and fall back to no cfi generation if they
don't work.

Possibly these could be combined by using a tools/aswrap.sh with the
piping (or temp file, which wouldn't need special compiler-driver
support) logic in it and the logic for calling a different awk script
per arch or none at all, if you prefer to keep them as separate awk
scripts.

Rich

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