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Re: [PATCH] x86emul: fix test harness build for gas 2.36

  • To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Mon, 19 Apr 2021 16:41:20 +0100
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On 19/04/2021 16:30, Jan Beulich wrote:
> All of the sudden, besides .text and .rodata and alike, an always
> present .note.gnu.property section has appeared. This section, when
> converting to binary format output, gets placed according to its
> linked address, causing the resulting blobs to be about 128Mb in size.
> The resulting headers with a C representation of the binary blobs then
> are, of course all a multiple of that size (and take accordingly long
> to create). I didn't bother waiting to see what size the final
> test_x86_emulator binary then would have had.
> See also https://sourceware.org/bugzilla/show_bug.cgi?id=27753.
> Rather than figuring out whether gas supports -mx86-used-note=, simply
> remove the section while creating *.bin.
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> --- a/tools/tests/x86_emulator/testcase.mk
> +++ b/tools/tests/x86_emulator/testcase.mk
> @@ -12,11 +12,11 @@ all: $(TESTCASE).bin
>  %.bin: %.c
>       $(CC) $(filter-out -M% .%,$(CFLAGS)) -c $<
>       $(LD) $(LDFLAGS_DIRECT) -N -Ttext 0x100000 -o $*.tmp $*.o
> -     $(OBJCOPY) -O binary $*.tmp $@
> +     $(OBJCOPY) -O binary -R .note.gnu.property $*.tmp $@
>       rm -f $*.tmp
>  %-opmask.bin: opmask.S
>       $(CC) $(filter-out -M% .%,$(CFLAGS)) -c $< -o $(basename $@).o
>       $(LD) $(LDFLAGS_DIRECT) -N -Ttext 0x100000 -o $(basename $@).tmp 
> $(basename $@).o
> -     $(OBJCOPY) -O binary $(basename $@).tmp $@
> +     $(OBJCOPY) -O binary -R .note.gnu.property $(basename $@).tmp $@
>       rm -f $(basename $@).tmp

Hmm - this is very ugly.  We don't really want to be stripping this
information, because it covers various properties of the binary which
need not to be lost, including stack-clash mitigations, and CET status.

We might be able to get away with saying that we're operating strictly
with defaults, and folding these *.bin's back into a program which is
also linked with defaults, at which point the resulting binary ought to
end up with a compatible .note.gnu.property section, but I'm not sure
how convinced I am by this argument.




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