From: Florian Weimer <fweimer@redhat.com>
Date: Tue, 2 Nov 2021 09:26:23 +0000 (+0100)
Subject: i386: Explain why __HAVE_64B_ATOMICS has to be 0
X-Git-Tag: glibc-2.35~365
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=cca75bd8b53b82d80299b03b368355b158832c9a;p=thirdparty%2Fglibc.git

i386: Explain why __HAVE_64B_ATOMICS has to be 0
---

diff --git a/sysdeps/x86/atomic-machine.h b/sysdeps/x86/atomic-machine.h
index 695222e4faa..2692d94a929 100644
--- a/sysdeps/x86/atomic-machine.h
+++ b/sysdeps/x86/atomic-machine.h
@@ -60,6 +60,10 @@ typedef uintmax_t uatomic_max_t;
 # define BR_CONSTRAINT			"q"
 # define IBR_CONSTRAINT			"iq"
 #else
+/* Since the Pentium, i386 CPUs have supported 64-bit atomics, but the
+   i386 psABI supplement provides only 4-byte alignment for uint64_t
+   inside structs, so it is currently not possible to use 64-bit
+   atomics on this platform.  */
 # define __HAVE_64B_ATOMICS		0
 # define SP_REG				"esp"
 # define SEG_REG			"gs"