Re: [uml-devel] Segfault on UML load

["Charles A. Clinton" <cac@cac.seattle.wa.us>]

On Wed, 31 Mar 2004, I wrote:

> When I build a UML kernel on my Fedora Core 1 machine, it segfaults when 
> it tries to load.

Blaisorblade pointed me to a 2.6 patch set which provides the answer.
The link.ld script puts an empty 4K page at the front of the UML image.
The Fedora glibc expects the elf program headers to be at the start of the
image and searched them form information regarding stack executability. 
The empty page is not mapped, and the search segfaults. I suspect that 
there is a bug in binfmt_elf that is not taking into account the load 
offset when setting up the aux vector, but the code is so convoluted there 
that I am mostly dazed.

Anyway, the following patch (adapted from
http://toast.debian.net/~may/umlproject/unpackaged/align.patch) when 
applied on top of uml-patch-2.4.22-1, fixes the problem. It should work
for any of the 2.4.x patches.

Thanks to Blaisorblade for pointing me to the UML for Fedora page.

diff -Naur linux-2.4.22/arch/um/dyn_link.ld.in linux-2.4.22.works/arch/um/dyn_link.ld.in
--- linux-2.4.22/arch/um/dyn_link.ld.in	2004-04-01 11:26:04.000000000 -0800
+++ linux-2.4.22.works/arch/um/dyn_link.ld.in	2004-04-01 11:32:35.000000000 -0800
@@ -8,7 +8,6 @@
 {
   . = START() + SIZEOF_HEADERS;
   .interp         : { *(.interp) }
-  . = ALIGN(4096);
   __binary_start = .;
   . = ALIGN(4096);		/* Init code and data */
   _stext = .;
diff -Naur linux-2.4.22/arch/um/link.ld.in linux-2.4.22.works/arch/um/link.ld.in
--- linux-2.4.22/arch/um/link.ld.in	2004-04-01 11:26:07.000000000 -0800
+++ linux-2.4.22.works/arch/um/link.ld.in	2004-04-01 11:32:19.000000000 -0800
@@ -6,7 +6,6 @@
 {
   . = START() + SIZEOF_HEADERS;
 
-  . = ALIGN(4096);
   __binary_start = .;
 ifdef(`MODE_TT', `
   .thread_private : {


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