Thomas Klausner
2014-05-31 13:23:38 UTC
Is someone looking at this yet?
The submitter reports it's breaking git, which sounds like it
should be fixed quickly.
Thomas
Architecture: x86_64
Machine: amd64
Evaluation of commands goes completely haywire if a file containing
a break/continue/return command outside its "intended" scope is sourced
using a dot command inside its "intended" scope. The main symptom is
not exiting from the sourced file when supposed to, leading to evaluation
of commands that were not supposed to be evaluated. A secondary symptom
is that these extra commands are not evaluated correctly, as some of them
are skipped. Some examples are listed in the How-To-Repeat section.
According to the POSIX standard, this is how it should work:
dot:
The shell shall execute commands from the file in the current
environment.
break:
The break utility shall exit from the smallest enclosing for, while,
or until loop, [...]
continue:
The continue utility shall return to the top of the smallest
enclosing for, while, or until loop, [...]
return:
The return utility shall cause the shell to stop executing
the current function or dot script. If the shell is not currently
executing a function or dot script, the results are unspecified.
It is clear that return should return from a sourced file, which
it does not do. Whether break and continue should work from the sourced
file might be debatable. Because the dot command says "in the current
environment", I'd say yes. In any case, it should not fail in weird
ways like it does now!
The problems occur with return (a) and break/continue (b) because:
1) dotcmd() does not record the function nesting level prior to
sourcing the file nor does it touch the loopnest variable,
leading to either
2 a) returncmd() being unable to detect that it should not set
evalskip to SKIPFUNC but SKIPFILE, or
b) breakcmd() setting evalskip to SKIPCONT or SKIPBREAK,
leading to
3) cmdloop() not detecting that it should skip the rest of
the file, due to only checking for SKIPFILE.
The result is that cmdloop() keeps executing lines from the file
whilst evalskip is set, which is the main symptom. Because
evalskip is checked in multiple places in eval.c, the secondary
symptom appears.
Run the following script:
printf "break\necho break1; echo break2" >break
printf "continue\necho continue1; echo continue2" >continue
printf "return\necho return1; echo return2" >return
while true; do . ./break; done
for i in 1 2; do . ./continue; done
func() {
. ./return
}
func
No output should be produced, but instead this is the result:
break1
continue1
continue1
return1
The main symptom is evident from the unexpected output and the secondary
one from the fact that there are no lines with '2' in them.
Here is patch to src/bin/sh to fix the above problems. It keeps
track of the function nesting level at the beginning of a dot command
to enable the return command to work properly.
I also changed the undefined-by-standard functionality of the return
command when it's not in a dot command or function from (indirectly)
exiting the shell to being silently ignored. This was done because
the previous way has at least one bug: the shell exits without asking
for confirmation when there are stopped jobs.
Because I read the standard to mean that break and continue should have
an effect outside the sourced file, that's how I implemented it. For what
it's worth, this also seems to be what bash does. Also laziness, because
this way required no changes to loopnesting tracking. If this is not
wanted, it might make sense to move the nesting tracking to the inputfile
stack.
The patch also does some clean-up to reduce the amount of global
variables by moving the dotcmd() and the find_dot_file() functions from
main.c to eval.c and making in_function() a proper function.
[patch excised]
----- End forwarded message -----
The submitter reports it's breaking git, which sounds like it
should be fixed quickly.
Thomas
Number: 48843
Category: bin
Synopsis: dot commands mess up scope nesting tracking
Confidential: no
Severity: serious
Priority: medium
Responsible: bin-bug-people
State: open
Class: sw-bug
Submitter-Id: net
Arrival-Date: Wed May 28 23:10:00 +0000 2014
Originator: Jarmo Jaakkola
Release: NetBSD 6.1.2_PATCH
System: NetBSD kotoisa.roskakori.fi 6.1.2_PATCH NetBSD 6.1.2_PATCH (KOTOISA) #5: Mon Jan 20 17:01:44 EET 2014 ***@kotoisa.roskakori.fi:/usr/src/sys/arch/amd64/compile/KOTOISA amd64Category: bin
Synopsis: dot commands mess up scope nesting tracking
Confidential: no
Severity: serious
Priority: medium
Responsible: bin-bug-people
State: open
Class: sw-bug
Submitter-Id: net
Arrival-Date: Wed May 28 23:10:00 +0000 2014
Originator: Jarmo Jaakkola
Release: NetBSD 6.1.2_PATCH
Architecture: x86_64
Machine: amd64
Evaluation of commands goes completely haywire if a file containing
a break/continue/return command outside its "intended" scope is sourced
using a dot command inside its "intended" scope. The main symptom is
not exiting from the sourced file when supposed to, leading to evaluation
of commands that were not supposed to be evaluated. A secondary symptom
is that these extra commands are not evaluated correctly, as some of them
are skipped. Some examples are listed in the How-To-Repeat section.
According to the POSIX standard, this is how it should work:
dot:
The shell shall execute commands from the file in the current
environment.
break:
The break utility shall exit from the smallest enclosing for, while,
or until loop, [...]
continue:
The continue utility shall return to the top of the smallest
enclosing for, while, or until loop, [...]
return:
The return utility shall cause the shell to stop executing
the current function or dot script. If the shell is not currently
executing a function or dot script, the results are unspecified.
It is clear that return should return from a sourced file, which
it does not do. Whether break and continue should work from the sourced
file might be debatable. Because the dot command says "in the current
environment", I'd say yes. In any case, it should not fail in weird
ways like it does now!
The problems occur with return (a) and break/continue (b) because:
1) dotcmd() does not record the function nesting level prior to
sourcing the file nor does it touch the loopnest variable,
leading to either
2 a) returncmd() being unable to detect that it should not set
evalskip to SKIPFUNC but SKIPFILE, or
b) breakcmd() setting evalskip to SKIPCONT or SKIPBREAK,
leading to
3) cmdloop() not detecting that it should skip the rest of
the file, due to only checking for SKIPFILE.
The result is that cmdloop() keeps executing lines from the file
whilst evalskip is set, which is the main symptom. Because
evalskip is checked in multiple places in eval.c, the secondary
symptom appears.
Run the following script:
printf "break\necho break1; echo break2" >break
printf "continue\necho continue1; echo continue2" >continue
printf "return\necho return1; echo return2" >return
while true; do . ./break; done
for i in 1 2; do . ./continue; done
func() {
. ./return
}
func
No output should be produced, but instead this is the result:
break1
continue1
continue1
return1
The main symptom is evident from the unexpected output and the secondary
one from the fact that there are no lines with '2' in them.
Here is patch to src/bin/sh to fix the above problems. It keeps
track of the function nesting level at the beginning of a dot command
to enable the return command to work properly.
I also changed the undefined-by-standard functionality of the return
command when it's not in a dot command or function from (indirectly)
exiting the shell to being silently ignored. This was done because
the previous way has at least one bug: the shell exits without asking
for confirmation when there are stopped jobs.
Because I read the standard to mean that break and continue should have
an effect outside the sourced file, that's how I implemented it. For what
it's worth, this also seems to be what bash does. Also laziness, because
this way required no changes to loopnesting tracking. If this is not
wanted, it might make sense to move the nesting tracking to the inputfile
stack.
The patch also does some clean-up to reduce the amount of global
variables by moving the dotcmd() and the find_dot_file() functions from
main.c to eval.c and making in_function() a proper function.
[patch excised]
----- End forwarded message -----