From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tobias Bussmann <t.bussmann@gmx.net>
cc: John Naylor <johncnaylorls@gmail.com>, Lukas Fittl <lukas@fittl.com>,
        Jakob Egger <jakob@eggerapps.at>,
        pgsql-hackers <pgsql-hackers@postgresql.org>,
        Andres Freund <andres@anarazel.de>,
        Sandeep Thakkar <sandeep.thakkar@enterprisedb.com>
Subject: Re: Broken build on macOS (Universal / Intel): cpuid instruction not
 available
In-reply-to: <2943390.1780421880@sss.pgh.pa.us>
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Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Tue, 02 Jun 2026 13:38:00 -0400"
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Date: Wed, 03 Jun 2026 16:23:03 -0400
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I wrote:
> Also, the reason we manage to set USE_AVX2_WITH_RUNTIME_CHECK
> in a multi-arch build is that what configure actually tests
> is (a) is $host_cpu x86_64 and (b) does the compiler accept
> __attribute__((target("avx2"))).  On a multi-arch build,
> the ARM side spits out a warning
>   '+avx2' is not a recognized feature for this target (ignoring feature)
> but it doesn't actually fail, so configure thinks that's a success.

After further contemplation, I think the best fix for this problem
is to undo configure's mistake globally, not just in checksum.c.
checksum.c is the only file using USE_AVX2_WITH_RUNTIME_CHECK today,
but that might not be true forever.  Also, I think it's pure chance
that the test for that symbol succeeds in a universal build while
other similar tests don't.  So what the attached v2 does is to
#undef USE_AVX2_WITH_RUNTIME_CHECK as well as the USE_AVX512
symbols in c.h, if we're not in fact building for x86_64 hardware.
We could extend the list of things to #undef there later, if it
proves necessary.

The shape of this patch is partially dictated by not wanting to
create problems for Munro's pending patch [1], but I think it's
a reasonable solution even without that consideration.

			regards, tom lane

[1] https://www.postgresql.org/message-id/flat/CA%2BhUKGL8Hs-phHPugrWM%3D5=
dAkcT897rXyazYzLw-Szxnzgx-rA%40mail.gmail.com


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Content-Description: v2-fix-macos-universal-build.patch

diff --git a/src/include/c.h b/src/include/c.h
index 97ed8c63f5e..23db81fa7ca 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -1340,6 +1340,17 @@ typedef struct PGAlignedXLogBlock PGAlignedXLogBlock;
 #if (defined(__x86_64__) || defined(_M_AMD64))
 #define USE_SSE2
 
+#else							/* ! x86_64 */
+
+/*
+ * In "universal" macOS builds, it's possible for AVX-related symbols to
+ * get defined if the build host is x86_64, but we mustn't try to build
+ * that code when cross-compiling to aarch64.
+ */
+#undef USE_AVX2_WITH_RUNTIME_CHECK
+#undef USE_AVX512_CRC32C_WITH_RUNTIME_CHECK
+#undef USE_AVX512_POPCNT_WITH_RUNTIME_CHECK
+
 /*
  * We use the Neon instructions if the compiler provides access to them (as
  * indicated by __ARM_NEON) and we are on aarch64.  While Neon support is
@@ -1348,9 +1359,10 @@ typedef struct PGAlignedXLogBlock PGAlignedXLogBlock;
  * could not realistically use it there without a run-time check, which seems
  * not worth the trouble for now.
  */
-#elif defined(__aarch64__) && defined(__ARM_NEON)
+#if defined(__aarch64__) && defined(__ARM_NEON)
 #define USE_NEON
 #endif
+#endif							/* ! x86_64 */
 
 /* ----------------------------------------------------------------
  *				Section 9: system-specific hacks

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