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50db00e136
Ksh handles local traps in virtual subshells the same way as local traps in ksh-style shell functions, which can cause incorrect operation. Reproducer script: trap 'echo "parent shell trap"; exit 0' USR1 (trap 'echo "subshell trap"' USR1; kill -USR1 $$) echo wrong Output on every ksh93 version: 'wrong' Output on every other shell: 'parent shell trap' The ksh93 output is wrong because $$ is the PID of the main shell, therefore 'kill -USR1 $$' from a subshell needs to issue SIGUSR1 to the main shell and trigger the 'echo SIGUSR1' trap. This is an inevitable consequence of processing signals in a virtual subshell. Signals are a process-wide property, but a virtual subshell and the parent shell share the same process. Therefore it is not possible to distinguish between the parent shell and subshell trap. This means virtual subshells are fundamentally incompatible with receiving signals. No workaround can make this work properly. Ksh could either assume the signal needs to be caught by the subshell trap (wrong in this case, but right in others) or by the parent shell trap. But it does neither and just gives up and does nothing, which I suppose is the least bad way of doing it wrong. As another example, consider a subshell that traps a signal, then passes its own process ID (as of9de65210, that's ${.sh.pid}) to another process to say "here is where to signal me". A virtual subshell will send it the PID that it shares with the the parent shell. Even if a virtual subshell receives the signal correctly, it may fork mid-execution afterwards, depending on the commands that it runs (and this varies by implementation as we fix or work around bugs). So its PID could be invalidated at any time. Forking a virtual subshell at the time of trapping a signal is the only way to ensure a persistent PID and correct operation. src/cmd/ksh93/bltins/trap.c: b_trap(): - Fork when trapping (or ignoring) a signal in a virtual subshell. (There's no need to fork when trapping a pseudosignal.) src/cmd/ksh93/tests/signal.sh: - Add tests. These are simplified versions of tests already there, which issued 'kill' as a background job. Currently, running a background job causes a virtual subshell to fork before forking the 'kill' background job (or *any* background job, seee3d7bf1d) -- an ugly partial workaround that I believe just became redundant and which I will remove in the next commit.
46 lines
2.5 KiB
C
46 lines
2.5 KiB
C
/***********************************************************************
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* *
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* This software is part of the ast package *
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* Copyright (c) 1982-2012 AT&T Intellectual Property *
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* Copyright (c) 2020-2022 Contributors to ksh 93u+m *
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* and is licensed under the *
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* Eclipse Public License, Version 1.0 *
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* by AT&T Intellectual Property *
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* *
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* A copy of the License is available at *
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* http://www.eclipse.org/org/documents/epl-v10.html *
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* (with md5 checksum b35adb5213ca9657e911e9befb180842) *
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* *
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* Information and Software Systems Research *
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* AT&T Research *
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* Florham Park NJ *
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* *
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* David Korn <dgk@research.att.com> *
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* *
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***********************************************************************/
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#include <releaseflags.h>
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#define SH_RELEASE_FORK "93u+m" /* only change if you develop a new ksh93 fork */
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#define SH_RELEASE_SVER "1.0.0-beta.2" /* semantic version number: https://semver.org */
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#define SH_RELEASE_DATE "2022-06-13" /* must be in this format for $((.sh.version)) */
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#define SH_RELEASE_CPYR "(c) 2020-2022 Contributors to ksh " SH_RELEASE_FORK
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/* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */
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/* Arithmetic $((.sh.version)) uses the last 10 chars, so the date must be at the end. */
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#if _AST_release
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# define SH_RELEASE SH_RELEASE_FORK "/" SH_RELEASE_SVER " " SH_RELEASE_DATE
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#else
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# ifdef _AST_git_commit
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# define SH_RELEASE SH_RELEASE_FORK "/" SH_RELEASE_SVER "+" _AST_git_commit " " SH_RELEASE_DATE
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# else
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# define SH_RELEASE SH_RELEASE_FORK "/" SH_RELEASE_SVER "+dev " SH_RELEASE_DATE
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# endif
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#endif
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/*
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* For shcomp: the version number (0-255) for the binary bytecode header.
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* Only increase very rarely, i.e.: if incompatible changes are made that
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* cause bytecode from newer versions to fail on older versions of ksh.
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*/
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#define SHCOMP_HDR_VERSION 5
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