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* Re: c/3414: Inaccurate documentation of __attribute__((malloc))
@ 2003-03-27 21:04 neroden
0 siblings, 0 replies; 3+ messages in thread
From: neroden @ 2003-03-27 21:04 UTC (permalink / raw)
To: bje, gcc-bugs, gcc-prs, h.b.furuseth
Synopsis: Inaccurate documentation of __attribute__((malloc))
State-Changed-From-To: open->analyzed
State-Changed-By: neroden
State-Changed-When: Thu Mar 27 21:01:26 2003
State-Changed-Why:
Analyzed indeed.
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=3414
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: c/3414: Inaccurate documentation of __attribute__((malloc))
@ 2003-02-18 2:54 bje
0 siblings, 0 replies; 3+ messages in thread
From: bje @ 2003-02-18 2:54 UTC (permalink / raw)
To: bje, gcc-bugs, gcc-prs, h.b.furuseth, nobody
Synopsis: Inaccurate documentation of __attribute__((malloc))
Responsible-Changed-From-To: unassigned->bje
Responsible-Changed-By: bje
Responsible-Changed-When: Tue Feb 18 02:54:08 2003
Responsible-Changed-Why:
Got it.
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=3414
^ permalink raw reply [flat|nested] 3+ messages in thread
* c/3414: Inaccurate documentation of __attribute__((malloc))
@ 2001-06-25 13:36 Hallvard B Furuseth
0 siblings, 0 replies; 3+ messages in thread
From: Hallvard B Furuseth @ 2001-06-25 13:36 UTC (permalink / raw)
To: gcc-gnats; +Cc: h.b.furuseth
>Number: 3414
>Category: c
>Synopsis: Inaccurate documentation of __attribute__((malloc))
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: unassigned
>State: open
>Class: doc-bug
>Submitter-Id: net
>Arrival-Date: Mon Jun 25 13:36:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator: Hallvard B Furuseth
>Release: 3.0
>Organization:
>Environment:
System: SunOS bombur.uio.no 5.8 Generic_108528-03 sun4u sparc SUNW,Ultra-5_10
Architecture: sun4
host: sparc-sun-solaris2.8
build: sparc-sun-solaris2.8
target: sparc-sun-solaris2.8
configured with: ./configure --quiet --enable-version-specific-runtime-libs --prefix=/usit/bombur/hbf --program-suffix=-3.0
>Description:
From @item malloc, @node Function Attributes:
"The `malloc' attribute is used to tell the compiler that a
function may be treated as if it were the malloc function."
The compiler could assume several things about that; e.g.
that the return value will be aligned for any data type.
However, the rest of the paragraph is:
"The compiler assumes that calls to malloc result in a
pointers that cannot alias anything. This will often
improve optimization."
Is this the *only* assumption __attribute__((malloc)) causes?
Incidentally, it also assumes that the program uses malloc
correctly - here is a malloc which _can_ alias something:
free(x = malloc(10));
if (x == (y = malloc(10))) { ... }
(BTW, typo: "a pointers" should be "a pointer".
>How-To-Repeat:
>Fix:
I'm guessing that you mean something like this, but I
have not checked. Sorry if my English is a bit clumsy:
The @code{malloc} attribute is used to tell the compiler
that a function returns a pointer which cannot alias
anything (or a null pointer), i.e. i behaves like the
@code{malloc} function. This will often improve
optimization.
Note that this may break programs that incorrectly uses
the value of such a pointer after it has been
invalidated (in the case of malloced pointers by calling
@code{free()}, even if the pointer is not dereferenced.
>Release-Note:
>Audit-Trail:
>Unformatted:
^ permalink raw reply [flat|nested] 3+ messages in thread
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2003-03-27 21:04 c/3414: Inaccurate documentation of __attribute__((malloc)) neroden
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2003-02-18 2:54 bje
2001-06-25 13:36 Hallvard B Furuseth
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