diff mbox

Fix documentation about rot agent expression bytecode

Message ID 1500477367-28117-1-git-send-email-simon.marchi@ericsson.com
State New, archived
Headers

Commit Message

Simon Marchi July 19, 2017, 3:16 p.m. UTC 
  The rot agent expression bytecode rotates the three items on the top of
the stack.  It is not clear which way the rotation is.  However, the
documentation currently shows this as the effect of the instructions:

   a b c => c b a

which doesn't make sense, since the value b doesn't move.  The two
valid possibilities I see are

  a b c => b c a
  a b c => c a b

depending on which way you rotate.

When looking at the gdbserver code, the top of the stack becomes the
third item, and the next-to-top item becomes the top.  So the second
form would be the right one, since in this notation the top of the stack
is the rightmost element:

  a b c => c a b

I adjusted the symbolic description and added a bit of text to make it
more obvious.

gdb/doc/ChangeLog:

	* agentexpr.texi (rot): Fix symbolic description, improve
	textual description.
---
 gdb/doc/agentexpr.texi | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
diff mbox

Patch

diff --git a/gdb/doc/agentexpr.texi b/gdb/doc/agentexpr.texi
index 5668e9c..aef1973 100644
--- a/gdb/doc/agentexpr.texi
+++ b/gdb/doc/agentexpr.texi
@@ -396,8 +396,10 @@  is zero, this is the same as @code{dup}; if @var{n} is one, it copies
 the item under the top item, etc.  If @var{n} exceeds the number of
 items on the stack, terminate with an error.
 
-@item @code{rot} (0x33): @var{a} @var{b} @var{c} => @var{c} @var{b} @var{a}
-Rotate the top three items on the stack.
+@item @code{rot} (0x33): @var{a} @var{b} @var{c} => @var{c} @var{a} @var{b}
+Rotate the top three items on the stack.  The top (first) item becomes
+the third item, the next-to-top (second) item becomes the top (first) item
+and the third item becomes the next-to-top (second) item.
 
 @item @code{if_goto} (0x20) @var{offset}: @var{a} @result{}
 Pop an integer off the stack; if it is non-zero, branch to the given