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Message-ID: <20150514025720.GB17573@brightrain.aerifal.cx> Date: Wed, 13 May 2015 22:57:20 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: [PATCH v3] Build process uses script to add CFI directives to x86 asm On Wed, May 13, 2015 at 09:22:52PM +0200, Szabolcs Nagy wrote: > * Alex Dowad <alexinbeijing@...il.com> [2015-05-13 19:54:39 +0200]: > > > > I've noticed that using tempfiles for the augmented asm has a drawback: > > In the source file/line debugging info generated by the assembler, it records > > the source file as "/tmp/<random-garbage>". Then, when you try to debug a program > > which is linked against the resulting musl, GDB tries to open "/tmp/<random-garbage>" > > to show in the source window. > > > > Suggestions?? Perhaps generate .cfi.s files as Szabolcs suggested?? > > > > you can use > > .file "foo.s" One question -- will the fact that the line numbers don't match up interfere with debugging? If so, the CFI generation should add the directives to existing lines separated by ;'s rather than inserting lines. > > diff --git a/Makefile b/Makefile > > index 6559295..9aefd62 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -118,7 +118,7 @@ $(foreach s,$(wildcard src/*/$(ARCH)*/*.s),$(eval $(call mkasmdep,$(s)))) > > $(CC) $(CFLAGS_ALL_STATIC) -c -o $@ $(dir $<)$(shell cat $<) > > > > %.o: $(ARCH)/%.s > > - $(CC) $(CFLAGS_ALL_STATIC) -c -o $@ $< > > + tools/aswrap.sh $< $@ $(ARCH) "$(CC) $(CFLAGS_ALL_STATIC)" > > > > i think passing down the build command that way is not ok The quoting is probably off, but otherwise it doesn't look so bad. > " may be used inside CFLAGS (and there are other shell quote issues) > it hides the build command in the make output > it's not clear if the build correctly handles if CC fails Do you have a better design in mind? > > +function get_const1() { > > + # for instructions with 2 operands, get 1st operand (assuming it is constant) > > + match($0, /-?(0x[0-9a-fA-F]+|[0-9]+),/) > > + return parse_const(substr($0, RSTART, RLENGTH-1)) > > +} > > it only matches with immediate , > > i'd just clean the whitespaces up so you dont have to add \s* or \s+ > to every regex (see below) > > awk converts strings to numbers, but hex is unfortunately not guaranteed > to be supported (otherwise strtod conversion rules apply) > > but you can implement parse_const(s) as > > sign = sub(/^-/,"",s) > hex = sub(/^0x/,"",s) > if (hex) > n = hex2int(s) > else > n = s+0 > return sign ? -n : n > > this does not handle binary (0b11) and octal (0123) asm consts > (i think you should check for those and emit a warning). Is 0b something that could even be relied upon? We generally use a minimal asm dialect without extensions that real or hypothetical alternate assemblers might not have. I'm happy with a YAGNI approach to the CFI generation. > > +/^.global\s+\w+/ { > > + globals[$2] = 1 > > may be spelt as .globl too Yes, that might be used somewhere. > > +/pushl?/ { > > + if (match($0, /\s+%(ax|bx|cx|dx|di|si|bp|sp)/)) > > + adjust_sp_offset(2) > > + else > > + adjust_sp_offset(4) > > +} > > i think > > pushl $123 > push $123 > > are different How so? Likewise I don't think the stuff for 2-byte push/pop is terribly useful. It's not a meaningful operation to be performing in 32-bit code. Rich
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