[BZ #5012]

Update.
2008-02-22  Andreas Jaeger  <aj@suse.de>,
	    Carlos O'Donell <carlos@systemhalted.org>

	[BZ #5012]
	* FAQ.in: Describe why glibc needs to be compiled with
	optimization.

1 files changed, 36 insertions, 6 deletions

diff --git a/FAQ b/FAQ
index 77bd47e3ed..9b557dae17 100644
--- a/FAQ
+++ b/FAQ
@@ -50,6 +50,9 @@ please let me know.
 1.21.	Which compiler should I use for powerpc64?
 1.22.	`make' fails when running rpcgen the first time,
 	what is going on? How do I fix this?
+1.23.	Why do I get:
+	`#error "glibc cannot be compiled without optimization"',
+	when trying to compile GNU libc with GNU CC?
 
 2. Installation and configuration issues
 
@@ -484,12 +487,12 @@ down the build process and need more disk space.
 failure should be looked into.  Depending on the failures, you probably
 should not install the library at all.
 
-You should consider using the `glibcbug' script to report the failure,
-providing as much detail as possible.  If you run a test directly, please
-remember to set up the environment correctly.  You want to test the compiled
-library - and not your installed one.  The best way is to copy the exact
-command line which failed and run the test from the subdirectory for this
-test in the sources.
+You should consider reporting it in bugzilla
+<http://sourceware.org/bugzilla/> providing as much detail as possible.
+If you run a test directly, please remember to set up the environment
+correctly. You want to test the compiled library - and not your installed
+one. The best way is to copy the exact command line which failed and run
+the test from the subdirectory for this test in the sources.
 
 There are some failures which are not directly related to the GNU libc:
 - Some compilers produce buggy code.  No compiler gets single precision
@@ -589,6 +592,32 @@ yourself. Please remember that for each architecture there may be various
 patches required to get glibc HEAD into a runnable state. The best course
 of action is to determine if you have all the required patches.
 
+
+1.23.	Why do I get:
+	`#error "glibc cannot be compiled without optimization"',
+	when trying to compile GNU libc with GNU CC?
+
+{AJ,CO} There are a couple of reasons why the GNU C library will not work
+correctly if it is not complied with optimzation.
+
+In the early startup of the dynamic loader (_dl_start), before
+relocation of the PLT, you cannot make function calls. You must inline
+the functions you will use during early startup, or call compiler
+builtins (__builtin_*).
+
+Without optimizations enabled GNU CC will not inline functions. The
+early startup of the dynamic loader will make function calls via an
+unrelocated PLT and crash. 
+
+Without auditing the dynamic linker code it would be difficult to remove
+this requirement. 
+
+Another reason is that nested functions must be inlined in many cases to
+avoid executable stacks.
+
+In practice there is no reason to compile without optimizations, therefore
+we require that GNU libc be compiled with optimizations enabled.
+
 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
 
@@ -1957,6 +1986,7 @@ Answers were given by:
 {AO} Alexandre Oliva, <aoliva@redhat.com>
 {BH} Bruno Haible, <haible@clisp.cons.org>
 {SM} Steven Munroe, <sjmunroe@us.ibm.com>
+{CO} Carlos O'Donell, <carlos@systemhalted.org>
 
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