[Buildroot] [PATCH] package/binutils: prevent selecting 2.37 for AVX512 systems

* [Buildroot] [PATCH] package/binutils: prevent selecting 2.37 for AVX512 systems
@ 2022-10-26 17:54 Thomas Petazzoni via buildroot
  2022-10-30 19:33 ` Yann E. MORIN
  0 siblings, 1 reply; 2+ messages in thread
From: Thomas Petazzoni via buildroot @ 2022-10-26 17:54 UTC (permalink / raw)
  To: buildroot; +Cc: Romain Naour, Giulio Benetti, Yann E. MORIN, Thomas Petazzoni

Support for the AVX512FP16 instructions was added in binutils
2.38. See the binutils 2.38 releases notes [0] that state:

    X86:
    [...]
      * Add support for Intel AVX512_FP16 instructions.

[0] https://sourceware.org/pipermail/binutils/2022-February/119721.html

It turns out that when building GCC 12.x, some of these AVX512FP16
instructions are now used, and therefore when binutils < 2.38 is used,
the build fails as the assembler does not recognize those
instructions:

/tmp/ccChzL2g.s: Assembler messages:
/tmp/ccChzL2g.s:20: Error: no such instruction: `vmovw 24(%esp),%xmm2'
/tmp/ccChzL2g.s:21: Error: no such instruction: `vmovw 28(%esp),%xmm3'
/tmp/ccChzL2g.s:22: Error: no such instruction: `vmovw 32(%esp),%xmm4'
/tmp/ccChzL2g.s:23: Error: no such instruction: `vmovw 36(%esp),%xmm5'
/tmp/ccChzL2g.s:30: Error: no such instruction: `vcvtsh2ss %xmm2,%xmm6,%xmm6'
/tmp/ccChzL2g.s:36: Error: no such instruction: `vcvtsh2ss %xmm3,%xmm6,%xmm6'
/tmp/ccChzL2g.s:42: Error: no such instruction: `vcvtsh2ss %xmm4,%xmm7,%xmm7'
/tmp/ccChzL2g.s:48: Error: no such instruction: `vcvtsh2ss %xmm5,%xmm1,%xmm1'
/tmp/ccChzL2g.s:80: Error: no such instruction: `vcvtss2sh (%esp),%xmm1,%xmm1'
/tmp/ccChzL2g.s:96: Error: no such instruction: `vcvtss2sh (%esp),%xmm0,%xmm0'
/tmp/ccChzL2g.s:100: Error: no such instruction: `vucomish %xmm1,%xmm1'
/tmp/ccChzL2g.s:103: Error: no such instruction: `vucomish %xmm0,%xmm0'
/tmp/ccChzL2g.s:122: Error: no such instruction: `vucomish %xmm2,%xmm2'

The same issue does not occur with GCC 11.x, but nothing prevents
other packages than GCC to use those instructions, so the problem
really lies on the binutils side missing the support for those
instructions.

Also, in Buildroot, we do not distinguish AVX512 in general from
AVX512FP16 specifically, so our only option is to make binutils 2.37
unavailable for AVX512 systems even if some of them perhaps don't
support AVX512FP16 anyway. This seems like a reasonable trade-off, as
binutils 2.38 is anyway already the default in Buildroot, and
AVX512-capable systems are fairly recent, and therefore using a recent
binutils version should not be a problem on these platforms.

Fixes:

  http://autobuild.buildroot.net/results/eb6e28c934654e6d714973415a2fb452f9580279/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
---
 package/binutils/Config.in.host | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/package/binutils/Config.in.host b/package/binutils/Config.in.host
index 51802db043..5dd2af2f9c 100644
--- a/package/binutils/Config.in.host
+++ b/package/binutils/Config.in.host
@@ -14,6 +14,9 @@ choice
 
 config BR2_BINUTILS_VERSION_2_37_X
 	bool "binutils 2.37"
+	# AVX512FP16 instructions were not supported before binutils
+	# 2.38
+	depends on !BR2_X86_CPU_HAS_AVX512
 
 config BR2_BINUTILS_VERSION_2_38_X
 	bool "binutils 2.38"
-- 
2.37.3

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