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From: "Jan Beulich" <JBeulich@suse.com>
To: "xen-devel" <xen-devel@lists.xenproject.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>, WeiLiu <wl@xen.org>,
	Roger Pau Monne <roger.pau@citrix.com>
Subject: [Xen-devel] [PATCH 2/2] x86/traps: widen condition for logging top-of-stack
Date: Fri, 31 May 2019 03:22:12 -0600
Message-ID: <5CF0F2440200007800233D84@prv1-mh.provo.novell.com> (raw)
Message-ID: <20190531092212.X-cCoZ073jZO7fUfXPnrOMHRk3cx9V2FavYOhuE7nCY@z> (raw)
In-Reply-To: <5CF0ECE80200007800233D41@prv1-mh.provo.novell.com>

Despite -fno-omit-frame-pointer the compiler may omit the frame pointer,
often for relatively simple leaf functions. (To give a specific example,
the case I've run into this with is _pci_hide_device() and gcc 8.
Interestingly the even more simple neighboring iommu_has_feature() does
get a frame pointer set up, around just a single instruction. But this
may be a result of the size-of-asm() effects discussed elsewhere.)

Log the top-of-stack value if it looks valid _or_ if RIP looks invalid.

Also annotate non-frame-pointer-based stack trace entries with a
question mark, to signal clearly that any one of them may not actually
be part of the call stack.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -431,7 +431,7 @@ static void _show_trace(unsigned long sp
     {
         addr = *stack++;
         if ( is_active_kernel_text(addr) )
-            printk("   [<%p>] %pS\n", _p(addr), _p(addr));
+            printk("   [<%p>] ? %pS\n", _p(addr), _p(addr));
     }
 }
 
@@ -502,21 +502,25 @@ static void show_trace(const struct cpu_
     if ( is_active_kernel_text(regs->rip) ||
          !is_active_kernel_text(tos) )
         printk("   [<%p>] %pS\n", _p(regs->rip), _p(regs->rip));
+
+    if ( !sp )
+        return;
+
     /*
-     * Else RIP looks bad but the top of the stack looks good.  Perhaps we
-     * followed a wild function pointer? Lets assume the top of the stack is a
+     * If RIP looks bad or the top of the stack looks good, log the top of
+     * stack as well.  Perhaps we followed a wild function pointer, or we're
+     * in a function without frame pointer, or in a function prologue before
+     * the frame pointer gets set up? Lets assume the top of the stack is a
      * return address; print it and skip past so _show_trace() doesn't print
      * it again.
      */
-    else if ( sp )
+    if ( !is_active_kernel_text(regs->rip) ||
+         is_active_kernel_text(tos) )
     {
-        printk("   [<%p>] %pS\n", _p(tos), _p(tos));
+        printk("   [<%p>] ? %pS\n", _p(tos), _p(tos));
         sp++;
     }
 
-    if ( !sp )
-        return;
-
     _show_trace((unsigned long)sp, regs->rbp);
 
     printk("\n");





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  parent reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-31  8:59 [PATCH 0/2]: x86/traps: improve show_trace()'s top-of-stack handling Jan Beulich
2019-05-31  8:59 ` [Xen-devel] " Jan Beulich
2019-05-31  9:17 ` [PATCH 1/2] x86/traps: guard top-of-stack reads Jan Beulich
2019-05-31  9:17   ` [Xen-devel] " Jan Beulich
2019-06-07 17:51   ` Andrew Cooper
2019-06-11  9:57     ` Jan Beulich
2019-05-31  9:22 ` Jan Beulich [this message]
2019-05-31  9:22   ` [Xen-devel] [PATCH 2/2] x86/traps: widen condition for logging top-of-stack Jan Beulich
2019-06-07 18:01   ` Andrew Cooper
2019-06-11  9:46     ` Jan Beulich
2019-06-17  8:10 ` [Xen-devel] [PATCH v2 0/2]: x86/traps: improve show_trace()'s top-of-stack handling Jan Beulich
2019-06-17  8:12   ` [Xen-devel] [PATCH v2 1/2] x86/traps: guard top-of-stack reads Jan Beulich
2019-07-02 17:47     ` Andrew Cooper
2019-07-03  7:10       ` Jan Beulich
2019-06-17  8:13   ` [Xen-devel] [PATCH v2 2/2] x86/traps: widen condition for logging top-of-stack Jan Beulich
2019-07-03 10:21     ` Andrew Cooper
2019-07-03 10:34       ` Jan Beulich
2019-07-03 19:47         ` Andrew Cooper
2019-07-04  9:09           ` Jan Beulich

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