Date: Thu, 14 May 2015 12:25:39 +0200 From: Szabolcs Nagy <nsz@...t70.net> To: musl@...ts.openwall.com Subject: Re: [PATCH v3] Build process uses script to add CFI directives to x86 asm * Rich Felker <dalias@...c.org> [2015-05-13 22:57:20 -0400]: > 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. > yes, i think the line numbers would be wrong then the ; idea fixes it, but then .cfi should be in prefix position (because of comments) > > > 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? > i guess it could be tools/aswrap.sh $< $@ $(ARCH) -- $(CC) $(CFLAGS_ALL_STATIC) but it will be harder to follow what's going on in case of a failure than currently > > 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. > ok > > 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. > ok, they are the same
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