libselinux: add patch to fix build with gcc < 4.7
This commit adds a patch from Hollis Blanchard on libselinux to fix build on host machines that have gcc < 4.7. Fixes: http://autobuild.buildroot.net/results/a82bb0c0b22ff24263ad7a7d165b21c0df7b3b1d/ Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
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From abe76789f8e7ce61b357f693eaed5b28feab5ce2 Mon Sep 17 00:00:00 2001
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From: Hollis Blanchard <hollis_blanchard@mentor.com>
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Date: Mon, 13 Aug 2018 12:11:33 -0700
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Subject: [PATCH] Fix build break around __atomic_*() with GCC<4.7
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The __atomic_* GCC primitives were introduced in GCC 4.7, but Red Hat
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Enterprise Linux 6.x (for example) provides GCC 4.4. Tweak the current code to
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use the (most conservative) __sync_synchronize() primitive provided by those
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older GCC versions.
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(Really, no __atomic or __sync operations are needed here at all, since POSIX
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4.12 "Memory Synchronization" says pthread_mutex_lock() and
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pthread_mutex_unlock() "synchronize memory with respect to other threads"...)
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Signed-off-by: Hollis Blanchard <hollis_blanchard@mentor.com>
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---
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libselinux/src/label_file.h | 18 ++++++++++++++++++
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1 file changed, 18 insertions(+)
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diff --git a/libselinux/src/label_file.h b/libselinux/src/label_file.h
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index 2fa85474..47859baf 100644
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--- a/libselinux/src/label_file.h
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+++ b/libselinux/src/label_file.h
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@@ -351,8 +351,14 @@ static inline int compile_regex(struct saved_data *data, struct spec *spec,
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* init_routine does not take a parameter, it's not possible
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* to use, so we generate the same effect with atomics and a
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* mutex */
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+#ifdef __ATOMIC_RELAXED
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regex_compiled =
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__atomic_load_n(&spec->regex_compiled, __ATOMIC_ACQUIRE);
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+#else
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+ /* GCC <4.7 */
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+ __sync_synchronize();
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+ regex_compiled = spec->regex_compiled;
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+#endif
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if (regex_compiled) {
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return 0; /* already done */
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}
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@@ -360,8 +366,14 @@ static inline int compile_regex(struct saved_data *data, struct spec *spec,
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__pthread_mutex_lock(&spec->regex_lock);
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/* Check if another thread compiled the regex while we waited
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* on the mutex */
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+#ifdef __ATOMIC_RELAXED
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regex_compiled =
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__atomic_load_n(&spec->regex_compiled, __ATOMIC_ACQUIRE);
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+#else
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+ /* GCC <4.7 */
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+ __sync_synchronize();
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+ regex_compiled = spec->regex_compiled;
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+#endif
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if (regex_compiled) {
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__pthread_mutex_unlock(&spec->regex_lock);
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return 0;
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@@ -404,7 +416,13 @@ static inline int compile_regex(struct saved_data *data, struct spec *spec,
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}
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/* Done. */
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+#ifdef __ATOMIC_RELAXED
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__atomic_store_n(&spec->regex_compiled, true, __ATOMIC_RELEASE);
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+#else
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+ /* GCC <4.7 */
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+ spec->regex_compiled = true;
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+ __sync_synchronize();
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+#endif
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__pthread_mutex_unlock(&spec->regex_lock);
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return 0;
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}
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--
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2.13.0
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