The following issue has been SUBMITTED.
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http://austingroupbugs.net/view.php?id=1153
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Reported By: Villemoes
Assigned To: ajosey
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Project: 1003.1(2008)/Issue 7
Issue ID: 1153
Category: System Interfaces
Type: Clarification Requested
Severity: Editorial
Priority: normal
Status: Under Review
Name: Rasmus Villemoes
Organization:
User Reference:
Section: fmemopen
Page Number:
Line Number:
Interp Status: ---
Final Accepted Text:
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Date Submitted: 2017-06-22 08:02 UTC
Last Modified: 2017-06-22 08:02 UTC
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Summary: fread/fwrite to/from buffer underlying the memory
stream
Description:
In glibc, running the code below under valgrind gives a
Source and destination overlap in memcpy
Without the setvbuf calls, this doesn't trigger because the reads and
writes happen via an internal buffer.
I cannot find anything that says the application cannot do fread/fwrite
calls on a memory stream, using part of the stream's underlying buffer as
destination/source.
<pre>
#include <stdio.h>
int main(int argc, char *argv[])
{
char x[4] = "123";
char y[4] = "abc";
FILE *f = fmemopen(x, 3, "r");
FILE *g = fmemopen(y, 3, "w");
setvbuf(f, NULL, _IONBF, 0);
setvbuf(g, NULL, _IONBF, 0);
fread(&x[1], 1, 2, f);
fwrite(&y[1], 1, 2, g);
printf("x = %s\n", x);
printf("y = %s\n", y);
fclose(f);
fclose(g);
printf("x = %s\n", x);
printf("y = %s\n", y);
return 0;
}
</pre>
Desired Action:
Clarify whether the implementation must behave as if it was using memmove
internally, or alternatively, that it is up to the application to avoid
fread/fwrite calls on memory streams that will trigger such copies. The
latter seems hard to do in general.
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Issue History
Date Modified Username Field Change
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2017-06-22 08:02 Villemoes New Issue
2017-06-22 08:02 Villemoes Status New => Under Review
2017-06-22 08:02 Villemoes Assigned To => ajosey
2017-06-22 08:02 Villemoes Name => Rasmus Villemoes
2017-06-22 08:02 Villemoes Section => fmemopen
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