Bug 35925 - -g1 causes "Error: file number 1 already allocated"
Summary: -g1 causes "Error: file number 1 already allocated"
Alias: None
Product: gcc
Classification: Unclassified
Component: debug (show other bugs)
Version: 4.2.3
: P3 normal
Target Milestone: ---
Assignee: Not yet assigned to anyone
Depends on:
Reported: 2008-04-13 17:29 UTC by Mark Seaborn
Modified: 2008-04-29 21:02 UTC (History)
1 user (show)

See Also:
Known to work:
Known to fail:
Last reconfirmed:


Note You need to log in before you can comment on or make changes to this bug.
Description Mark Seaborn 2008-04-13 17:29:19 UTC
$ echo "void foo(void) { }" >test.c
$ gcc -g1 -S test.c
$ gcc -g1 -c test.s
test.s: Assembler messages:
test.s:79: Error: file number 1 already allocated

If "-g1" is changed to "-g", "-g0" or "-g2", or is removed, the error goes away.

This causes problems when building glibc with CFLAGS="-g1".  glibc's configure script invokes gcc as above in order to test whether --noexecstack is available.  It gets an error and wrongly concludes that --noexecstack is not available, which means libc.so doesn't get the benefit of a non-executable stack.

Is this supposed to work, or should glibc work around it, perhaps by not passing CFLAGS to the second invocation of gcc?
Comment 1 Jim Wilson 2008-04-14 23:56:10 UTC
There is a conflict between the gcc and gas debug info support here.  This can't be fixed in gcc.  It will have to be fixed in binutils.

-g1 tells gcc to emit debug info, but not line number info.  We do emit file and line number info for function definitions.  This involves emitting a .file 1 "tmp.c" directive to add an entry to the dwarf2 file table.

-g tells gas to try to emit debug info.  Gas sees that there is no line number info, and so tries to generate some itself.  However, gas is allocating entries from the same dwarf2 file table that gcc is allocating from, leading to conflicts.  Since gcc runs first, gcc can't avoid the conflicts.

I can make this work for a trivial example if I change gcc to emit the .file directive for function info earlier.  However, this doesn't solve the problem, it just delays it.  If I change the testcase so that it includes another source file, then it fails again, this time complaining that file number 2 is already used.  This one is impossible to fix in gcc.

Binutils needs to be changed to either not emit line number debug info for a file compiled with gcc -g1, or else to allocate virtual file numbers for its debug info, and then only give them physical file numbers when it is finished parsing the entire file, and hence knows how many file numbers that gcc used.

I suggest filing a bug with the binutils folks pointing back at this bug report.
Comment 2 Mark Seaborn 2008-04-29 21:02:32 UTC
Thanks for the explanation.  I have filed a bug on glibc with a simple workaround (http://sources.redhat.com/bugzilla/show_bug.cgi?id=6428).  Changing binutils is not necessary to fix glibc's configure check.