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gdb/doc: extend the documentation of the jump command

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This commit addresses PR gdb/7946.  While checking for bugs relating
to the jump command I noticed a long standing bug that points out a
deficiency with GDB's documentation of the jump command.

The bug points out that 'jump 0x...' is not always the same as 'set
$pc = 0x...' and then 'continue'.  Writing directly to the $pc
register does not update any auxiliary state, e.g. $npc on SPARC,
while using 'jump' does.

It felt like this would be an easy issue to address by adding a
paragraph to the docs, so I took a stab at writing something suitable.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=7946

Approved-By: Eli Zaretskii <eliz@gnu.org>
This commit is contained in:
Andrew Burgess 2023-04-24 15:27:27 +01:00
parent 08ec06d644
commit 0d42948f0c
1 changed files with 8 additions and 0 deletions
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gdb/doc/gdb.texinfo
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@ -20618,6 +20618,14 @@ makes the next @code{continue} command or stepping command execute at
address @code{0x485}, rather than at the address where your program stopped.
@xref{Continuing and Stepping, ,Continuing and Stepping}.
However, writing directly to @code{$pc} will only change the value of
the program-counter register, while using @code{jump} will ensure that
any additional auxiliary state is also updated. For example, on
SPARC, @code{jump} will update both @code{$pc} and @code{$npc}
registers prior to resuming execution. When using the approach of
writing directly to @code{$pc} it is your job to also update the
@code{$npc} register.
The most common occasion to use the @code{jump} command is to back
up---perhaps with more breakpoints set---over a portion of a program
that has already executed, in order to examine its execution in more