View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0000386 | 1003.1(2008)/Issue 7 | System Interfaces | public | 2011-02-22 23:58 | 2013-04-16 13:06 |
| Reporter | eblake | Assigned To | ajosey | ||
| Priority | normal | Severity | Objection | Type | Enhancement Request |
| Status | Closed | Resolution | Accepted As Marked | ||
| Name | Eric Blake | ||||
| Organization | Red Hat | ||||
| User Reference | ebb.environ | ||||
| Section | 2.2.2 The Name Space | ||||
| Page Number | 469 | ||||
| Line Number | 15936 | ||||
| Interp Status | --- | ||||
| Final Accepted Text | See 0000386:0000721 | ||||
| Summary | 0000386: environ should be declared in <unistd.h> | ||||
| Description | The standard appears to be ambiguous - XBD <unistd.h> does not list environ, but XSH exec (line 25687) implies that #include <unistd.h> will provide the declaration, rather than documenting the burden on the application to declare it. Meanwhile, many implementations already declare environ in <unistd.h> (possibly when requesting extensions to the standard), and it seems awkward to require special-case treatment for environ. This proposal changes things to remove the special casing. If my Desired Action is not taken as-is, then we should at least update the wording in XSH exec to make it explicit that the user must declare the variable themselves (in fact, such wording might be useful in TC1, while delaying this proposal to issue 8). | ||||
| Desired Action | At line 15126 [XBD <unistd.h>], insert: extern char **environ; At line 15936 [XSH 2.2.2 The Name Space], delete ", except environ,". At line 26007 [XSH exec APPLICATION USAGE], add a paragraph: Older versions of this standard required that applications provide the declaration: extern char **environ; before using environ, since no standard header was required to provide it. Code may safely keep such a declaration, even though this version of the standard now requires <unistd.h> to declare environ. | ||||
| Tags | tc1-2008 | ||||
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There is also the environ pointer page to consider (page 763), which has no mention of <unistd.h> in the synopsis. |
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There are several warnings in the standard that using environ in a multithreaded application causes undefined behavior as well as statements that environ is not defined in any header (and the reasons why this is the intended behavior of the standard). See XSH 2.2.2 (The Name Space) P469, L15936; 2.9.1 (Thread Safety) P508, L17516; XSH exec DESCRIPTION P772, L25713; XSH exec APPLICATION USAGE P779, L25989; XSH exec RATIONALE P781, L26059-26060; XSH getenv() DESCRIPTION P1008, L33856; XSH getenv() RATIONALE P1008-1009, L33880-33897; XSH setenv() DESCRIPTION P99347-99348; XSH unsetenv() DESCRIPTION P2161, L68256-68257; XRAT A.8.1 (Environment Variable Definition) P3467, L116537-116540 for examples of why environ should not be defined in any header and the user should be required to define environ if it is going to be used instead of the preferred getenv(), setenv(), and putenv() functions. I believe this change should be rejected. |
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See 0000167 - TC1 is changing things to state that modification of the array pointed to by environ, or of an entry in the array pointed to by environ, is not multi-thread safe, but that reading environ in order to initialize a const **char pointer to walk through and read the array, as well as assignment to environ, _is_ safe, even in a multi-threaded application. Therefore, your fears about accessing environ are unfounded, and there no longer exists a reason to hide environ from being declared. |
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At line 25708, change "In addition, the following variable:" to "In addition, the following variable, which must be declared by the user if it is to be used directly:" |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 2011-02-22 23:58 | eblake | New Issue | |
| 2011-02-22 23:58 | eblake | Status | New => Under Review |
| 2011-02-22 23:58 | eblake | Assigned To | => ajosey |
| 2011-02-22 23:58 | eblake | Name | => Eric Blake |
| 2011-02-22 23:58 | eblake | Organization | => Red Hat |
| 2011-02-22 23:58 | eblake | User Reference | => ebb.environ |
| 2011-02-22 23:58 | eblake | Section | => 2.2.2 The Name Space |
| 2011-02-22 23:58 | eblake | Page Number | => 469 |
| 2011-02-22 23:58 | eblake | Line Number | => 15936 |
| 2011-02-22 23:58 | eblake | Interp Status | => --- |
| 2011-02-23 11:49 | geoffclare | Note Added: 0000677 | |
| 2011-02-23 19:47 | Don Cragun | Note Added: 0000678 | |
| 2011-02-23 20:25 | eblake | Relationship added | related to 0000167 |
| 2011-02-23 20:26 | eblake | Note Added: 0000679 | |
| 2011-03-24 16:20 | nick | Note Added: 0000721 | |
| 2011-03-24 16:20 | nick | Status | Under Review => Resolved |
| 2011-03-24 16:20 | nick | Resolution | Open => Accepted As Marked |
| 2011-03-24 16:21 | nick | Final Accepted Text | => See 0000386:0000721 |
| 2011-03-24 16:21 | nick | Tag Attached: tc1-2008 | |
| 2013-04-16 13:06 | ajosey | Status | Resolved => Closed |
| 2019-04-16 07:38 | geoffclare | Relationship added | has duplicate 0001246 |
