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Date: Mon, 18 May 2015 15:34:40 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] Build process uses script to add CFI directives
 to x86 asm

* Alex Dowad <alexinbeijing@...il.com> [2015-05-16 15:54:31 +0200]:
> 
> configure script now checks whether debugging is enabled, whether the assembler
> understands CFI directives, whether it understands '-x assembler', and whether
> there the AWK script is present for the current arch.
> 
> aswrap.sh is gone -- the problem is that the arguments it wants (and the order it
>   wants them in) is different from $(CC). So it's hard to use an AS_CMD variable
>   as suggested by RF to run whichever command is appropriate.
> 
> Suggestions from shell/Makefile scripting wizards on how to do this better
>   are appreciated!
> 

it is possible to parse the options but not trivial

may be have the arguments in an order that's good for the wrapper

> The processed asm now contains .file and .loc directives, so when you debug it in
> GDB, it will show you the original source file, and highlight the correct lines.
> 

nice

> I haven't tested with busybox awk yet, just with GNU awk. If there are no further
>   issues with the code, I will do that next.
> 

i see one issue: \s, \w may not be supported (eg mawk does not have them
nor [[:space:]] char classes)

> 
>  Makefile               |  10 ++-
>  configure              |  13 ++++
>  tools/add-cfi.awk.i386 | 207 +++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 229 insertions(+), 1 deletion(-)
>  create mode 100644 tools/add-cfi.awk.i386
> 
> diff --git a/Makefile b/Makefile
> index 6559295..6f17cc7 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: $(ARCH)/%.s
> +ifeq ($(ADD_CFI),yes)
> +	LC_ALL=C awk -f tools/add-cfi.awk.$(ARCH) $< | $(CC) $(CFLAGS_ALL_STATIC) -x assembler -c -o $@ -
> +else
>  	$(CC) $(CFLAGS_ALL_STATIC) -c -o $@ $<
> +endif
>  

this may work, with a reasonably simple aswrap script:

%.o: $(ARCH)/%.s
	$(ASWRAP) $(ARCH) $< $(CC) $(CFLAGS_ALL_STATIC) -c -o $@

i don't know which approach is less ugly.

the %.sub rules should be handled too..

> diff --git a/configure b/configure
> index 143dc92..72349a2 100755
> --- a/configure
> +++ b/configure
> @@ -317,6 +317,18 @@ tryflag CFLAGS_MEMOPS -fno-tree-loop-distribute-patterns
>  test "$debug" = yes && CFLAGS_AUTO=-g
>  
>  #
> +# Preprocess asm files to add extra debugging information if debug is
> +# enabled, our assembler supports the needed directives, and the
> +# preprocessing script has been written for our architecture.
> +#
> +if (test "$debug" = yes) &&
> +   (test -f "tools/add-cfi.awk.$ARCH") &&
> +   (echo ".cfi_startproc\n.cfi_endproc" | $CC -x assembler -c -o /dev/null -)
> +then
> +  ADD_CFI=yes
> +fi
> +

else ADD_CFI=no

(otherwise an ADD_CFI env var may influence configure behaviour)

> +#
>  # Possibly add a -O option to CFLAGS and select modules to optimize with
>  # -O3 based on the status of --enable-optimize and provided CFLAGS.
>  #
> @@ -570,6 +582,7 @@ LDFLAGS = $LDFLAGS_AUTO $LDFLAGS
>  CROSS_COMPILE = $CROSS_COMPILE
>  LIBCC = $LIBCC
>  OPTIMIZE_GLOBS = $OPTIMIZE_GLOBS
> +ADD_CFI = $ADD_CFI
>  EOF
>  test "x$static" = xno && echo "STATIC_LIBS ="
>  test "x$shared" = xno && echo "SHARED_LIBS ="

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