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* [glibc/maskray/clang] i386: Explain why __HAVE_64B_ATOMICS has to be 0
@ 2021-11-02 20:00 Fangrui Song
  0 siblings, 0 replies; only message in thread
From: Fangrui Song @ 2021-11-02 20:00 UTC (permalink / raw)
  To: glibc-cvs

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=cca75bd8b53b82d80299b03b368355b158832c9a

commit cca75bd8b53b82d80299b03b368355b158832c9a
Author: Florian Weimer <fweimer@redhat.com>
Date:   Tue Nov 2 10:26:23 2021 +0100

    i386: Explain why __HAVE_64B_ATOMICS has to be 0

Diff:
---
 sysdeps/x86/atomic-machine.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sysdeps/x86/atomic-machine.h b/sysdeps/x86/atomic-machine.h
index 695222e4fa..2692d94a92 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"


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