Re: [PATCH] x86emul: rework wrapping of libc functions in test and fuzzing harnesses

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 17/08/2023 12:47 pm, Jan Beulich wrote:
> Our present approach is working fully behind the compiler's back. This
> was found to not work with LTO. Employ ld's --wrap= option instead. Note
> that while this makes the build work at least with new enough gcc (it
> doesn't with gcc7, for example, due to tool chain side issues afaict),
> according to my testing things still won't work when building the
> fuzzing harness with afl-cc: While with the gcc7 tool chain I see afl-as
> getting invoked, this does not happen with gcc13. Yet without using that
> assembler wrapper the resulting binary will look uninstrumented to
> afl-fuzz.
>
> While checking the resulting binaries I noticed that we've gained uses
> of snprintf() and strstr(), which only just so happen to not cause any
> problems. Add a wrappers for them as well.
>
> Since we don't have any actual uses of v{,sn}printf(), no definitions of
> their wrappers appear (just yet). But I think we want
> __wrap_{,sn}printf() to properly use __real_v{,sn}printf() right away,
> which means we need delarations of the latter.
>
> Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

This does resolve the build issue.  I do get a binary out of the end, so
Tested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>.  I presume that
you've smoke tested the resulting binary?

However, I do see something else in the logs which is concerning. 
Likely unrelated.

make[6]: Entering directory
'/builddir/build/BUILD/xen-4.18.0/tools/tests/x86_emulator'
gcc -m32 -march=i686 -DBUILD_ID -fno-strict-aliasing -std=gnu99 -Wall
-Wstrict-prototypes -Wdeclaration-after-statement
-Wno-unused-but-set-variable -Wno-unused-local-typedefs -g3 -Werror -Og
-fno-omit-frame-pointer
-D__XEN_INTERFACE_VERSION__=__XEN_LATEST_INTERFACE_VERSION__
-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -mno-tls-direct-seg-refs
-fno-pie -fno-stack-protector -fno-exceptions
-fno-asynchronous-unwind-tables -fno-builtin -g0 -D_64f2 -mavx512fp16
-ffixed-xmm0 -Os -DVEC_SIZE=64 -DFLOAT_SIZE=2 -c avx512fp16.c
make[6]: Leaving directory
'/builddir/build/BUILD/xen-4.18.0/tools/tests/x86_emulator'
/tmp/ccrznrqa.s: Assembler messages:
/tmp/ccrznrqa.s:98: Error: no such instruction: `vmovw .LC0,%xmm3'
/tmp/ccrznrqa.s:99: Error: no such instruction: `vmovw %xmm3,58(%esp)'
/tmp/ccrznrqa.s:105: Error: no such instruction: `vcvtsi2shl
%eax,%xmm1,%xmm1'
/tmp/ccrznrqa.s:106: Error: no such instruction: `vmovw
%xmm3,382(%esp,%eax,2)'
/tmp/ccrznrqa.s:107: Error: no such instruction: `vmovw
%xmm1,-2(%edx,%eax,2)'
/tmp/ccrznrqa.s:108: Error: no such instruction: `vcvtsi2shl
%ecx,%xmm1,%xmm1'
/tmp/ccrznrqa.s:109: Error: no such instruction: `vmovw
%xmm1,318(%esp,%eax,2)'
/tmp/ccrznrqa.s:113: Error: no such instruction: `vaddph
256(%esp),%zmm7,%zmm5'
<snip many>
simd-fma.c:208: Error: no such instruction: `vfmaddsub231ph
60(%esp){1to32},%zmm6,%zmm5'
simd-fma.c:209: Error: no such instruction: `vfmaddsub231ph
60(%esp){1to32},%zmm6,%zmm1'

GCC is 12.2.1, binutils is 2.37

AVX512_FP16 was added in bintuils 2.38 so I understand the simd-fma.c
complains, but ccrznrqa.s suggest that there's a bad -m passed.  I
haven't figured out which source file it logically associated with.

~Andrew