52 lines
1.9 KiB
Diff
52 lines
1.9 KiB
Diff
From c4dca1b9bca83b180138dfa4d7e5a65736cccb31 Mon Sep 17 00:00:00 2001
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From: Josh Stone <jistone@redhat.com>
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Date: Tue, 21 Jun 2016 16:06:09 -0700
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Subject: [PATCH] RTlib: use static TLS for the tramp guard (#99)
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With dynamic TLS, the call to __tls_get_addr() could reach additional
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instrumented code, infinitely recursing back to check the tramp guard.
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Static TLS is a limited resource, but this case in RTlib is special
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enough to warrant it for safety alone, nevermind performance.
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(cherry picked from commit 73cd0019856eca0636e652e402f9eaed6ba9dc61)
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Make the tramp guard bigger to avoid a glibc bug.
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Having just one byte of TLS induces glibc bug 14898 with the definition
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of FORCED_DYNAMIC_TLS_OFFSET. Bumping to two bytes avoids this.
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Fixes #101
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(cherry picked from commit d1b4334e13e7cc4a3ee52a34c9d3f63ebff129b2)
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---
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dyninstAPI_RT/src/RTcommon.c | 11 +++++++++--
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1 file changed, 9 insertions(+), 2 deletions(-)
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diff --git a/dyninstAPI_RT/src/RTcommon.c b/dyninstAPI_RT/src/RTcommon.c
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index ab125ff63f0e..f91ff12c943c 100644
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--- a/dyninstAPI_RT/src/RTcommon.c
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+++ b/dyninstAPI_RT/src/RTcommon.c
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@@ -117,10 +117,17 @@ int fakeTickCount;
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#if defined(_MSC_VER)
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#define TLS_VAR __declspec(thread)
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#else
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-#define TLS_VAR __thread
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+// Note, the initial-exec model gives us static TLS which can be accessed
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+// directly, unlike dynamic TLS that calls __tls_get_addr(). Such calls risk
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+// recursing back to us if they're also instrumented, ad infinitum. Static TLS
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+// must be used very sparingly though, because it is a limited resource.
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+// *** This case is very special -- do not use IE in general libraries! ***
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+#define TLS_VAR __thread __attribute__ ((tls_model("initial-exec")))
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#endif
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-TLS_VAR int DYNINST_tls_tramp_guard = 1;
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+// It's tempting to make this a char, but glibc < 2.17 hits a bug:
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+// https://sourceware.org/bugzilla/show_bug.cgi?id=14898
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+static TLS_VAR short DYNINST_tls_tramp_guard = 1;
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DLLEXPORT int DYNINST_lock_tramp_guard()
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{
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--
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2.7.4
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